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Warm hints: The word in this article is about 3000 words and  reading time is about 15 minutes.   This paper is mainly about how to learn analog circuit design. An analog circuit is a circuit used to transmit, transform, process, amplify, measure, and display analog signals. Analog signals refer to continuously changing electrical signals. Analog circuit is the basis of the electronic circuit, which mainly includes amplifier circuit, signal processing, and processing circuit, oscillation circuit, modulation and demodulation circuit, and power supply.    Analog circuit   Catalogs   I. What’s the Engineering Thinking in Analog Circuit II. Commonly Used Semiconductor Devices III. Negative Feedback Basic Concepts IV. Operational Amplifier Development V. Conclusion FAQ I. What’s the Engineering Thinking in Analog Circuit   Analog circuit is a very important profession, and difficult for people to learn. Now, let me talk about my understanding of the analog circuit. When it comes to the understanding and application of analog circuits, I’ve done some projects and participated in competitions. The analog circuit is an engineering course, and the earning focus is to master the engineering ideas. It’s better to put it into practice, instead of only doing the exams. What is the engineering idea? Encyclopedia +explains as this: "Engineering is the application of science and mathematics. Through this, natural material and energy characteristics can be made into efficient, reliable, and human-friendly products flow through a variety of structures, machines, products, systems, and processes, with the shortest Time, and less refined manpower, so the concept of engineering comes out and it has evolved into an independent discipline and skill. "For example, in analog circuits, there is a very Important engineering thinking - approximation.   In high school physics class, we learn a lot of circuits are ideal circuits. The wire resistance is always 0, the transformer efficiency is 100%, the ideal voltmeter resistance is infinite, the ideal ammeter resistance is 0, and so on. You can see that many times the calculation in an analog circuit will often omit one or two smaller items and use the equal sign instead of the equal sign directly.   Why use an approximation? To put it plainly, people’s understanding of nature in human science is not comprehensive enough to describe the natural phenomenon with absolute precision. Or human’s understanding is limited. By the means of approximation, people have not only achieved an obvious effect on solving the problem but also greatly simplifies the procedure and saves time and effort. With this thought, many achievements have been made in human science, which has also proved its reliability.    Summary Mold itself is a very complex subject, and the molding course is just one of the most basic things. Analog Circuit Meaning is the electronic circuit that processes analog signals. Most of the signals in nature are analog signals, and they have continuous amplitude values, such as the sound signal when speaking. Analog circuits can be such signal processing (of course, need to be converted into electrical signals), such as amplifier to amplify the sound signal, the radio can send analog sound signals, image signals. It can even be assumed that all circuits are based on analog circuits (even for digital circuits, the underlying principle is based on analog circuits). Its importance is self-evident.    Due to the rapid development of digital circuits and programmable devices, many superior features are demonstrated. Many electronic devices are slowly digital but still can not do without analog circuits. The most important analog circuit devices, non-semiconductor devices are none other than. The most basic and commonly used semiconductor devices are diodes, transistors, FETs, and operational amplifiers. II. Commonly Used Semiconductor Devices   The diodes have many roles. Ordinary diodes can be used for rectification, light-emitting diodes can be used for indicator and lighting, regulators can be regulated, varactor diodes can be used for signal modulation. The mold course related to the part of the diode is relatively simple. And many characteristics of the FET are similar to the transistor, so we often explain transistor or amplifier instead.    The basic function of the transistor is to enlarge. The transistor constitutes a variety of circuits because of its features, reflecting a lot of engineering ideas. The transistor-based circuit is the amplifier whose input sound is small, the output sound is great. Amplifier output and the input voltage (or current) ratio is called magnification, also known as gain. For a voltage, if the time for the horizontal axis, voltage vertical axis for mapping, the graph is the voltage waveform. If an amplifier with a gain of 5 inputs a constant voltage of 1V (the waveform on the left is shown below), the output should always be 5V (the waveform is shown in the middle figure below), neither changing with time nor changing with temperature And the input voltage exactly the same shape. However, if the magnification is unstable and constantly changing, the original input signal will be distorted (as shown on the right), and the signal may change from a horizontal straight line to a curved line. This waveform change is called distortion. Voltage waveform   III. Negative Feedback Basic Concepts   The basic concept of negative feedback makes some very powerful people find a good way: negative feedback. What is negative feedback? "Feedback refers to the output of the system is returned to the input and affect the input, thus affecting the overall system output Feedback can be divided into positive feedback and negative feedback is to make the output and input the opposite effect, the system Output tends to be stable. "The above explanation is hard to make sense. I have two examples. When playing the inverted pendulum, we propped up an inverted wooden stick by hand. When the wooden stick was tilted in one direction, we offset the change by moving the hand to the direction of the stick so that the stick could be in our hand's balance.    