transformer Related Articles

Ⅰ IntroductionIf you've been around electrical equipment for a long time, you may have heard of the transformer. Yeah, they're the enormous bulky things found in the corners of the street that make random scary noises and spit sparks sometimes. There is also a sort of small transformer in your phone charger, but much, much smaller and with a different mechanism.CatalogⅠ IntroductionⅡ Transformer DefinitionⅢ Importance of Transformers in Electrical SystemⅣ Transformer SymbolsⅤ Working Principle of a TransformerⅥ Transformer PropertiesⅦ Transformer Construction  7.1 BOBBIN  7.2 CORE  7.3 WINDINGSⅧ Transformers ApplicationⅨ ConclusionⅩ FAQⅡ Transformer DefinitionA transformer is a device that converts one voltage or current to another using the principles of electromagnetism. It consists of a pair of wounds around a magnetic core of the insulated wire. The winding to which the voltage or current to be converted is connected is called the primary winding and the secondary winding is called the output winding. Transformers come in two types: step up, which increases the voltage or current, and step down, which lowers the input of the voltage or current. The transformers in your microwave oven, for example, are a secondary transformer that is used in the microwave oven to supply about 2200Volts to the vacuum tube. One thing to remember is that transformers only operate with AC voltages or adjustments and do not work with DC. We'll understand why now. Ⅲ Importance of Transformers in Electrical SystemIt was around 1856 that there was a rivalry between two brilliant minds, Nikola Tesla and Thomas Edison. Those were the days when electricity and its applications were merely noticed by glowing a lamp and driving a motor. It was Edison and his associates who first discovered the DC (Direct Current) system, and then Tesla developed his AC (Alternating Current) system sometime after that. The two have since tried to show that their scheme is more advantageous than the other. The time has come for houses to get electricity by then. Although Edison was busy showing how dangerous AC is by electrocuting elephants, Tesla and his team came up with the transformers that made it much simpler and more effective to transmit electricity. Also, transformers play a key role in the transmission system today. Let's learn why. High-voltage and low-current transmission of electricity will help us minimize the thickness of the transmission wires and thus the cost, which will also improve the system's performance. For this purpose, a typical transmission system may be anywhere from 22KV to 66KV, although some generators have an output voltage of only 11kV in the power plant and need only 220V/110V for the household AC unit. So where does this transfer of voltage take place and who does it? Transformers are the answer to the issue. There will be transformers in the system from the power plant to your home that will either step-up the voltage (increase voltage) or step-down (decrease voltage) to preserve the system's efficiency. The transformers are therefore referred to as the heart of an electrical transmission system. In this post, we will be learning more about them. Ⅳ Transformer SymbolsFor a transformer, the circuit symbol is simply two inductors placed together side by side that share the same center. The type of core used is shown by the existence of the line between the two windings: a dashed line represents ferrite, two parallel lines represent laminated iron, and no line represents the core of air.The number of 'bumps' is often used as a rough measure of the role of the transformer-less bumps on one side and more on the other which means that there is a lower number of turns on the first side than the other.Ⅴ Working Principle of a TransformerWe need to go back in time, to the laboratory of Michael Faraday, to understand the operation of a transformer. Perhaps the father of the transformer can be named Michael Faraday, as it was his experiments that helped us understand electromagnetism and create devices such as motors and generators. There was a race to try to create a practical system that could harness the strength of magnets to produce electricity in the late 1800s when it was discovered that electricity and magnetism were related phenomena. Faraday figured out that by bringing a magnet close to a coil of wire, electricity could be produced. What he discovered was that only when the magnetic field shifts can the voltage be produced, that is, whether either the coil or the magnet is shifted relative to the other. In DC, the movement of the current is constant and so is the magnetic field. There is no voltage generated on the secondary because the field is constant and not changing and the transformer just looks like a regular coil of resistive wire to the power supply. So, with DC currents, transformers do not operate. He also found that a current flowing in one coil might cause the current in the other coil when two coils of wire were held close to each other. This definition is referred to as mutual inductance, which governs the operation of all modern transformers.The transformer consists of two windings wound on a magnetic core, as shown in the figure. The goal of having a core is that air is not a very good magnetic field supporter, so having a magnetic core increases the magnetic field for a certain amount of current flowing through one winding, which in turn generates a stronger current in the other, improving the device's overall performance. A magnetic field is built up in the core as a current moves through the primary and is limited mostly to the core. This magnetic field passes through the center of the secondary and, thus, the law of reciprocal induction causes a current in the other. The beauty of this method is that the ratio between the input voltage and the output voltage is simply the ratio between the main and the secondary windings, summarized by the following formula:Vout/Vin = Nsec/NpriVin is the input voltage, Nsec is the number of turns in the secondary winding, and Npri is the number of turns in the main winding, where Vout is the output voltage.So if you have two transformers, one with 100 turns on the primary and 1000 turns on the secondary and one with 10 turns on the primary and 100 turns on the secondary, you can measure the ratio of turns to be 1:10 on both of them, so that they both increase voltage to the same degree. Ⅵ Transformer PropertiesIf we take a closer look at the above example, the first transformer would have higher winding resistance (since more wire is used) and will restrict the amount of current that can be drawn from the transformer in certain instances. This property is called winding resistance, but since the copper wire used normally has a low resistance, it does not matter in most cases. Another thing you see is that the main and secondary windings have no direct electrical connection. This is called galvanic isolation and, as we can see, can be very useful. Looking at each of the transformer windings, we can see that they are shaped like inductors and also have an inductance, a coil of wire wrapped around a magnetic center. This inductance, given by this formula, is proportional to the square of the number of turns:Lpri/Lsec = Npri2/Nsec2Where Lpri is the primary winding inductance, Lsec is the secondary winding inductance, Npri is the number of turns on the primary windings and Nsec is the number of turns on the secondary windings. The proportionality constant can be found in the datasheet for a given core and is typically given in μH/turn2 units. The exact value is based on the core form and scale. Suppose you have a transformer core with a 1uH/turn2 specification. If you wind one winding on that heart, the value of the constant multiplied by the number of turns squared will be the inductance, in this case, 1. So the winding inductance of that one will be 1μH. If you wind the same core with another winding with 10 turns, then the inductance will be:(1µH/turn2)*(10 turns)2 = 100µHSince the windings have inductance, they provide an impedance to AC signals, given by the formula:XL = 2π*f*LWhere XL is the impedance in ohms, f is the frequency in ohms and L is the inductance in Henries.Say, you want to design a transformer at 50Hz, which is the standard power line frequency, that draws 3A at 220V AC. Then, by Ohm's law, the impedance of the main will need to be 73.3 Ohms. Now that we know the appropriate impedance and the frequency, we can rearrange the formula to find out the inductance required for the winding:L = (XL)/(2π*f)Substituting the values, we find that 233mH would be the required inductance.We can calculate the windings necessary to get the inductance needed using this information and the value of μH/turns2 from the datasheet.Assuming the value is 50μH/turns2, we can rearrange the formula to evaluate the inductance: Where N is the number of turns, L is the inductance required, and the term t2/μH is just the inverse of the value of the datasheet.We get the necessary number of turns of 2158 when adding our values to the formula. So, as you can see, you can build transformers for almost any application once you get the hang of the formulas! Ⅶ Transformer ConstructionAn awareness of transformer construction is vital for someone who wants to wind their own transformers.A transformer is made up of a few fundamental components: 7.1 BOBBINFor every transformer, the bobbin is the fundamental structure. It provides a spool on which the windings will wind and keeps the core in place as well. It is typically composed of plastic that is heat resistant. It also sometimes involves metal pins onto which, for example, you can weld the ends of the windings if you want to mount it to a PCB. 7.2 COREPerhaps the most significant aspect of the transformer is this. The cores can come in several shapes and sizes, as seen in the image. It is the core's magnetic properties that decide the transformer's electrical properties that are built around the core. 7.3 WINDINGSThe wire used in the house, though it can seem like a trivial item, is as critical as any other element. In general, solid enameled copper wire is used because the insulation is strong and thin, so plastic insulating sheaths do not waste space. Ⅷ Transformers Application • MAINS VOLTAGE CONVERSIONThis is possibly the most common transformer application, stepping down the mains voltage for low voltage devices. This stuff, like microwaves and old TVs and wall brick power supplies, you might even find inside. These transformers have iron cores that make them bulky and much less efficient than other types, providing excellent permeability.Three secondary wires mark them as 12-0-12 or 6-0-6. If you make the center wire the ground reference, this means that the outer two wires have an output of 12V AC RMS. If you calculate the 12v winding over each, you get 24V AC RMS. This gives you the flexibility to use the transformer as you may like. • SWITCH MODE POWER SUPPLIESThese are very specific type of power supplies that generate a DC output and take a DC input. Both modern phone chargers are located here. The transformers used in these PSUs are shaped more like medium- to high-permeability inductors with a limited number of turns and ferrite cores. For a brief period, a DC voltage is applied across the 'primary' so that the current ramps up to a certain amount and retains some magnetic energy in the core. At a lower voltage, this energy is then passed to the secondary, since it has a smaller number of turns. They work and achieve outstanding efficiencies at high frequencies and are very thin. • ELECTRICAL ISOLATIONThere are special transformers with a 1:1 turn ratio, such that the voltages of the input and output are the same. They are used to decouple equipment from the earth's mains. Since mains are referred to as earth, touching even one wire will lead to a shock since the return path is simply the ground. The unit is separated from the main earth by the use of isolation transformers, as transformers are galvanically insulated. • VOLTAGE CONVERSION TRANSFORMERSMany countries use 220V AC as the normal supply voltage around the world, but some countries use 110V AC, such as the US. This means that it is not possible to operate certain devices such as blenders in all countries. To this end, transformers that convert from 110V to 220V or vice versa can be used to ensure that appliances can be used in any region. • IMPEDANCE MATCHINGThere are unique transformer types that are used to balance the source and load impedance. RF and audio circuits are commonly used.The ratio of turns is equal to the source's square root and load impedance. • AUTOTRANSFORMERThis is a special type of transformer that has only one winding that forms the secondary with a 'tap' output. This tap is normally variable, so the output AC voltage can be varied, much like a voltage divider. Ⅸ ConclusionTransformers are useful instruments and it can be very useful to learn how to build and operate with them! Although we have covered the basics here, it is something that can be discussed in another whole article to build a transformer right from scratch, so for some other time. But now, you'll know why it's there and how it works when you see a transformer again. Ⅹ FAQ1. How does a transformer convert AC into DC?The transformer is not designed to convert ac to dc. It is a pure AC device used to step down/up voltage levels keeping frequency, power, FLUX constant. In mobile charger, we use transformer along with bridge rectifier to convert domestic AC supply to dc. (with ripples) Finally, such a transformer that converts ac to dc is not designed yet. 2. Will a transformer work with DC?Transformers work in the principle of Faraday's law of 'mutual induction', in which an EMF is induced in the transformer's secondary coil by the magnetic flux generated by the voltages and currents flowing in the primary coil winding. As in DC(voltage being always constant), the change in flux is zero so no mutual induction, thus transformers can't work with a DC supply. Moreover, if DC or a similar rating of AC(Voltage & Current) is fed into the terminals of a Transformer there is a high possibility that it would burn the primary coil. 3. What is a transformer's simple definition?Transformer, device that transfers electric energy from one alternating-current circuit to one or more other circuits, either increasing (stepping up) or reducing (stepping down) the voltage. 4. What is the use of a transformer?Transformers are most commonly used for increasing low AC voltages at high current (a step-up transformer) or decreasing high AC voltages at low current (a step-down transformer) in electric power applications, and for coupling the stages of signal-processing circuits. 5. What is the basic principle of a transformer?A transformer consists of two electrically isolated coils and operates on Faraday's principle of ‘mutual induction’, in which an EMF is induced in the transformer's secondary coil by the magnetic flux generated by the voltages and currents flowing in the primary coil winding. 6. What are the two types of transformer?The different types of transformer are Step up and Step down Transformer, Power Transformer, Distribution Transformer, Instrument transformer comprising current and Potential Transformer, Single phase and Three phase transformer, Auto transformer, etc. 7. What are the main parts of the transformer?There are three basic parts of a transformer:• an iron core that serves as a magnetic conductor,• a primary winding or coil of wire.• a secondary winding or coil of wire. 8. What does a transformer look like?A transformer keeps wired doorbells powered at the right voltage for optimal operation. It looks like a small metal box and can be silver, off-white, or even brass colored. If your doorbell is no longer working, you may need to troubleshoot the transformer in order to perform the repair. 9. What is a transformer ratio?The transformer turns ratio is the number of turns of the primary winding divided by the number of turns of the secondary coil. The transformer turns ratio provides the expected operation of the transformer and the corresponding voltage required on the secondary winding. 10. What are the ideal transformers?A transformer that doesn't have any losses like copper and core is known as an ideal transformer. In this transformer, the output power is equivalent to the input power. The efficiency of this transformer is 100%, which means there is no loss of power within the transformer. 

CatalogⅠ Isolation Transformer DefinitionⅡ Isolation Transformer ConstructionⅢ How Isolation Transformers Work?Ⅳ What's the Main Function of an Isolation Transformer?Ⅴ Special Purpose Isolation Transformers 5.1 Pulse Transformers 5.2 Austin Transformers 5.3 Instrument TransformersⅥ What are the Benefits of Isolation Transformers?Ⅶ Isolation Transformers VS AutotransformersⅧ FAQⅠ Isolation Transformer DefinitionTwo copper coils that are wrapped around each other and are each supplied by their own power source make up an isolation transformer. While the term "isolation transformer" applies technically to any transformer, it is specifically a transformer that isolates an alternating current from a circuit. By separating two circuits with an induction loop or lowering the voltage of the alternating current until it enters the circuit itself, an isolation transformer does this. Transformers isolated from each other with main (input) and secondary (output) windings are known as isolation transformers. Under this configuration, a dielectric insulation barrier electrically separates the input power and output power.Ⅱ Isolation Transformer ConstructionTransformers can be described as two coils surrounding a core of ferromagnetic material, as shown in Figure 4.The main and secondary coils are shown in the schematic representation; the electric source is connected to the primary, and the isolated output is taken from the secondary. Physically, the coils are distinct from each other and the heart. An early transformer was first used by Michael Faraday during his studies studying electromagnetism. Faraday found that a current-carrying wire generates a magnetic field surrounding the wire and that a current in one generated a magnetic field when two different wires were coiled around a toroid of soft iron, and the changing flux, in turn, induced a voltage in the other. Now known as mutual induction, Faraday is credited with finding that a shifting magnetic flux is caused in a circuit by an electromotive force according to the formula:Sometimes this is shown using the absolute value of E:  The negative indicating the electromotive force opposes the current.Although isolation is provided by any transformer consisting of two separate coils and no grounding shields, the term isolation transformer applies to transformers specifically designed for electrical insulation, the primary purpose of which is to isolate the AC source from circuits, devices and primary and secondary windings. They also have special insulation between the primary and secondary coils and are built between windings to withstand high voltages. Since the capacitance and resistive paths of the coils can be connected to power line/transient voltage noise, isolation transformers have additional features to minimize common-mode noise (which occurs on both hot and neutral ground-referenced wires), transverse mode noise (which occurs between hot and neutral wires) and electromagnetic noise. DC signals and interference caused by ground loops are blocked by the transformer. To reduce any capacitance between the windings, electrostatic shields are used for sensitive equipment (computers or measuring instruments). The insulation transformers used for protection generally have a 1:1 turn ratio, with the number equal to the turns in the primary and secondary windings, but when the voltage still needs to be changed, step-up and step-down isolation transformers are used. Check the specifications for the included features, the scores, and how they are designed when selecting an isolation transformer.Ⅲ How Isolation Transformers Work?Isolation transformers act in the same manner as other transformer types. To allow the primary coil to induce a current in the secondary coil, the isolation transformer is made of two electromagnets that are wrapped around each other. If more than the secondary coil is wound in the primary coil, the voltage is diminished. If more than the primary coil is wound into the secondary coil, the voltage is increased. In order to maintain the same voltage but to distinguish two circuits, an isolation transformer could have primary and secondary coils that are wound the same by causing a current from one coil to the other rather than providing a direct link.Ⅳ What's the Main Function of an Isolation Transformer?Its main role is to include certain circuits that are not capable of directly handling an alternating current safely. Not only does this ensure the full protection of your system, but it also helps to prevent short-circuits or fire accidents. It is included in most of the equipment to reduce the voltage until it hits the application for safety purposes. Another essential feature of using this transformer is that it helps to manage any required amount of voltage.Ⅴ Special Purpose Isolation TransformersIsolation transformers have been developed for specialized applications. Some examples are:5.1 Pulse Transformers: Optimized for the propagation of rectangular electrical pulses and to provide digital signal electrical isolation. These are used in the networking of computers.5.2 Austin Transformers: These power the air-traffic obstacle lamps you see on antenna structures, invented by Arthur O. Austin. The lighting circuitry on the antenna mast would conduct radio-frequency energy to the earth, if not isolated. The AC building mains are also completely separated from the tower by these transformers.5.3 Instrument Transformers: They are used to provide reliable voltage for meters and to securely isolate control circuits from high voltages/current. The transformer's primary winding is linked to the high voltage/current circuit and the meter, much like the connections shown in Figure 3, is linked to the secondary circuit.Note: Some transformers are manufactured with only one winding that is tapped on the winding at various locations to split it into main and secondary portions. Known as auto-transformers, as the single winding is shared, these devices do not provide isolation. Separate coils have isolation transformers, with no physical connection between the coils, no ground on earth.Ⅵ What are the Benefits of Isolation Transformers?Because of their diverse uses and advantages, different industries and companies use isolation transformers. Some of its most significant advantages are listed here.• Isolation can be replaced by isolation transformers in various circuits. With a 1:1 ratio, the main and secondary windings can be separated by insulation transformers.• Transformers of isolation allow direct current power isolation simpler. In the case of telephone lines, where amplifiers are needed at different intervals, the separation of direct current components from the signal is performed by isolation transformers to control every amplifier on the line.• By uniting a vessel with the electric power source, isolation transformers eliminate the possibility of electric shock. They allow the isolation of the person from the resource in such a way that the electrical wires do not directly contact the power line.• Without isolation in electronics testing and servicing, it can prove dangerous to contact a live portion of the circuit. For isolation, 1:1 ratio transformers are therefore used to provide protection. For gadgets that use electricity, isolation transformers have therefore proven to be an excellent choice.• With the aid of isolation transformers, all kinds of noise and sound produced by connecting the signal from the audio amplifier to the speaker output circuit are minimized.• The amount created by a radio frequency on wide circuit devices is separated from the transmitter line by isolation transformers. They facilitate the relation to the transmitted signals of the amount generated by the radio frequency amplifier and direct it toward the antenna.Ⅶ Isolation Transformer VS AutotransformerAn isolation transformer is a main and secondary coil winding electrical transformer. By insulation, these windings are isolated. This insulation reduces the possibility of electrocution by simultaneously contacting the active components and the ground.An autotransformer is a single-winding electrical transformer. The term "auto" applies not to any kind of automatic system but single-coil working alone. Portions of the same winding serve as both the main and secondary sides of the transformer in an autotransformer.• Operation of an Isolation TransformerAn isolation transformer's primary function is to separate circuits. These transformers are designed and produced between the two windings with attention to capacitive coupling. Alternating current (AC) current from the primary to the secondary will also be coupled by the capacitance between primary and secondary windings.• Operation of an AutotransformerAn autotransformer's primary function is to control the transmission line voltage and can be used to convert voltages. An autotransformer automatically changes the voltage according to the load, with only one winding. Such transformers require the correct operation of AC currents and will not operate on direct current.• Common Applications for an AutotransformerBoost at end of the long transmission line to compensate for line lossesReduced starter voltage for an induction motorTo enable rectifier output control, multi-tap feeding the primaryFluorescent light fixture start-up• Common Applications for an Isolation TransformerComputers and peripheralsMedical EquipmentRemote control equipmentTelecommunication equipment Ⅷ FAQ1. What is an isolation transformer?Isolation transformer is basically a transformer with winding ratio of 1:1, i.e., it has same number of primary as well as secondary windings.Isolation transformer provides electrical isolation between two circuits by transfering energy in magnetic form from one circuit to another.First circuit is connected in primary of transformer. Electric supply on this circuit is converted to magnetic field on primary winding and magnetic field magnetises secondary winding which is converted into electrical energy again in secondary circuit. Since it has 1:1 winding ratio voltage and current level of secondary circuit are same as that of primary circuit. So both circuits are electrically isolated yet energy is being transferred between them. 2. Where and why are isolation transformers used?As the name suggests, they are used to isolate the two circuits electrically by providing a galvanic isolation between them. There are many reasons to use an isolation transformer.Isolation transformers block transmission of the DC component in signals from one circuit to the other, but allow AC components in signals to pass.Isolation transformers are used for impedance matching to get the most efficient power transfer between stages and to keep different stages electrically isolated to prevent ground loops.Isolation transformers prevents harmonics from transferring from one side to other side. 3. How does an isolation transformer protect against an electric shock?It doesn’t always protect against an electric shock but it will protect against an electric shock to earth for a single fault in a Multiply Earthed Neutral (MEN) system. Current needs a return path to the source and if teh secondary windings of the isolating transformer are not earthed then there is no return path for current flowing through the person back to the other terminal of the secondary winding. All that happens is that the contacted winding assumes the earth potential.You will still get shocked if you contact both terminals or if you have multiple devices with earth faults that provide a return path for the current.The benefit is that the isolating transformer continues to supply current even in the event of a short to earth on one of its secondary windings. 4. What are the disadvantages of isolation transformer?The Isolation Transformer is a specially designed transformer which is used to isolate two different electrical circuits. The Isolation Transformer is mainly used to isolate the load or powered device from the power supply.Some Disadvantages of Isolation Transformer are given below.• When the Isolation Transformer operating as Pulse Transformer and it operate at low frequency there is distortion produces in secondary or output waveform.• When isolation transformer operating at DC pulse signal, the saturation property of the core reduces.• Isolation Transformer specially designed, that is why it is costlier than a normal transformer. 5. What's the difference between an isolation transformer and a regular transformer?• The transformers having primary and secondary winding which are separated from each other known as Isolation transformer where as Regular Transformer are used for sending and receiving electricity .• Isolation transformers are not used to increase or decrease voltage and Regular Transformer is used to increase or decrease the voltage and current in an electrical circuit.• There are used to breaking the circuit into primary and secondary, so direct current noise can’t get through. Regular Transformers are designed to modify an alternating current voltage that runs from one electric circuit to another through electromagnetic induction. 6. What is the difference between isolation transformer and step up transformer?Main purpose of isolation transformer is to electrically isolate two sides or circuits. This is done mostly for safety reasons. You may make the second side shock proof, or it may have its own DC supply.Usually the turns ratio of isolation transformer is one, meaning input and output will be same in magnitude, though occasionally it could be different.While primary of transformer may be connected to live wire, secondary becomes safe from electric shock. Two different circuits can be connected this way.Step up transformer is used for increasing the voltage from one level to a higher one. Main purpose is to have higher voltage level for the circuit on secondary side. The two sides may or may not be isolated, and turns ratio is greater than one. 7. What is the working principle of an isolating transformer?Isolation transformer is just similar to our normal transformer but the difference is in the transformation ratio. It is 1:1 in isolation transformer. So it also works on the Faraday's law of mutual induction. It says that the emf induced in the secondary coil due to te production of magnetic flux by the voltages and currents of the primary coil. 8. What are the applications of isolating transformers?• The main application of Isolation Transformer is, to make the isolation between a power supply and a powered circuit or powered device for the safety purpose.• Isolation Transformer is used to transform electrical power between two circuits which are not connected electrically to each other. Those two circuits are may have the same voltage level or different voltage level.• Isolation transformers are can be used as Pulse Transformer.• Isolation transformers are used for computer network design. Here isolation transformer act as Pulse Transformer.• Sometimes the Isolation Transformer used in electrical circuits as well as an electronic circuit to provide protection against Electrical shock. 9. Why do we need an isolation transformer to connect an oscilloscope?The scope input shield is connected to the power outlet ground via the scope chassis for safety. It should never be connected to any point not at the same potential as that ground.Either the device under test should also be grounded, or completely isolated from ground. The isolation transformer is the preferred method in most cases.When testing circuits solely using DC power, a lab type DC supply may have outputs isolated from ground. This is also acceptable.It is important to think of all possible paths that arise through connections to other equipment, or parts of a system. The isolation transformer is safe in the most situations.  10. What is the working process of an isolation transformer?Isolation transformers are very important for providing isolation in medical instruments powered by the mains grid (220 V or 110 V AC), which is connected to the primary of an isolation transformer, but where the electronic network connected to the patient is connected to the secondary of the transformer. Since the secondary network is isolated from the primary, there is no path for an AC current from the mains to go to the ground through the patient. 

I IntroductionThis article introduces the basics of low voltage transformer, including the definition of low voltage transformer, the principle of low voltage transformer, its installation method, malfunction, and how to repair a household low voltage transformer. A transformer is an electronic instrument that we can use everywhere in our lives. For example, we are inseparable from the mobile phone chargers. The internal components also have transformers. For example, the power supply in our computers is also composed of transformers. Therefore, all electronic products are indispensable for transformers. The transformers used in electronic components are all power transformers (included low voltage transformers). The power transformer is mainly used in electronic products to convert the power supply to the voltage required by the electronic circuit.CatalogⅠIntroductionⅡ Basics of low voltage transformer2.1 Definition of low voltage transformer2.2 Types of low voltage transformers2.3 How does low voltage transformer work?2.4 Design requirements of low voltage transformer2.5 Application environmentⅢ Differences between low&high voltage transformerⅣ How to Estimate the Loss of Low Voltage TransformerV Guide to What You May be Interested in5.1 How to Install Low Voltage Transformer for Household?5.2 How to Troubleshoot a Low-Voltage Transformer5.3 Repairing a household transformer5.4 Malfunction of factory low voltage transformerVI One Question Related to Low Voltage Transformer6.1 Question (Multiple choice questions)6.2 AnswerVII FAQII Basics of Low Voltage Transformer2.1 Definition of Low Voltage Transformer Transformers are important power equipment in our life, especially low-voltage transformer. Whether it is for large-scale power plants or home circuits, it is inseparable from the transformer. There are two kinds of transformers used in our life, one is the high-voltage transformer which used in the high-voltage or ultra-high-voltage circuit, the other is the low-voltage transformer which used in the family lighting circuit or small power circuit.The so-called low-voltage transformer refers to the transformer with low load voltage. As long as the load is lower than 600V, it can be called a low-voltage transformer. The low-voltage transformer is mainly composed of primary coil, secondary coil, and a magnet iron circuit. Low voltage transformers are commonly used for low voltage lighting, which typically only uses 12 or 24 volts. 2.2 Types of Low Voltage TransformersThere are two main types of low voltage transformers: electronic and magnetic.（1）Electronic Low Voltage TransformersElectronic transformers are much smaller, lighter, and less expensive than magnetic counterparts. But they only have about a 5-6 year lifespan. Also, electronic low voltage transformers are known for being noisy.Electronic Low Voltage TransformersAdvantagesDisadvantages▪ Smaller and lighter, easier to hide▪ Less expensive▪ Shorter life span▪ Noisy▪ Heat-sensitive（2）Magnetic Low Voltage TransformersThere are two types of magnetic transformers: stack laminated and toroidal.  Stack laminated transformers have a longer lifespan, about 15 to 20 years. But they only operate at about 80 to 85 percent efficiency, also are known for being noisy.Toroidal transformers are very quiet and more energy efficient. They can operate at about 90 to 95 percent efficiency. And they are long-lived, lasting 20 to 25 years.Magnetic Low Voltage TransformersAdvantagesDisadvantages▪ Long life span of over 15 years▪ Energy efficient▪ Quiet▪ Heavy, big, and difficult to hide▪ Expensive2.3 How Does Low Voltage Transformer Work?Electricity and magnetism are two kinds of energy that can mutually transform. Electricity can generate magnetism, and magnetism can also generate electricity. The low-voltage transformer uses this principle to adjust the voltage through the mutual conversion of electricity and magnetism.A low voltage transformer consists of two electrical coils of wire, one of which is called primary winding and the other is called secondary winding. The primary side of the transformer collects power and the secondary side provides power.Figure 1. Low Voltage Transformer StructureThe two coils intertwine together on a magnet iron circuit core, but without electrically in contact with each other. The magnetic core is made of soft magnetic material, which consists of laminations connected together to help reduce core loss. The core allows power to be transferred from one coil to another. When the primary winding is connected to the power supply, the generated magnetic field transfers the voltage to the secondary winding.Figure 2.  How Does Low Voltage Transformer Work?In summary, the primary winding transforms the electrical power into magnet field when connected to the input voltage supply while secondary winding transforms alternating magnetic field into electrical power of required output.2.4 Design Requirements of Low Voltage TransformerThe low-voltage transformer should be vacuum cast, molded resin encapsulated, 60Hz, Class F insulation, comply with the requirements of IEC726, and meet the requirements of capacity, voltage, phase number, and wiring shown. Each low-voltage transformer has separate primary and secondary windings, and there are two 2.5% normal voltage full-capacity taps above and below the rated voltage on the primary side. The low-voltage transformer should be installed on a base that can isolate, reduce vibration and noise, and the iron core and coil should be properly fixed to withstand the mechanical stress generated in the event of line failure and can withstand 16460 Lite 16460-6 V2. 0 2002/ 11/ 25 Vibration and impact during shipment. Unless otherwise specified, the impedance of low-voltage transformers shall be in accordance with IEC 726. The average noise level of the low-voltage transformer should not exceed the value specified in IEC 726. Each dry-type low-voltage transformer should have appropriate terminals to accommodate the required primary and secondary wiring connections. Low-voltage transformers can be reserved for cable entry from either side or bottom.2.5 Application Environment(1) Ambient air temperature - 5 ℃ to + 40 ℃, 24-houraverage value not more than + 35 ℃(2) The altitude of the installation site shall not exceed 2000m(3) The relative humidity of the atmosphere shall not exceed50% when the ambient air temperature is + 40 ℃(4) A place without violent shaking and impact vibrationIII Differences Between Low&High Voltage Transformer Low Voltage TransformerHigh Voltage Transformerwindingcontinuous windingInterleaved WindingscoolingOil-immersed cooling or air coolingOil-immersed coolingstructureoil tank structurebell jar type oil tankⅣ How to Estimate the Loss of Low Voltage TransformerTransformer loss include copper loss and iron loss. The loss of iron loss is also called no-load loss, and the loss of copper loss is also called load loss. The open circuit of the secondary winding of the transformer applies the no-load current of rated frequency and rated voltage to the primary side, and the active loss caused by the transformer core is called the no-load loss of the transformer. The loss figure can be obtained by the unit loss of the iron core silicon steel sheet multiply the quality of the silicon steel sheet. In general, its loss is very small. For example, the S9-100/10 distribution transformer has a no-load loss of 290W. The larger the transformer capacity, the smaller the no-load loss, generally between 0.3-0.15% of the rated capacity. However, the transformer works continuously for 24 hours, and this loss cannot be ignored. The load loss: The short-circuit of the coil on the secondary side apply the rated current at the rated frequency on the primary side. The transformer loss at this time is the loss of the transformer coil and the iron core. Let's take the S9 series transformer as an example and see its load loss value:The load loss of S9-100/10000 transformer is 1500W.The load loss of S9-1000/10000 transformer is 10300W.The load loss of a transformer is generally between 0.9-1.8%. The larger the transformer, the smaller the load loss.V Guide to What You Maybe Interested in 5.1 How to Install Low Voltage Transformer for Household? First, make sure you have an outlet available. Most family homes will have several outdoor power outlets installed. Second, think about the layout of the lighting. It is important to plan ahead when installing low voltage lighting so that you can avoid any potential problems, especially with the setup.Third, choose a transformer.①Magnetic or Electronic.②Make sure to buy a transformer that can handle the lighting load you need it to.Fourth, install the transformer. Transformers are installed simply by plugging them into your outdoor outlet.5.2 How to Troubleshoot a Low-Voltage Transformer(1) First, check whether there are obvious abnormalities by observing the appearance of the transformer: such as whether the coil lead is broken, whether the insulating material has scorch marks, whether the fastening screw of the iron core is loose, whether the silicon steel sheet is rusted, and whether the winding coil is exposed Wait. (2) Test a transformer with a digital multimeter, open all secondary windings, put the multimeter in the AC block (500mA, in series into the primary winding). When the plug of the primary winding is inserted into the 220V AC mains supply, the multimeter indicates the no-load current value. This value shall not be greater than 10% - 20% of the full load current of the transformer. Generally, the normal no-load current of the power transformer of common electronic equipment should be about 100mA. If too much is exceeded, the transformer has a short-circuit fault. Low Voltage Electronic Transformer Troubleshooting Guide5.3 Repairing a Transformer(1) Understand the reasons for the problem. Generally, a transformer has failed due to some fault in the electrical circuit.(2) Check the replacement transformer. If the short circuit is caused by component failure, the new transformer may still burn out. If you replace the transformer, examine it to make sure that the incident will not occur again.(3) Check the condition of the external fuse. If the transformer has an internal fuse, there may not be a fuse on the power line. On the contrary, the device must be protected by a fuse mounted on the power circuit. Check whether the fuse is intact and replace the faulty fuse.(4) Check the secondary power consumption. Sometimes, this kind of consumption is very high, which leads to equipment failure. If the transformer has multiple ratings and the multimeter shows the value "OL" during the measurement, it may be a short circuit in the secondary winding.5.4 Malfunction of Factory Low Voltage Transformer(1) Abnormal sound in transformerThe abnormal sound inside the transformer may be caused by the following reasons:①Heavy overload causes buzzing sound inside the transformer; ② Due to poor internal contact or breakdown point, the transformer occurs crackle sound③ Some parts of the connection shaft and the core of the transformer are loose, which causes the silicon steel sheet to vibrate④ When there is a grounding or short-circuit fault in the power grid, a large current flows through the winding, which will produce strong noise⑤ The iron core, the winding discharges to the shell, or the core ground wire is disconnected. All these can make the transformer discharge sound. (2) The oil level of the transformer is too high or too lowUnder normal circumstances, the changes in oil temperature can cause a change in oil level. As the oil temperature changes, the oil level also changes accordingly. However, under abnormal conditions, abnormal oil levels can also be caused by faults such as oil seepage and water seepage and other accidents. Second, the change in oil temperature is related to load conditions, ambient temperature and other conditions. When the change of oil level is inconsistent with these elements, it may be a false oil level. (3) Transformer oil quality has deteriorated or oil temperature has suddenly increasedIn working condition, the main function of transformer oil is cooling and insulation. When running overheated for a long time or if water enters the casing and absorbs moisture, the oil quality will deteriorate. Through the oil mark, we can found  that the oil color is abnormally deepened or blackened. Through sampling and analysis, it can be detected that the oil contains carbon particles and moisture, the acid value increases, the flashpoint decreases, and the insulation strength decreases. This situation can easily lead to serious accidents. A sudden rise in oil temperature when the transformer is operating normally is often related to the overheating inside the transformer. The iron core catches fire, the internal screws are loose, the cooling device is faulty, the transformer is heavily overloaded, all may cause the oil temperature to rise suddenly. (4) Transformer on fireWhen the transformer is out of order and it is not handled in time, it may catch fire. When the transformer is on fire, the insulating oil burns and turns into gas, which makes the oil tank burst. The burning insulating oil sprays out of the transformer, which will cause equipment damage and property loss. The short circuit inside or outside the transformer wire, severe overload, a lightning strike may cause the transformer to catch fire.VI One Question Related to Low Voltage Transformer6.1 Question (Multiple choice questions)The winding of wire around a core which is connected to a source of energy is called the ______ coil.primarysecondarytertiary6.2 AnswerA、B  VII FAQ1. What are low voltage transformers?A low voltage transformer is at the heart of every landscape lighting system. It converts 120-volt current to a low voltage current (between 12-15 VAC). ... Magnetic transformers use two coils to reduce the voltage from 120 volts down to 12 volts. 2. What low voltage transformer do I need?Transformers generally range from 150- to 900-watt capacity. Matching the size of the transformer to the lighting design is important for the efficient operation and function of the system. House current, 120 volts, is reduced by a transformer to 12 to 20 volts, the current needed to operate low-voltage landscaping lights. 3. What are low voltage transformers used for?Low Voltage Transformers Low voltage transformers are power transformers that are used to change the voltage capacity of a low-voltage electrical transmission line. Typically, electronic low voltage transformers convert 120 volts into 12 volts or 24 volts. 4. How do you test a low voltage transformer?• Identify the transformer's terminals, using its label as a guide. • Turn a multimeter to its VAC function. • Test the transformer's input voltage with the multimeter, using the transformer's label as a terminal guide. • Test the transformer's output voltage with the multimeter. 5. How long do low voltage transformers last?20 to 25 years.They operate at about 90 to 95 percent efficiency and can run for a very long time, anywhere from 20 to 25 years. They also are much quieter, so you can place them close to the fixtures, rather than having to run wires a long way from the transformer to the fixture itself. 6. Can I plug a low voltage transformer into an extension cord?One warning though to be observed is to never use an extension cord between the transformer and the electrical outlet. Always plug the transformer directly into the power outlet. As you can see, low voltage outdoor lighting is not all that hard to install or maintain. 7. Can you hardwire a low voltage transformer?To hardwire a low voltage transformer, the main power should be turned off at the breaker panel before making any electrical connections. ... The polarity of these wires is not important; either wire on the output side of the transformer may be connected to either wire of the low voltage circuit. 8. Do you need a transformer for low voltage lighting?When operating low voltage lights, you need a transformer to convert your standard line voltage (120V or 277V) into low voltage (12V or 24V). This allows your lights to function properly. If you connect low voltage lights directly to line power, the higher voltage would cause them to burn out immediately. 9. How do you tell if a transformer is going bad?Symptoms of power quality issues include vibration, excessive buzzing or humming and overheating. Technicians should occasionally check the power of transformers that supply nonlinear loads, such as variable frequency drives (VFDs) or switching power supplies. 10. Can you replace a transformer with a light fitting?They will have a transformer either in the ceiling or light fitting. Some LED bulbs, like the Philips Master LED range, have in-built circuitry that can deal with most (but not all) transformers, so you don't have to change them. In other cases, you need to replace the transformer with an LED driver. 

Ⅰ IntroductionA differential transformer is an electromagnetic inductive displacement sensor that converts mechanical displacement into an electrical signal. It mainly relies on the displacement of the movable iron core in the cylindrical coil and establishes a mutual induction relationship between the input coil and the output coil of the cylindrical coil, and the displacement of the movable core can be obtained by measuring the induced voltage of the output coil proportional to it.  CatalogⅠ IntroductionⅡ The Working Principle and Structure of the Differential TransformerⅢ The Type of Differential TransformerⅣ Linearity and SensitivityⅤ The Cause of the ErrorⅥ The Measurement Circuit  6.1 Differential DC output circuit  6.2 DC differential transformer circuitⅦ The Application of Differential TransformerⅧ Application Circuit Examples of Differential Transformer  8.1 MZK-4R Grinding Machine Automatic Control Device  8.2 ZD41B Short Cylindrical Roller Sorting Machine  8.3 Discussion of Differential Transformer ApplicationⅨ FAQ Characteristics of Differential Transformer(1) There are many types of linear ranges, and it is easy to select according to the use. Usually, there are about 10 types between ±2 mm and ±200 mm.(2) The structure is simple, so the vibration resistance and impact resistance are strong.(3) It does not wear, does not deteriorate, and has excellent durability.(4) The output voltage has a precise ratio to the displacement of the core, that is, the linearity is good. Generally, the full stroke deviation of this sensor is less than 1%, and it can be guaranteed to be ±0.2% to ±0.3% in high-grade products.(5) Because of the high sensitivity, a large output voltage can be obtained, and a small displacement can be detected without requiring an advanced circuit.(6) Since the output changes smoothly, high-resolution detection is possible.(7) The zero point is stable, and its use as a reference point for measurement is good for maintaining accuracy.(8) A high response speed from 500 Hz to 100 Hz can be obtained. Ⅱ The Working Principle and Structure of the Differential TransformerThe structure of the differential transformer is divided into two types: variable-gap type and solenoid type. Since the variable-gap type differential transformer has a small stroke and a complicated structure, it is rarely used at present, and the solenoid type is usually adopted. The basic components of the solenoid type differential transformer include an armature, a primary coil, a secondary coil, and a coil frame. The primary coil acts as excitation and corresponds to the primary side of the transformer. The secondary coil is formed by inverting two coils of the same structural size and parameters to form the secondary side of the transformer. There are two-section, three-section and multi-section according to the initial and secondary arrangement. The zero potential of the three-section is small, the two-section is more sensitive than the three-section, and the linear range is large. The four-section and five-section are all efforts to improve the linearity of the sensor. The working principle of the differential transformer can be explained by the principle of the transformer. The difference is: the general transformer is the closed magnetic circuit, and the differential transformer is the open magnetic circuit; the mutual inductance of the original transformer and the secondary side is constant, and the mutual inductance between the primary and secondary sides of the differential transformer changes as the armature moves. The operation of the differential transformer is based on the change of mutual inductance. The construction principle of the differential transformer is as shown in figure 1, and is composed of a cylindrical coil and a core that is completely separated from it. A typical differential transformer has three cylindrical coils, each of which is one-third of the total length, with a primary coil in the middle and a secondary coil on each side. The iron core added to the cylindrical coil is used to link the magnetic lines of force in the coil to form a magnetic circuit. Figure 1. The Construction Principle of the Differential Transformer When an alternating voltage is applied to the primary coil in the middle (ie, excitation), an electromotive force is generated due to the mutual inductance with the coils at both ends (this is the same as that of a normal transformer). Since the secondary coils are connected in series with each other in opposite polarity, the induced electromotive forces in the two secondary coils are opposite in phase, and as a result of the addition, a potential difference between the two is generated at the output end. At the center of the coil length direction, the induced voltages of the two secondary coils are equal in opposite directions, and thus the output is zero. This position is called the mechanical zero point of the differential transformer (or simply zero points). When the iron core changes position from zero points to a certain direction, the voltage of the secondary coil in the displacement direction increases, and the voltage of the other secondary coil decreases. The product design guarantees that the potential difference is proportional to the displacement of the core. When the iron core moves from zero points to the opposite direction, a proportional voltage is generated, but the phase is 180° different from the previous one. The relationship between the secondary coil voltage and the output voltage difference with respect to the core displacement is shown in figure 2. The range in which the voltage difference is proportional to the core displacement is called the linear range, and its proportionality is called linearity, which is the most important indicator of the differential transformer. Figure 2. The Core Displacement — Output Relationship of Differential Transformer Ⅲ The Type of Differential TransformerThe standard differential transformer consists of a cylindrical coil and a rod-shaped iron core. In actual use, there is also a structure with a guide and a spring. The basis for the classification of differential transformers is as follows: • According to the voltage input to the primary coil(excitation type)Commercial power supply type is suitable for practical measuring instruments of 50-60Hz, 6.3V power supply excitation;Oscillation power supply type is an excitation circuit of 1~5KHz, it is suitable for application measuring instruments requiring certain accuracy and response characteristics;DC power supply type, the semiconductor device is installed in the coil part of the differential transformer to form the excitation oscillation circuit and the secondary output detection circuit inside the coil. It is a differential transformer whose input and output are both DC, called DC-DT. • According to the displacement range of the iron core (displacement type)Small displacement type considers how to measure the small displacement below 0.5mm from the structure;General displacement type is designed for measuring the displacement about 100mm or less;The long-stroke type is designed for long stroke measurement of 120 to 400 mm.  • According to the use environment (environment type)Standard type is used in a normal environment with a temperature of -30℃ to +90℃ and a humidity of about 80%;Environmentally friendly type is the sensor for high temperature, high humidity, waterproof and radioactive environments. Features and SpecificationsWhen using a differential transformer as a position sensor, the selected specifications are as follows:◆ Excitation power supply (frequency, voltage, waveform, etc.);◆ Structure (whether guides and springs are required);◆ Linear range (it is usually ±1%, and that of high-grade products is ±0.5%～±0.2%);◆ Sensitivity (corresponding to the output of the core displacement of 1mm);◆ Impedance (input, output impedance);◆ Connection conditions (cables, sockets, input circuits, etc.);◆ Assembly method (connection method with the object to be tested, etc.);◆Environmental conditions (temperature, humidity, dust, water resistance, rust-proof conditions, etc.). Ⅳ Linearity and Sensitivity• Linearity. The linear range of the differential transformer is affected by the non-uniform magnetic field of the solenoid coil. A reasonable design guarantees the required linear range and linearity.• Sensitivity. The sensitivity of the differential transformer refers to the change of the output potential generated by the armature unit displacement. It can be expressed by mV/mm. In practice, considering the influence of the excitation voltage, it is also commonly expressed by mV/mm/V, that is, the potential change generated by the armature unit displacement divided by the excitation voltage value. The sensitivity of the differential transformer is related to the primary voltage, the number of secondary winding turns, and the frequency of the excitation voltage:• Relationship with secondary turnsThe number of secondary turns increases and the sensitivity increases, which is linear. However, the number of secondary turns cannot be increased indefinitely because the residual voltage at the zero points of the differential transformer also increases.• Primary voltageThe sensitivity is proportional to the primary voltage, but the primary voltage should not be too large. When the voltage is too large, the differential transformer coil will heat up and cause the output signal to drift. Generally, 3~8V is used.• Excitation power frequencyWhen the frequency is very low, the sensitivity increases with increasing frequency; when the frequency increases, the inductance of the coil is much higher than its resistance, the sensitivity is independent of the frequency; when the frequency exceeds a certain value (the value varies depending on the armature material), the effective resistance of the wire increases due to the skin effect of the wire at a high frequency, and the eddy current loss and hysteresis loss of the armature increase, and the output decreases. Figure 3 is the relationship between the input frequency and sensitivity of a certain magnetically permeable material, which can be used as a reference for selecting the excitation frequency. Figure 3. Relationship Between Excitation Frequency and Sensitivity of Differential Transformer Ⅴ The Cause of the ErrorThe error refers to the deviation between the actual and ideal characteristics of the sensor. Here, the system error inherent in the sensor itself and random error is mainly analyzed, and the error in the measurement method is not involved.• Influence of amplitude and frequency of excitation power supplyFluctuations in the magnitude of the excitation supply voltage cause changes in the strength of the excitation field of the coil to directly affect the output potential. The frequency fluctuations have little effect.• The effect of temperature changesChanges in ambient temperature cause changes in the magnetic permeability of the coil and the magnet, causing a change in the magnetic field of the coil to cause temperature drift. This effect is more severe when the coil quality factor is low. The use of constant current source excitation is more advantageous than the constant voltage source. Properly increasing the quality factor of the coil and using a differential bridge can reduce the effects of temperature.• Zero residual voltageWhen the armature of the differential transformer is in the neutral position, the ideal output voltage should be zero. But in fact, when using a bridge circuit, there is always a small voltage value (from a few millivolts to tens of millivolts) at zero point, which is called the zero residual voltage. Figure 4 is an enlarged output characteristic of the zero residual voltage. The dotted line is the ideal characteristic and the solid line indicates the actual characteristics. The presence of a zero residual voltage causes an insensitive zone near the zero point. Figure 4. Zero Residual Voltage of the Differential TransformerThe waveform of the zero residual voltage is very complicated and irregular. It is analyzed to include the fundamental wave in-phase component, the fundamental wave orthogonal component, and the second and third harmonics as well as the electromagnetic interference waves with small amplitude. The reasons why the zero residual voltage is generated are as follows:• Fundamental wave component: Since the winding of the two secondary windings of the differential transformer can not be completely identical in process, its equivalent circuit parameters (mutual inductance, self-inductance and loss resistance, etc.) cannot be completely equal, thus two induced potential values are not equal. The copper loss resistance of the primary coil, the iron loss and material non-uniformity of the magnetically permeable material and the presence of the inter-turn coil capacitance cause the excitation current to be out of phase with the generated magnetic flux.The above factors cause the induced potentials in the two secondary coils to be not only unequal in value but also in phase. The zero residual voltage generated by the difference in phase cannot be eliminated by adjusting the armature displacement. • High-order harmonics: The high-order harmonics are mainly caused by the nonlinearity of the magnetization curve of the magnetically permeable material. Due to the effects of hysteresis loss and magnetic saturation, the excitation current is inconsistent with the magnetic flux waveform, resulting in a non-sinusoidal wave (mainly the third harmonic flux), thereby inducing a non-sinusoidal potential in the secondary winding. The general method for eliminating zero residual voltage:— From the design and process, try to ensure the symmetry of the coil and the magnetic circuit. The structure can adopt the magnetic circuit adjustment mechanism; when selecting the working point of the magnetic circuit, it should be ensured that the magnetic field does not work in the saturation region of the magnetization curve.— Use the appropriate measurement line. The phase-sensitive detection circuit can not only identify the moving direction of the armature but also eliminate the high-order harmonic zero residual voltage of the armature in the middle position. As shown in figure 5, after using the phase-sensitive detection, the characteristic curve of the armature reverse stroke changes from 1 to 2, thereby eliminating the zero residual voltage. Figure 5. Output Characteristics After Phase-sensitive Detection— Use compensation lines. In applications of a differential transformer, there are many circuit types used to eliminate the zero residual voltage, which can be summarized as follows:▲Add series resistors to eliminate the in-phase component of the fundamental wave; generally the resistance of the series resistor is very small such as 0.5~5Ω, and is wound with constant wire.▲Add parallel resistors to eliminate the fundamental wave orthogonal component, but it has an effect on the in-phase component of the fundamental wave; the resistance of the shunt resistor is from tens to hundreds of kiloohms.▲Shunt capacitor, change phase shift, and compensate for high-order harmonics; parallel capacitor value is in the range of 100 ~ 500pf.▲Add feedback winding and feedback capacitor to compensate for fundamental wave and high-order harmonics.In fact, these values are determined experimentally; based on the working principle of the differential transformer and the cause of the zero residual voltage, the above methods can be modified and combined, and it is also possible to design a new compensation circuit. Figure 6 shows some line schematics for compensating for zero residual voltage for reference. Figure 6. Zero Residual Voltage Compensation Circuit of Differential Transformer Ⅵ The Measurement Circuit6.1 Differential DC output circuitThe output voltage of the differential transformer is an AC signal whose amplitude is proportional to the armature displacement. If the output value is measured with an AC voltmeter, it can only reflect the magnitude of the armature displacement and cannot reflect the direction of the displacement. Secondly, there is a certain zero residual voltage in the AC voltage output. Even with various compensation methods, it can only be reduced and cannot be completely eliminated. Therefore, the DC output circuit is commonly used in engineering practice, which can reflect the displacement direction of the armature and compensate for the zero residual voltage. The DC output circuit has two forms: one is a differential phase-sensitive detector circuit, and the other is a differential rectifier circuit.The differential rectifier circuit is shown in Figure 7. This circuit is relatively simple. It does not need to compare the voltage windings. It does not need to consider the influences if the phase adjustment and the zero residual voltage. The influence on the sensing and distributed capacitance can also be ignored. In addition, since the rectifying portion is on the differential output side, the two DC conveying lines are convenient to connect, and can be transported at a long distance, and are widely used. Figure 7. Differential Rectifier Circuita) full-wave current output         b) half-wave current outputc) full-wave voltage output         d) half-wave voltage outputDifferential phase sensitive detector circuits come in many forms. Figure 8 shows two examples, one is a full wave circuit and the other is a half-wave circuit. The phase sensitive detector circuit requires that the comparison voltage and the secondary transformer output voltage of the differential transformer have the same frequency and the same phase or opposite phase.  To ensure this, a phase-shifting circuit is usually connected to the circuit. In addition, it is required that the comparison voltage amplitude should be as large as possible (because the comparison voltage acts as a switch in the detector circuit, and if it is less than the signal voltage, the switch cannot be turned on), generally it should be 3 to 5 times the signal voltage. In the figure, Rw is the bridge zero potentiometer. For the case of measuring small displacements, since the output signal is small, the input amplifier is also connected to the circuit. Figure 8. Differential Phase-sensitive Detection Circuita) full-wave detection         b) half-wave detection6.2 DC differential transformer circuitThe working principle of the DC differential transformer is exactly the same as that of the ordinary differential transformer described above. The only difference is that the power supply used in the instrument is a DC power supply (dry battery, battery, etc.). The schematic diagram of the DC differential transformer is shown in figure 9. It consists of a DC power supply, a multivibrator, a differential rectifier circuit, a filter and so on. Figure 9. Schematic Diagram of DC Differential Transformer CircuitThe multivibrator provides a high frequency excitation power supply for the differential transformer, which can be a square wave, a triangular wave or a sine wave. DC differential transformers are commonly used in the following applications:◆ The measuring point is far from the control room (more than 100m);◆ Simultaneous use of multiple differential transformers and requires no interference with each other and with other equipment;◆ Where explosion protection is required;◆ Requires easy to carry, such as working in the field. Ⅶ The Application of Differential TransformerDisplacement measurement is the most important use of differential transformers. Any physical quantity that can be transformed into a displacement can be measured with a differential transformer. It is noted that the differential transformer measurement is generally contact type. In some cases, it will affect the state of the measured object (such as vibration), which is the so-called “load effect”. In this case, other types of sensors must be used such as eddy current sensors, etc.◆ It can be used as the main component of many precision measuring instruments, such as making high-precision inductance comparator with corresponding measuring devices, which can perform various precise measurements on parts: length, inner diameter, outer diameter, non-parallelism, non-flatness, non-perpendicularity, vibration, eccentricity, and ellipticity.◆ As the main measuring part of the bearing rolling element automatic sorting machine, it can sort large and small steel balls, large and small cylinders, large and small round vertebrae, needle roller and so on.◆ It is used to measure the expansion, elongation, strain, movement, etc. of various parts. With a variety of sensors, its displacement measurement range can be from ±3μm to over 1000mm.◆ Vibration and acceleration measurements. An accelerometer for measuring vibration can be constructed by using a differential transformer and a cantilever beam elastic support.◆ Pressure measurement. The differential transformer and the elastic sensitive component (diaphragm, bellows, spring tube, etc.) can be combined to form a pressure sensor of the open-loop system and a force-balanced pressure gauge of the closed-loop system. Due to the excellent characteristic of differential transformer as the displacement sensor, it has been applied in almost all industrial fields and several specific examples are described below.• Steel industry: blast furnace top-level detection, continuous casting roll gap, sand type vibration, convexity detection, position detection of sliding water nozzles such as ladle and tundish.• Heavy motor industry: the main valve of the steam turbine, the valve lift detection of the bypass valve, and the posture monitoring of the elevator.• Construction machinery industry: Measuring head for numerical control machine tool simulation test.• Ceramic industry: thermal expansion testing of refractory materials, shape detection of templating glass.• Ship and vehicle industry: fuel classification position detection of diesel engine, dynamic characteristic detection of fuel injection valve of an automobile engine, and eccentricity detection of tire and wheel.• Weighing machine industry: a device that automatically measures the weight of the bag, and a weighting machine for the asphalt carrying device.• Measuring instrument, testing machine industry: used for traction test, creep test of metal materials and plastics, signal conversion part of flow meter and liquid level meter, a mechanical test of civil building components.• General industry: spacer separators for assembling bearings, motion deviation detection during stamping, and measurement of workpiece size and shape deviation. Ⅷ Application Circuit Examples of Differential Transformer8.1 MZK-4R Grinding Machine Automatic Control DeviceThis device is used on automatic or semi-automatic grinding machines. During the grinding process of the workpiece, the control device can accurately output 4 signals according to the amount of the pre-regulation to control the introduction of the grinding head, rough grinding, fine grinding, light grinding and exit, etc., thus realizing the automatic measurement and control of the grinding process. • Working process of the grinding machineWhen the workpiece is loaded, the measuring device first enters the workpiece for measurement. If the workpiece size meets the pre-adjusted result, the control device sends a “starting” signal, the grinding head enters the workpiece and moves forward quickly to the machining direction, and coarse grinding starts. Taking the internal grinding as an example, as the workpiece size of the grinding wheel becomes smaller, the output signal of the measuring head also becomes smaller.  When the preset position is reached, the trigger sequentially sends three signals, that is, the “rough grinding end” signal, indicating that the rough grinding is finished, so that the moving speed of the grinding wheel is reduced, and the fine grinding starts; when the fine grinding is finished, the “finishing end” signal is issued, so that the grinding wheel stops moving and the light grinding starts; when the preset size is reached, the “light grinding end” signal is issued to make the grinding wheel and the detection device exit quickly. • Working principle of measuring head (sensor)The measuring head adopts a differential transformer type displacement sensor, and its structure is as shown in figure 10(a). The iron core moves to the right, so that the induced potential of the winding A decreases, and the induced potential of the winding B increases (and vice versa). The two windings and the resistors R1 and R2 in the measuring device form a bridge to realize differential output, as shown in figure 10(b). Figure 10. Schematic Diagram of the Differential TransformerThe primary coil is excited by a square wave generator with a square wave frequency of 3 kHz and an effective voltage value of 3.5V. Along with the change of the displacement of the core, a corresponding voltage variable is generated between the boom of the potentiometer Rw and the secondary common tap (ground) of the measuring head. The displacement-voltage characteristic curve in figure 11 is obtained after the voltage variable is amplified and phase-sensitive rectified. Figure 11. Output Characteristic Curve of Differential TransformerIn the figure, the S-T segment is the full linear range, wherein the H-E segment (high precision) is the ×1 gear indication range, and the K-C segment (low precision) is the ×10 gear indication range. The“start”signal 0 is sent in the D-A segment, the“rough grinding end” signal 1 is sent in the G-B segment, and the“fine grinding end” signal is 2 sent in the 0-F segment. The“light grinding end”signal 3 is sent at point 0. • Principle of the circuit①The circuit block diagram shown in figure 12. Figure 12. Circuit Block Diagram of Control Device②Explanation of the circuit principleThe device consists of six parts: ▲Input bridge, the two arms are composed of two secondary windings of the measuring head, the other two arms are composed of R84 and R85, the potentiometer VR1 is used for the electrical zero points coarse adjustment, the VR2 is used for the zero points fine adjustment, and the R86 is used to limit the zero point adjustment range.In order to obtain the reference voltage for amplifier calibration, a voltage is obtained by the square wave generator, and another bridge is formed by transformers TR4, R88, and R89, and VR4 is used to adjust the reference voltage. ▲The amplifier amplifies the weak signal obtained in the input circuit to have sufficient amplitude to complete the measurement and control. T15, T17, and T18 form a voltage amplifier with gains of about 10, 20, and 20 dB, respectively. T16 is a buffer stage. T19 and T20 form a push-pull power amplifier stage, and the voltage gain of the amplifier is about 60 to 70 dB. In order to achieve higher stability and linearity, deeper negative feedback is added to each stage. The negative feedback of first stage is adjustable, and the total gain of the amplifier is adjusted by VR3. ▲Phase-sensitive rectification and indicating circuit are used to complete the rectification and identify the phase of the input signal. The half-wave rectification circuit is composed of D15 and D16, and the blocking voltage is 13V, which is provided by the square wave generator.The rectified DC ramp signal is used as an input to the trigger on the one hand and as a panel indicator on the other. The μ meter is a microampere meter with a full-scale of 150μA, and full-scale indications of 50μ and 500μ are obtained with shunt resistors R90 and R91. D33 is used as a voltage clamp to protect the meter head. ▲Square wave generator, which is used to generate the excitation voltage required by the measuring head and the blocking voltage required for phase-sensitive rectification. The high rectangular coefficient multivibrator circuit is composed of T21 and T22, which is easy to start, high in frequency and amplitude stability, and its oscillation frequency is 3 to 3.5 kHz. ▲Trigger, according to the comparison of the output voltage of the phase-sensitive rectification and the pre-adjustment voltage, four different control signal outputs are sequentially generated. The circuit adopts a trigger with an emitter coupled by a Zener tube, which has a small temperature drift and convenient backlash adjustment. Among them, VR5, VR6, VR7, and VR8 are used as the adjustment potentiometers for the four signals of “0”, “1”, “2”, and “3” on the panel. ▲Power:-24V, used for power relay after rectification and filtering;-15V, generated by the series regulator circuit and is used as the collector voltage of each transistor and the trigger pre-call;+6V, generated by the shunt regulator circuit and is supplied for the bias and pre-call of the trigger. • Main technical indicators✿ Instrument indexing and error:High precision (G) 1μ/division; full scale -10～+50μ; error ≤1.5μLow precision (D) 20μ/division; full scale -100～+500μ; error ≤30μ✿ Adjustable range of control signal :Signal "0", 350～500μ;Signal "1", 30～100μ;Signal "2", 0 ~ 30μ;Signal "3", -10 ~ +10μ✿ Electrical zero adjustable range:Not less than 100μ, and ±5μ fine adjustment✿ Repeat error:No more than 1μ✿ (Grid) voltage adjustment error:No more than 3μ✿ Instability:Time drift is no more than 10μ/4 hours; temperature drift is no more than 10μ/ 10℃ 8.2 ZD41B Short Cylindrical Roller Sorting MachineThis machine is composed of high-precision micrometer (differential transformer), combined with transistor circuit to form measurement and logic control device to complete the task of automatically sorting short cylindrical bearing rollers. • Main technical indicators◆ Measurement range:length is no more than 15mm5 to 15 mm in diameter◆ Accuracy:1μ, 2μ, 3μIf the magnification and radial grouping potentiometer are re-tuned, any grouping in the range of 0.5 to 5μ can be obtained.◆ Number of groups:10 groups.◆ Speed:28/min to 65/min,can be adjusted arbitrarily • Working principleThe measurement and classification of the radial dimensions of the roller are automated. The roller to be tested is manually placed in a disc-shaped hopper, passed through the vibrating roller to the feeding position along the pipe, and then pushed into the measuring portion by the reciprocating push rod for radial measurement. When different sizes of rollers enter the measurement site for measurement, the differential transformer guide core is displaced in the coil, so that the differential transformer outputs an alternating current signal proportional to the change in the size of the roller, and tiny electrical signal is amplified, rectified, and then amplified by the DC amplifier, so that the corresponding trigger drives the relay and the electromagnet to open the storage valve of the sorting group, so that the measured rollers of different diameters are placed in different sorting bins for automated measurement and sorting. Here we mainly introduce the radial dimension measurement part, namely the differential transformer and its secondary circuit. The measuring part of the roller consists of a differential transformer, a 4KHz oscillator, an attenuator, a low-frequency AC amplifier, a phase-sensitive rectification, a DC amplifier, a regulated power supply, etc. ① Micrometer (differential transformer): The differential transformer is used to convert the diameter of the roller into a change in the amount of electricity. The primary coil is excited by a rectangular wave with a frequency of 4 kHz and an amplitude of 2 to 3 volts. Thus, the voltages of u2 and u3 are induced in the secondary coil. The different names of the secondary coils are connected as a common point ground, and the other ends serve as a differential output and form a bridge balance loop with the resistors R1, R2 and the potentiometer VR.  When the iron core is at the center position of the two secondary coils, since the magnetic resistance of the two coils is equal, the bridge is in a balanced state, and the differential transformer output E2=0 (u2=u3). In a static state, due to the self-weight of the iron core and the guide rod, the iron core is located at the lowermost end of the secondary coil, thus outputting a negative polarity voltage; when the roller is measured, the guide rod is displaced upward, and the iron core is also displaced upward in the differential coil. The output voltage varies with the displacement. When the displacement exceeds the center position, the differential transformer outputs a positive voltage. ② Oscillator: A high-frequency triode is used as a capacitive voltage divider oscillator with an oscillation frequency of 4KHz. This circuit feature avoids the difficulty of inductive oscillator winding. The intermediate transformer is used to couple the output, and then through the first-stage voltage amplification, the two pairs of Zener diodes are used to limit the clipping to form a rectangular wave with constant amplitude (2~3V), one way is for the primary excitation of the differential transformer and the other is for the phase-sensitive rectification comparison voltage. ③ AC amplifier: three-stage amplification circuit and transformer-coupled output. In order to keep the amplifier gain stable, 20dB negative feedback is introduced between the first and second stage, and the total gain is 75~80dB. ④ Phase-sensitive rectifier circuit: diode half-wave phase-sensitive rectification is used, the comparison voltage amplitude is high, and both diodes are turned on in the positive half cycle. The signal voltage is small, the positive voltage is output in the same phase with the comparison voltage, and the negative voltage is output in the opposite phase with the comparison voltage. ⑤ DC differential amplifier: The DC voltage output from the phase-sensitive rectifier circuit is further amplified and the polarity is converted. When inputting ±50mV, the differential output is 4~12V. 8.3 Discussion of Differential Transformer Application(1) The above example uses the two directions of the differential transformer and is determined for the special purpose of roller sorting. When measuring with a roller of nominal size, the differential transformer core is just adjusted to the center position, the positive tolerance roller produces a positive displacement, and the positive voltage is output; the negative tolerance roller produces a negative displacement and outputs a negative voltage. This makes full use of the linear range of the differential transformer. For different applications, especially for small-range, high-precision measurements, there is no need to distinguish the direction of the displacement. It is also possible to use only the displacement of the differential transformer in one direction, and the corresponding circuit can be simplified. (2) This product was a product of the 1970s, so a transistor discrete component circuit was used. Today's electronic technology and the component levels are no longer the same. AC amplifiers and DC amplifiers can be used with operational amplifiers, and performance is much better than discrete component circuits. The basic principles of the circuit and the various functional parts are still applicable and can be designed accordingly. (3) Nowadays, the application of single-chip microcomputers can completely replace the various logic circuits in the past. In the case of a single-chip microcomputer, the entire circuit design may vary greatly. For example, the oscillation source can be digitized (crystal oscillator frequency division may be directly generated by a single-chip microcomputer), and the measurement result is digitized (via A/D conversion), and a large number of analog comparators, triggers can be replaced by program judgment methods.  Furthermore, with the precise timing and synchronization function of the single-chip microcomputer, A/D conversion can be directly performed on the AC signal sampling, and the phase-sensitive rectifier circuit can be omitted. After the measurement results are digitized, data transmission can be used instead of analog transmission, thus precision will not be lost, interference will not exist and transmission distance will be long. Ⅸ FAQ1. Why does LVDT use high voltage?It is a type of electrical transformer used for measuring linear displacement.The linear variable differential transformer has three solenoidal coils placed end-to-end around a tube. The center coil is the primary, and the two outer coils are the top and bottom secondaries. A cylindrical ferromagnetic core, attached to the object whose position is to be measured, slides along the axis of the tube. An AC current drives the primary and causes a voltage to be induced in each secondary proportional to the length of the core linking to the secondary.Cutaway view of an LVDT. Current is driven through the primary coil at A, causing an induction current to be generated through the secondary coils at B. When the core is displaced toward the top, the voltage in the top secondary coil increases as the voltage in the bottom decreases. The resulting output voltage increases from zero. This voltage is in phase with the primary voltage. When the core moves in the other direction, the output voltage also increases from zero, but its phase is opposite to that of the primary. The phase of the output voltage determines the direction of the displacement (up or down) and amplitude indicates the amount of displacement.  2. What are the advantages of using an LVDT?• Very reliable: Long sensor lifespan due to near frictionless operation of most models.• Very high resolution: Because of the near-frictionless movement they provide virtually infinite resolution. Even the smallest changes can be detected.• Damage resistant: In some models, both ends of the tube are open, preventing sensor damage if the test article pushes the rod farther than expected (except for collision with the tube itself).• Null point stability: The zero or null point of the sensor is extremely repeatable due to the construction of the sensor itself.• Wide range of operating temperatures: There are LVDT models available that can withstand cryogenic temperatures (-200℃/ -328℉) as well as high temperatures (650℃/ 1200℉)• Low hysteresis/ high positional accuracy and repeatability• Absolute reading output device: As opposed to an incremental output device, the reading from an LVDT will be the same before and after its power is cycled (assuming that the object under test did not move).  3.What are the disadvantages of using an LVDT?• Limited measurement distance: Even the largest LVDTs are limited to less than 1m (~27'') measurement ranges.• Can be affected by magnetic fields (models with shielding are common as a result).• AC models require a precise AC excitation from an LVDT signal conditioner.• DC LVDT models have an inferior shock, vibration and temperature specifications compared to AC LVDT models. 4. How do I interface an LVDT output with PLC?The output is voltage so you will need an analog input card which can take in a voltage input and then inside the PLC you will scale what that voltage corresponds to. For eg 10 V could mean 10 mm or 10 degrees etc. If the output is current them you would need an analog IP card which accepts current. Most common current used is 4–20 mA. 5. What are the applications of the Bourdon tube and the LVDT method for pressure measurement?A bourdon tube is a curved, hollow, closed end tube which can be pressurized. The pressure will attempt to straighten out the tube as it is increased. The amount of movement is typically very small but can be mechanically amplified. The translation of the end of the tube can be a linear indication of the pressure applied to the other end.Pressure gauges have used this technique for over a century and a half to indicate pressure manually on a dial gauge with a linkage that moves a dial pointer.To make electronic readouts of pressure to remote dials or to computers, a linear movement to electrical voltage is needed. An LVDT satisfies this need. An LVDT is a variable transformer consisting of a movable magnetic core sliding inside a tube with a primary and secondary winding. As the core is displaced the coupling between windings is varied linearly. If a small AC voltage is applied to the primary then the amplitude of the secondary output can be measuered in amplitude to indicate proportional to the pressure.So this makes a hybrid sensor or transducer, pressure to displacement connected to a displacement to variable voltage resulting in a pressure to variable voltage device.Technically this is an older way of converting pressure to volts… and is subject to hysteresis or mechanical backlash. Most modern P-V transducers use strain gauge bridge followed by an instrumentation amplifier to have fewer moving parts and less hysteresis. 6. Discuss various applications where LVDT’s can be used?They can be used in any application where a highly accurate measurement of linear displacement or position is needed. This includes precision gaging systems for measurement and metrology, feedback transducers for precision servomechanisms, torque, force and moment transducers, materials testing equipment (tensile testers, rheometers, fatigue testers, etc.). 7.What is the accuracy of a LVDT and an inductance transducer in a displacement measurement?Accuracy for both devices depends on the way they are designed, made and used, and the materials from which they are made. As well as calibration.However, neither on their own give “readings”. They need conditioning and interface circuitry. (I do recognise that the “inductance transducer” is a two-word item, and that the second word - transducer - implys that at least some form of signal conditioning exists therein.)That cicuitry is at least as important as the device itself.To give typical values for accuracy, is difficult without more specifics, though it is usual to be able to achieve several significant figures of accuracy out of each. 8. What is LVDT in measurement?A Linear Variable Differential Transducer is a sensor based on the idea of transformers. As its name shows it's a Linear sensor used in measuring displacements.  It has an iron core that moves up and down in the gap separating the primary and secondary coils. So the coils are not physically connected. The secondary coils are connected in opposition such that the output voltage is the difference between the voltages induced in the first and second secondary coils. The components whose Displacement is required to be measured should be connected to the core, so the input to the sensor is the displacement، the output would be the differential voltage output and after some manipulation using the sensitivity and sensor resolution, the displacement can be obtained. 9. How does a DC LVDT work?An oscillator/demodulator circuit built into the displacement transducer supplies the excitation and converts the return signal to a dc voltage. ... As the transducer contains internal signal conditioning electronics, there is no need for external signal conditioning. 10. Is LVDT an active transducer?The active transducer is also called a self-generating type transducer. ... Example of an active transducer is the bourdon tube. An example of a passive transducer is LVDT (linear variable differential transformer). It generates electric current or voltage directly in response to environmental stimulation.

The transformer is an essential part of electrical equipment. So it is necessary to know and master the basic knowledge of it. Is a necessary skill of every electric design. Catalog I. What is a Transformer? II. How does Transformer Works? III. What types of transformer are there? IV. What are the components of the transformer? V. What are the losses of transformers in operation? How to reduce them? VI. What is the nameplate of the transformer? What are the main technical   data on the nameplate? VII. How to choose a transformer? VIII.Why transformer cannot run when overload? IX. What kinds of tests should be done for transformers in operation? FAQ I. What is a Transformer? The transformer is a device that uses the principle of electromagnetic induction to change the AC voltage. The main components are primary coil, secondary coil, and core (magnetic core). The main functions are voltage conversion, current conversion, impedance transformation, isolation, voltage stabilization (magnetic saturation transformer), and so on. It can be divided into a power transformer and special transformer (furnace transformer, rectifier transformer, power frequency test transformer, voltage regulator, mine transformer, audio transformer, intermediate frequency transformer, high-frequency transformer, impulse transformer, instrument transformer, electronic transformers, reactors, voltage, and current transformer, etc.) The role of the core is to strengthen the magnetic coupling between the two coils. In order to reduce the eddy current and hysteresis loss in the iron, the iron core is formed by the superposition of the painted silicon steel sheet; there is no electrical connection between the two coils, and the coils are wound by insulated copper wire (or aluminum wire). One coil connected to the AC power supply is called the primary coil (or the primary coil) and the other coil is the secondary coil connected to electrical appliances. The actual transformers are very complicated, so there may be problems that exist to concern, such as copper loss (coil resistance heating), iron loss (core heating), magnetic flux leakage (air-closed magnetic induction line), and so on.  To simplify the discussion, an ideal transformer is introduced. An ideal transformer requires some necessary conditions: ignoring the flux leakage, ignoring the resistance of the primary and secondary coils, ignoring the loss of the iron core, and ignoring the no-load current (the current in the primary coil which supplies the secondary coil). For example, the power transformer is close to the ideal condition when it is running at full load (the output with a rated power of the secondary coil). The transformer is a static electrical appliance made by the principle of electromagnetic induction. When the primary coil of the transformer is connected to the AC power supply, the core produces an alternating flux, which is represented by φ. The φ in the primary and secondary coil is the same, and φ is also a simple harmonic function, and φ = φ msinωt. According to Faraday's law of electromagnetic induction, the induction electromotive force in the primary and secondary coils is e1=-N1d φ/dt, e2=-N2d φ /dt. N1, N2 is the number of turns of the secondary coil. From the diagram, we can see that U1=-e1, U2=e2(the primary coil physical quantity is represented by the subscript 1, the secondary coil physical quantity is indicated by the subscript 2), and the complex-effective value is U1=-E1=jN1 ω Φ, U2=E2=-jN2 ω Φ, and makes transformer ratio k=N 1 /N 2. From the upper formula, we can get U1 /U2=-N1 /N2=-k. that is, the voltage effective value of the transformer to that of two coils, which is equal to its coil-voltage ratio, and the phase difference of the voltage of two coils is π. Further More Based On Above Mentioned U1/U2=N1/N2 Under the condition that the no-load current can be neglected, there is I1 /I2=-N2 /N1, that is, the effective value of the coil's current is inversely proportional to the number of turns, and the phase difference is π. On the contrary, under the condition of no-load current, I1/ I2=N2/N1 The power of the ideal transformer is equal to that of the subsoils, that is P1=P2. It shows that the ideal transformer itself has no power loss. But there is always a loss in the actual transformer, and its efficiency is η= P2 /P1, for example, although power transformer efficiency is very high, can reach over 90%, still has a little loss. In an AC circuit, the equipment that increases or decreases the voltage is called a transformer. The transformer can transform any voltage into the value we need at the same frequency to meet the requirements of transmission and distribution. For example, the power generated by a power plant has a lower voltage level, which must be increased the voltage to transmit to a far distance, and the power area must reduce the voltage to a suitable voltage level for power equipment and daily use. II. How does Transformer Works? This video gives a detailed animated illustration on the working of electrical Transformers. Here the basic working principle and construction of transformer, step-up transformer, step-down transformer, transformer winding and core construction are well illustrated. Transformers are based on electromagnetic induction. It consists of an iron core made of silicon steel sheet (or silicon steel sheet) and two sets of coils around the core. The core and the coil are insulated from each other without any electrical connection. The coils connected to one side of the transformer and the power supply are called primary coils (or primary sides), and the coils that connect transformers and electrical equipment are called secondary coils (or secondary sides).  When the primary coil of the transformer is connected to the AC power supply, the changing magnetic field line in the core appears. Because the secondary coil is wound on the same iron core, the magnetic field line cuts the secondary coil, and the inductive electromotive force must be generated on the secondary coil, finally, the voltage at both ends of the coil generated. Because the magnetic line is alternating, the voltage of the secondary coil is also alternating. And its frequency is exactly the same as the frequency of the power supply. It is proved by the theory that the voltage ratio between the primary coil and the secondary coil is related to the turns of coils. It can be expressed as follows: Primary coil voltage / secondary coil voltage = primary coil turns / secondary coil turns, the higher the number of turns, the higher the voltage. Therefore, it can be seen that the turns of the secondary coil are less than the primary coils, that is, a step-down transformer, otherwise, it is a step-up transformer. III. What types of transformer are there? According to the number of phases, there are single-phase and three-phase transformers;  according to thefunction, there are power transformers, special power transformers, voltage regulating transformers, measuring transformers (voltage transformers, current transformers), small power transformers (for small power equipment), safety transformers;  according to the structure, there are core type and shell type; according to the coil, there has double winding and multi-winding transformers, auto-transformer; according to the cooling mode, oil-immersed type and air-cooled type transformers. IV. What are the components of the transformer? Transformer components are mainly composed of iron core, coil, also have other parts, such as oil tank, oil pillow, insulating sleeve and splice, etc. What’s the function of transformer oil? The functions of transformer oil are:  (1) insulation;   (2) heat dissipation;  (3) elimination of arc. What is autotransformer? The autotransformer has only one set of coils, and the secondary coils are tapped from the primary coils, and its electricity can transmitted. It not only has electromagnetic induction, but also the transmission of electricity. There are fewer silicon steel sheets and fewer copper wires in this kind of transformer than in ordinary transformers, often used to voltage regulator. How voltage regulator works? The voltage regulator is constructed the same as the autotransformer, but the iron core is made into a ring coil. The secondary coil tap uses a sliding brush contact to make the surface of the ring along the contact slip in a circular way to achieve voltage regulation smoothly. What is the current relationship between the primary coil and the secondary coil of the transformer? When the transformer operates with load, the current change of secondary coil will cause the corresponding change of primary coil current. According to the principle of magnetic potential balance, it is deduced that the current of the primary and secondary coil is inversely proportional to the number of turns of the coil, the current is small with more turns, and the current with less turns is large. The following formula can be expressed: primary coil current / secondary coil current = secondary coil turns / primary coil turns. What is the voltage change rate of a transformer? The voltage change rate of the voltage regulator is one of the main indexes of transformer performance. When the transformer supplies power to the load, the voltage at the load end of the transformer will inevitably decrease. Comparing the reduced voltage value with the rated voltage value, the percentage is the rate of voltage change. It can be expressed by the formula: voltage change rate = [(secondary rated voltage-load terminal voltage) / secondary rated voltage] ×100%. Generally, for the normal power transformer, when connected to the rated load, the voltage change rate is 4% to 6%. How to ensure that the transformer has a rated voltage output? Too high or too low voltage will affect the normal operation and service life of the transformer, so the voltage must be adjusted. The method of voltage regulation is to draw out several taps in the primary coil and connect them to the tap beginning, which changes the number of turns of the coil by turning the contact. In addition, the required rated voltage can be obtained by rotating the position of the tap switch. It also needs to note that voltage regulation usually occurs after the load of the transformer is cut off. What kind of small transformers are usually used? Where are they applied? Small transformers refer to single-phase transformers with a capacity below 1k VA, mostly used as power transformers for electrical equipment control, electronic equipment and safe lighting equipment. V. What are the losses of transformers in operation? How to reduce them? The loss of transformer in operation includes two parts. (1) One is caused by the iron core. When the coils are electrified, the magnetic field lines are alternating and cause eddy current and hysteresis loss in the core.  (2) Another loss is caused by the resistance of the coil itself. When the primary and secondary coils of the transformer have current passing through, some electrical energy may lose. The sum of iron loss and copper loss is the transformer loss, which is related to transformer capacity, voltage, and equipment utilization. Therefore, in the selection of transformers, the capacity of the equipment and the actual usage should be as consistent as possible, in order to improve the utilization rate of the equipment, pay attention not to make the transformer lies in light load operation. VI. What is the nameplate of the transformer?  The nameplate of the transformer should indicate the transformer's performance, technical specifications, and use occasions to meet the needs of the user. The main technical data usually selected are as follows: (1) The number of rated capacity. The output capacity of the transformer is rated. For example, the rated capacity of a single-phase transformer is Uline × I line, and the capacity of a three-phase transformer is also the U line × I line. (2) Rated voltage volts. Indicate the terminal voltage of the primary coil and the secondary coil (when the load is not attached). Note that the terminal voltage of the three-phase transformer refers to the line voltage U-line value. (3) Rated current amperes. It means LineI current value that allows long-term passage of primary and secondary coils at rated capacity and allowable temperature rise. (4) Voltage ratio. It is the ratio between primary coil rated voltage and secondary coil rated voltage. (5) Line connection mode. Single-phase transformers have only a set of coils of high and low voltage, only for single-phase use, and three-phase transformers have Y/△type. In addition to the above technical data, there are transformer rated frequency, phase number, temperature rise, impedance percentage of the transformer, etc. VII. How to choose a transformer?  First of all, it is necessary to investigate the power supply voltage of the place where the electricity is used, the actual power load of the user, and the conditions of the place where it is located, and then select one by one according to the technical data indicated by the nameplate of the transformer, generally from the capacity and voltage of the transformer. Considering the current and environmental conditions, the capacity selection should be based on the capacity, nature, and service time of the user's power equipment to determine the required load, and then select the transformer capacity. In normal operation, the power load of the transformer should be about 75% ~ 90% of the rated capacity of the transformer. When the actual load of the transformer is less than 50%, the small capacity transformer should be used, and the large transformer should be replaced immediately if the rated capacity of the transformer is greater than that of the transformer. At the same time, when selecting the transformer to determine the primary coil voltage of the transformer according to the line power supply and the voltage value of the secondary coil according to the electrical equipment, it is best to select the low-voltage three-phase four-wire power supply system. This can provide a power supply for the entire operation. For the selection of current, attention should be paid to that the load can meet the requirements of the motor when it starts (because the starting current of the motor is 4 ~ 7 times larger than that of the sinking operation). VIII. Why transformer cannot run when overload? Overload operation refers to the transformer operating in excess of the currency specified on the nameplate. Overload is divided into normal overload and accident overload. The former refers to the increase of power consumption under the normal power supply, and it often makes transformer temperature rise, impels transformer insulation to age, and reduces service life. Therefore, transformer overload is not allowed. In special cases, the overloading of transformers in a short period of time should not exceed 30% of the rated load in winter, and not more than 15% in summer. For the latter, the accident overload and allowable time requirements are as follows: Multiple of Rated LoadReasonable Time of Overload Multiple of Rated Load Reasonable Time of Overload Indoors Outdoors 1.30 2 hours 1 hour 1.60 30 minutes 15 minutes 1.75 15 minutes 8 minutes 2.00 7.5 minutes 4 minutes IX. What kinds of tests should be done for transformers in operation? In order to ensure the normal operation of the transformer, the following tests should be carried out regularly. (1) Temperature test. Whether the transformer is running normally, the temperature is very important. The regulations stipulate that the upper oil temperature shall not exceed 85℃(that is, the temperature rise is 55℃). General transformers are equipped with special temperature measuring devices. (2) Load measurement. In order to improve the utilization rate of transformers and reduce the loss of electric energy, it is necessary to determine the real power supply capacity of transformers in the operation of transformers, the measurement is usually carried out during the current peak period and is measured directly with a clamp ammeter. The current value shall be 70%~ 80% of the rated current of the transformer. (3) Voltage measurement. The regulation requires that the voltage range should be within ±5% of the rated voltage. If beyond this range, taps should be used to adjust the voltage to reach the specified range. Voltmeters are generally used to measure the terminal voltage of the secondary coil and the terminal voltage of the user. (4) Insulation resistance measurement. In order to keep the transformer in normal condition, insulation resistance must be measured to prevent insulation aging and accidents. When measuring the transformer, the transformer should stop running and the insulation resistance of the transformer should be measured by using the tramegger. The resistance measured should not be less than 70 percent of the previously measured value. When using tramegger, the low-voltage coil may adopt a voltage grade of 500 volts. FAQ 1. What is the use of transformer? Transformers are employed for widely varying purposes; e.g., to reduce the voltage of conventional power circuits to operate low-voltage devices, such as doorbells and toy electric trains, and to raise the voltage from electric generators so that electric power can be transmitted over long distances. 2. What are the 3 types of transformers? There are three primary types of voltage transformers (VT): electromagnetic, capacitor, and optical. 3. What is the basic principle of transformer? A transformer consists of two electrically isolated coils and operates on Faraday's principal of “mutual induction”, in which an EMF is induced in the transformers secondary coil by the magnetic flux generated by the voltages and currents flowing in the primary coil winding. 4. Does a transformer convert AC to DC? A transformer is built to transfer the energy from one circuit into another circuit by way of magnetic coupling. ... An alternating current creates a magnetic flux in the core on its way through the first winding, inducing the voltage in the others. It can convert high and low voltages, it cannot convert AC to DC. 5. What are the main parts of transformer? There are three basic parts of a transformer: a. an iron core which serves as a magnetic conductor, b. a primary winding or coil of wire and. c. a secondary winding or coil of wire. 6. What are the classification of transformer? Depending upon the type of construction used, the transformers are classified into two categories viz.: (i) Core type, and (ii) Shell type. Depending upon the type of service, in the field of power system, they are classified as: (i) Power transformers, and (ii) Distribution transformers. 7. Can a transformer work on DC? As mentioned before, transformers do not allow DC input to flow through. This is known as DC isolation. This is because a change in current cannot be generated by DC; meaning that there is no changing magnetic field to induce a voltage across the secondary component. 8. How do you convert a transformer? This conversion is made by winding two separate conductors around a common iron core. Applying an alternating voltage to the primary conductor produces current which sets up a magnetic field around itself. This is known as mutual inductance. 9. What are two components of no load current in transformer? The no-load current of a transformer consists of two components: The Magnetization Current iM is the current required to produce the flux in the transformer core. The Core-loss Current ih+e is the current required to make up for hysteresis and eddy current losses. 10. Which type of transformer core is most efficient? SHELL CORE. The most popular and efficient transformer core is the SHELL CORE, as illustrated in figure (4). As shown, each layer of the core consists of E- and I-shaped sections of metal. These sections are butted together to form the laminations. 11. What is the power factor of transformer? The power factor of a distribution transformer is between (0.75 to 0.80) when secondary is connected to u.p.f loads. 12. Why do we need Transformers? Transformers help improve safety and efficiency of power systems by raising and lowering voltage levels as and when needed. They are used in a wide range of residential and industrial applications, primarily and perhaps most importantly in the distribution and regulation of power across long distances. 13. What is the difference between a step up transformer and a step down transformer? A transformer that increases the voltage from primary to secondary (more secondary winding turns than primary winding turns) is called a step-up transformer. Conversely, a transformer designed to do just the opposite is called a step-down transformer. 14. Are transformers dangerous? There is no established evidence that the exposure to magnetic fields from powerlines, substations, transformers or other electrical sources, regardless of the proximity, causes any health effects. 15. Why transformer rating is in kVA not in kW? Copper losses (I²R) depends on current which passing through transformer winding while Iron losses or core losses or Insulation losses depends on Voltage. ... That's why the transformer rating may be expressed in VA or kVA, not in W or kW.

Warm hints: The word in this article is about 3000 words and  reading time is about 10 minutes.   The transformer is a static electrical device, mainly composed of an iron core (or magnetic core) and coil. The coils have two or more windings, of which the ones connected to the power are called primary coils, and the rest are called secondary coils. Transformers are widely used in electrical equipment such as household appliances, electronic equipment, switching power supply, and so on. Circuit symbols commonly used T as the beginning of the number, for example, T01, T201.    This article covers the construction, functions, classification, and design of transformers and materials used for building magnetic cores in transformers.     Catalogs   I. The Composition of Transformer II. The Construction and Functions of Transformer III. High-frequency Transformer Design Program 3.1 Program structure 3.2 Matters needing attention when doing the core material   selection 3.3 Ferrite magnetic material requirements IV. Power Transformer Classification V. Principle and method of Transformer Design FAQ   I. The Composition of Transformer 1）The primary side 2）The secondary side 3）Magnetizing inductance 4）Leakage inductance 5）Open-circuit or short-circuit measurement of the primary side leads to the  Magnetic inductance and the leakage inductance turns ratio respectively:  K=Np/Ns=V1/V2   II. The Construction and Functions of Transformer 1) Electrical isolation 2) Energy storage 3) Voltage change for same power input.   III. High-frequency Transformer Design Program   3.1 Program structure (1) Core material (2) Core structure (3) Core parameters (4) Transformer Winding Parameter (5) package assembly (6) Temperature rise check   (1) Core material Soft magnetic ferrite is widely used in switching power supply because of its own characteristics. It has the advantages of high resistivity, low AC eddy current losses, low price, and easy to be machined into magnetic cores of various shapes. The disadvantages are low working magnetic flux density, low permeability, large magnetostriction, and high sensitivity to temperature changes. Which kind of soft magnetic ferrite material can satisfy the design requirement of a high-frequency transformer more fully, only when it is carefully considered and the transformer design can reach the high-cost performance.   (2) Magnetic core structure The factors considered in the selection of magnetic core structure are as follows: reducing magnetic leakage and leakage inductance, increasing the area of coil heat dissipation, which is beneficial for shielding and makes it easier to wind coils, more convenient to wire for assembly and so on.   The magnetic leakage and leakage inductance are directly related to the magnetic core structure . If the magnetic core does not need air gap, then a enclosed ring-like or square type magnetic core may be used as far as possible.   (3) Magnetic core parameters In the design of core parameters, special attention should be paid to the operating flux density only limited by the magnetization curve, but also by the losses, and also related to the working mode of power transmission. When the flux changes in one direction, there is ΔB=Bs-Br, which is not only limited by the saturation flux density but also mainly by the losses (Losses cause temperature rise, which in turn affects magnetic flux density). The operating flux density Bm=0.6～0.7ΔB.   An air gap can decrease Br and therefore increase the flux density ΔB. The exciting current can be increased after using an air gap opening, but the core volume can be decreased either. For the two-way operation of magnetic flux, the flux density ΔB is twice the maximum operating flux density Bm, that is ΔB=2Bm. In bidirectional operating mode, we should pay attention to the problem of transformer DC magnetic bias due to the inequality of volt-second areas of positive and negative excitation variation, which is caused by different reasons. A small air gap will be needed in the core, or a DC capacitor can also be added to the circuit design.   Magnetic properties of ferromagnetic materials Magnetic hysteresis loops of the core   (4) Coil parameters Coil parameters include: turns, conductor section (diameter), wire form, winding arrangement and insulation. The conductor section (diameter) depends on the current density of winding, using taking 2.5～4A/mm2. When doing some choosing of section conductor diameter don’t forget to take the skin effect into consideration and do regulations necessary after some temperature rise tests of the transformer.   General winding arrangements: the primary winding is close to the core and the secondary windings & feedback windings are gradually arranged outward. The following two winding arrangements are recommended:   1) If the voltage of the original windings is high (for example, 220V) and meanwhile that of the secondary windings is low, a more appropriate arrangement is the secondary winding being close to the core, and then goes the feedback winding, the original winding is arranged on the outermost ends, which is advantageous to the insulation arrangement of the original winding to the core;   2) If we want to increase the coupling between the primary and secondary windings, we can make half of the original windings be close to the core, then goes the feedback winding and secondary winding, and the other half of the original winding being the outermost ends, which is an arrangement advantageous to reduce the leakage inductance.   (5) Assembly structure The assembly structure of high-frequency power transformers are divided into horizontal and vertical types. If you'd like to select the planar core, sheet magnetic core and thin-film magnetic core, then a horizontal-type assembly would do you good.   (6) Temperature rise tests The temperature rise tests can be carried out by calculation and sample test. The temperature rise is lower than the allowable temperature rise above 15 degrees, the current density and the cross-section of the wire are appropriately increased. Appropriately increase the current density and decrease the cross-section of the wire, and do the exact opposite if temperature rise exceeds the allowable value, such as increasing the diameter or enlarging the core if necessary, to increase the area of coil heat dissipation.       3.2 Matters needing attention when doing the core material selection (1) Soft ferrite, due to its low price, good adaptability, and high performance at high frequency, has been widely used in switching power supply.   (2) Soft ferrite is commonly divided into two series: Mn-Zn ferrite and Ni-Zn ferrite. The Mn-Zn ferrite is composed of Fe2O3，MnCO3，ZnO and so on, which is widely used in all kinds of filters, inductors, transformers, and so on below 1MHz. The Ni-Zn ferrite is composed of Fe2O3，NiO，ZnO and so on, which is widely used in all kinds of adjustable inductor windings, anti-jamming magnetic beads, antenna matching devices, and so on above 1MHz.    (3) Mn-Zn ferrite is the most widely used core in switching power supply, and the selection of its material depends on its use. The core for the input filter part of the power supply is mostly high-conductivity magnetic core, and its material number mostly is R4K～R10K, that is, the ferrite core of relative permeability is about 4000~10000, but the main transformer and output filter are magnetic materials with high saturation flux density, where Bs is about 0.5T (5000GS).     3.3 Ferrite magnetic material requirements   Ferrite magnetic materials for switching power supply shall meet the following requirements:   (1) High saturation flux density Bs and low residual flux density Br   The residual flux density Bs has a certain influence on the transformer and winding results. Theoretically speaking, the number of turns of transformer windings can be reduced and the copper loss can be reduced because of the high Bs. In practical applications, there are different types of circuits of high-frequency converters in switching power supply.    For transformers, their operations can be divided into two categories:   1) Bipolar: The circuit topologies include half-bridge, full-bridge, push-pull, etc. In the primary winding of the transformer, the excitation current is equal and opposite in direction during the positive and negative half-cycles. Therefore, the magnetic flux changes in the magnetic core of the transformer are symmetrically moved up and down. The maximum variation range of B is  ΔB=2Bm, and the DC component of the magnetic core is basically canceling out.   2) Unipolar: The circuit topologies include single-ended forward, single-ended flyback, etc. The transformer primary winding adds a unidirectional square wave pulse voltage in one cycle (this is the case for single-ended flyback). The magnetic flux density varies from the maximum Bm to the residual flux density Br in the unidirectional-excitation transformer core. If we decrease the Br and increase the saturation flux density Bs, then the △B will be increased, and the turns and copper loss will also be reduced.   (2) Transformers or inductors are divided into three categories according to their topology:   1) An DC-filter inductor's magnetic core only works in one quadrant, the topologies of this operating state including Boost, Buck, buck/boost inductors, single end flyback converter transformer, forward and all push-pull converters and output filter inductors.   2) The core of the transformer in the forward converter also works in one quadrant, but the transformer needs to magnetic reset.   3) The core of the transformer with push-pull topology is in bidirectional alternating magnetization. These kinds of converters include push-pull, half-bridge and full-bridge converters, AC filter inductors, and so on.   (3) Low power loss at high frequency   The power loss of ferrite not only affects the power output efficiency but also leads to the heating of the magnetic core and waveform distortion.   The heating problem of the transformer is very common in practical applications, which is mainly caused by copper loss and core loss of the transformer. If the selected Bm is too low and the turns of winding are too many, it will cause the winding to heat up and transfer the heat to the core at the same time, and vice versa.   When selecting the ferrite material, we must make the power loss change with temperature characterized by a negative temperature coefficient. This is because if the core loss is the main heating, making the transformer temperature rise up, which then will lead to a further increase of core losses, thus it will form a vicious circle and eventually make the power tube, transformer, and other components burn down. Therefore, in the researches of power ferrite at home and abroad, we must solve the problem of negative temperature coefficient of magnetic material power loss itself, which is also a remarkable feature of magnetic materials having met the requirements for power supply applications, such as PC40 from Japanese company TDK and R2KB from China manufacturers and so on.   (4) A relatively moderate permeability   (5) How we choose the appropriate relative permeability?    Well, this depends on the switching frequency of your actual circuit, mostly 2000, meanwhile its applicable frequency must be below 300kHz, and sometimes can be a little higher, but the maximum will not be higher than 500 kHz.   (6) A relatively high Curie temperature   Curie temperature is the temperature at which a magnetic material loses its magnetic properties, generally above 200 ℃. However, the actual operating temperature of the transformer should not be higher than 80℃, at which the saturation flux density Bs will drop to 70% of that at the normal temperature when the temperature is above 100℃. That is, the saturation flux density of the core will drop more seriously when the operating temperature is too high. Furthermore, when the temperature is higher than 100℃, the power loss has been experiencing a positive temperature coefficient, which will lead to a vicious circle. For R2KB2 materials, the temperature corresponding to the allowable power consumption has reached 110℃ and the Curie temperature is up to 240℃, which meets the requirements of high-temperature use.     IV. Power Transformer Classification Power transformers are divided into three categories according to their topology: (1) Flyback transformers; (2) Forward transformers; (3) Push-pull transformers (full-bridge/half-bridge converters)   The appropriate topologies for various core structures are shown in the following table:   Core structureTypes of converter circuitFlybackForwardPush-pullE cores++0Planar E Cores-+0EFD Cores-++ETD Cores0++ER Cores0++U Cores+00RM Cores0+0EP Cores-+0P Cores-+0Ring Cores-++    "+"=fit; "0"=normal; "-"=unfit Summary of High frequency transformer core.XLS V. Principle and Method of Transformer Design   (1) There are two main ways to design transformer: Area Product (AP) Method AP: The product of core effective cross section Ae and Area of window Aw PT-The calculation power of the transformer Ae-Core effective cross section Aw- Area of window Ko-Core window utilization coefficient, typically 0.4 Kf-Waveform coefficient, usually square wave being 4 and sine wave being 4.44 Bw-The operating magnetic intensity of core FS-Switching frequency Kj-Current density coefficient, usually 395A/cm2 X-Core structure coefficient     (2) According to the area product (AP) method, the general steps of designing transformer are as follows: 1. Select the core material to calculate the apparent power of the transformer; 2. Determine the core cross section AP and select the core size according to AP value; 3. Calculation of the primary side inductance and the number of turns; 4. Calculation of the length of air gap; 5. Calculating the line diameter according to the current density and the secondary side RMS current. 6. Determine whether the copper loss and iron loss meet the requirements (eg allowable loss and temperature rise)   Selecting the flyback topology, the basic parameters of the power supply are as follows: Input voltage: 175-264 VAC Output voltage: 21V Output current: 3A Output power P0=63W Frequency set at 60Khz Duty cycle set at 0.45 initially   1) Select the core material to determine the apparent power PT of the transformer   and select the PC40 material here considering the cost factor and check the PC40 data to get Bs=0.39T, Br=0.06T. In order to prevent the core from becoming saturated instantly, a certain margin is reserved. Let Bm= ΔBmax*0.6=0.198T, and pick up the 0.2T. For flyback topology, the transformer apparent power PT is:   2) Calculating AP values with Excel tables   Where, J is the current density, usually 395A/cm2, and Ku is the effective use coefficient of copper window, usually 0.2～0.4, now we set Ku as 0.4.    Based on the figure above, we select the core EE3528 due to its being greater than the calculated AP value, with the following parameters: Ae: 84.8mm2 AP：1.3398cm4 Wa：158mm2 AL：2600nH/H2 In order to adapt to the abrupt load current, the power supply is designed in critical mode and the critical current is: I0B=0.8×I0=2.4A     3) Calculation of the primary side inductance and the number of turns (A) Minimum input voltage Vimin=ViACmin*1.2=210V (B) Turns ratio n=[Vimin/(V0+Vf)]*[Dmax/(1-Dmax)] n=[210V/(21V+1V)*[0.45/(1-0.45)] n=7.8 (C) Peak secondary current ^IsB=2*IoB/(1-Dmax) ^IsB=2*2.4A/(1-0.45) ^IsB=8.72A (D) Secondary inductance Ls=(V0+Vf)*(1-Dmax)*[1/(Fs*1000)]/^IsB*1000000 Ls=(21V+1V)*(1-0.45)*[1/(60Khz*1000)]/8.72A*1000000 Ls=23.58Uh (E) Primary inductance Lp=n*n*Ls Lp=7.8*7.8*23.58uH Lp=1434uH   Primary and secondary peak currents (F) Calculation of peak secondary current in continuous mode ^Isp=Io/(1-Dmax)+(^IsB/2) ^Isp=3A/(1-0.45)+(8.72A/2) ^Isp=9.81A (G) Calculation of peak primary current in continuous mode ^Ipp=^Isp/n ^Ipp=9.8A/7.8 ^Ipp=1.257A (H) Calculating the turns of the primary and secondary auxiliary windings a) Number of turns in the primary side Np=Lp*^Ipp/(^B*Ae) Np=1434uH*1.257A/(0.2*84.8) Np=106.28T After rounding: Np=106T b) Number of turns in the secondary side Ns=Np/n Ns=106T/7.8 Ns=13.58T After rounding: Ns=14T c) Number of feedback turns Nv=(Vcc+Vf)/[(V0+Vf)/Ns] Nv=(14.5V+1V)/[(21V+1V)/14T] Nv=9.87T After rounding: Nv=10T   To avoid core saturation, an appropriate air gap is added to the magnetic loop, the calculation go as follows: The number of turns may need to be corrected by the air-gap flux edge effect.   4) There are two ways to calculate the wire diameters of the primary, secondary and auxiliary windings: Effective current of original side diameter: Iprms=Po/^n/Vimin Iprms=63W/0.8/210V Iprms=0.375A (A) Calculating the area of bare wire (B) Calculating the wire diameter (current density J to take 4A/mm2) Using two 0.18mm-diameter wires wound around or AWG #28 a single strand The secondary diameter: Use four wires with a diameter of 0.25mm (AWG #31) and wind around. Calculation of Skin Depth: The diameter of multi-strand parallel winding must be less than or equal to dwH, in single wire winding, however, if the diameter exceeds the dWH value,  the multi-strand wire winding should be taken into account.   5) Calculation of copper loss Pcu and iron loss Pfe (total transformer loss Ploss) (A) Calculating the loss of primary and secondary windings.  Where, MLT is the average turn length of magnetic core (B) Calculating the allowable total loss Ploss and allowable iron loss at efficiency η (C) According to the loss curve of iron core, the actual loss (iron loss per unit weight and actual iron loss) is obtained by: The Ploss is the loss of the whole circuit, including diode/MOSFET losses and other losses, the actual losses Pfe must be much smaller than the calculated one, so here is only for reference. (D) Calculating the loss per unit area by Φ=Ploss/As If the temperature rise caused by Φ is less than 25 degrees, then the design is wonderful.   6) Calculating the BW The working flux density BW should be below Bs-Br within the design specifications, that is Bw<Bs-Br, to avoid saturation of the core.   FAQ   1. What is the use of transformer? Transformers are employed for widely varying purposes; e.g., to reduce the voltage of conventional power circuits to operate low-voltage devices, such as doorbells and toy electric trains, and to raise the voltage from electric generators so that electric power can be transmitted over long distances.   2. What are the 3 types of transformers? There are three primary types of voltage transformers (VT): electromagnetic, capacitor, and optical.   3. What is the basic principle of transformer? A transformer consists of two electrically isolated coils and operates on Faraday's principal of “mutual induction”, in which an EMF is induced in the transformers secondary coil by the magnetic flux generated by the voltages and currents flowing in the primary coil winding.   4. Does a transformer convert AC to DC? A transformer is built to transfer the energy from one circuit into another circuit by way of magnetic coupling. ... An alternating current creates a magnetic flux in the core on its way through the first winding, inducing the voltage in the others. It can convert high and low voltages, it cannot convert AC to DC.   5. What are the main parts of transformer? There are three basic parts of a transformer: a. an iron core which serves as a magnetic conductor, b. a primary winding or coil of wire and. c. a secondary winding or coil of wire.   6. What are the classification of transformer? Depending upon the type of construction used, the transformers are classified into two categories viz.: (i) Core type, and (ii) Shell type. Depending upon the type of service, in the field of power system, they are classified as: (i) Power transformers, and (ii) Distribution transformers.   7. Can a transformer work on DC? As mentioned before, transformers do not allow DC input to flow through. This is known as DC isolation. This is because a change in current cannot be generated by DC; meaning that there is no changing magnetic field to induce a voltage across the secondary component.   8. How do you convert a transformer? This conversion is made by winding two separate conductors around a common iron core. Applying an alternating voltage to the primary conductor produces current which sets up a magnetic field around itself. This is known as mutual inductance.   9. What are two components of no load current in transformer? The no-load current of a transformer consists of two components: The Magnetization Current iM is the current required to produce the flux in the transformer core. The Core-loss Current ih+e is the current required to make up for hysteresis and eddy current losses.   10. Which type of transformer core is most efficient? SHELL CORE. The most popular and efficient transformer core is the SHELL CORE, as illustrated in figure (4). As shown, each layer of the core consists of E- and I-shaped sections of metal. These sections are butted together to form the laminations.   You May Also Like: Analysis of Calculation Theory for Transformer Temperature Rise Some suggestions about protecting transformers Learn Some Basic Knowledge about Capacitor Voltage Transformer