When I was in high school, I often had a monthly test. I found that some of my classmates had a habit of starting a good study when a test score was poor and going up next time. When the test was better, the next month will be relaxed, so results will come down again, so again and again. Both of these examples illustrate that negative feedback can make the system more stable. We ignore the specific circuit, only draw a simple diagram to illustrate how the transistor amplifier uses the negative feedback. The triangle below shows a transistor consisting of an amplifier, the magnification is A, the input is I, the output O = I * A, because the magnification A instability, so the output waveform will be distorted.  Negative feedback   Some devices have been added to the circuit as follows. The purple circle is the adder, combined with the purple "+", "-" symbol that its output Y = (+ I) + (- X) = I-X, in the actual circuit with the resistance can be achieved; Block F is the feedback device, which means that the signal is taken out from the output O and multiplied by F to get X, so X = O * F, where F <1 (this part can be realized by resistance in the actual circuit). Triangle refers to the amplifier A, mainly composed of transistors, meeting O = A * Y, and A magnification is unstable, easy to be disturbed. Add a feedback device   You can list the equations: Y = I-XO = Y * AX = O * F to calculate the gain of the entire circuit: Formula   If the magnification A is very large, while F is not small, A * F 》》1 symbol "》》" suggests far greater than the approximate idea. The entire circuit magnification: Formula   IV. Operational Amplifier Development   1.Working principle of operational amplifier Because the feedback device can be realized by the resistance, the resistance value of the ordinary resistance is not easily disturbed by the outside world, so the value of F is very steady, so the magnification of the whole circuit is very steady. We succeeded in solving the stability problem of the transistor by negative feedback. We can see here that the feedback part and the amplification part form a ring, so the amplification of the whole circuit is called the loop gain or the closed-loop gain. Before adding the feedback, the amplification of circuit A is called the open-loop gain. Due to the negative feedback, the stability of the circuit is improved, but there is also a cost: Because the AF 》》1, then "A》》1 / F" open-loop gain is much larger than the closed-loop gain, which means the amplifier gain is greatly reduced. But in general, this is worth it for stability. Operational amplifier In the above circuit, in order to actually create a large open-loop amplifier gain A, often with multi-stage transistor amplifier in series design.   Because the high demand for such high-gain amplifiers is very common, so some people in history put them into a finished circuit board module. This is used directly as a component on the line when needed because it’s very convenient. This is the original op-amp, which is referred to as op-amp. The development of integrated circuits makes a large number of transistor components integrated into a small chip possible, so the common integrated operational amplifier turns up today.    The "op-amp" is named for its mathematical operation originally used to simulate computers. Although now widely used digital computer is no longer used to calculate the operational amplifier, but the name still retained. Today, op-amps play an important role in analog circuits and have also become one of the focuses of the analog circuit. The op-amp has virtual short and virtual interrupt characteristics. Usually, op-amp has two inputs U + and U-, an output Uo, between them to meet Uo = A * (U + -U-) op-amp open-loop gain A often up to dozens Million ~ millions, but the op-amp output voltage limited by the supply voltage can not exceed the supply voltage. So the op-amp input-output relationship similar to the shape below. In the figure, the horizontal axis is (U + -U-) and the vertical axis is Uo. Op amp input - output In the middle of a straight line, the op-amp is in the normal state of amplification, called the linear region, meeting Uo = A * (U + -U-). When the absolute value of the input becomes slightly larger, the output will be power limited, no longer satisfying the above relationship. The value of Uo is usually slightly smaller than the supply voltage range (note that the op-amp can be dual supply, that is the supply voltage range can be afloat between a negative value and a positive value), which is called the non-linear region. Rail-to-rail op-amp output can reach the power supply voltage.   When the operational amplifier in the linear region, the Uo value is very limited, but A large. So U + -U- = UoA ≈ 0 or U + ≈ U-. At this time, the positive and negative op-amp input voltage is almost equal, like a short circuit similarly, which is called a short circuit. So only when the operational amplifier in the enlarged area will have "virtual short" characteristics, rather than the inherent properties of the op-amp. On the other hand, due to the internal structure of the op-amp, its input impedance is large.    The input impedance can be simply understood as: the input impedance = input voltage/input current input impedance, which means that the op-amp input with only a small current can work properly. Because of this, an op-amp can be used for some weak current detection, such as the human brain, myoelectric wave, whose maximum voltage is only a few mV, the current value is very small. This feature of the op-amp is called a virtual interrupt, meaning that there is almost no current flowing into the input like the open circuit. Different from the short circuit, a virtual interrupt is the inherent properties of the op-amp, which will not change with the circuit.   2.Op amp non-ideal characteristics   The op amp's non-ideal characteristics of the op-amp by the transistor composition. Obviously, like the transistor, there will be many undesirable characteristics. The actual operational amplifier will not fully meet the short virtual fault characteristics. Its normal work needs input current input, which is called the input bias current.    The same op-amp input offset voltage, input offset voltage, input offset current, and other non-ideal parameters. These non-ideal characteristics, such as the input bias current is small, sometimes will have a great impact on the circuit, resulting in the circuit does not work. Therefore, there are some ways to reduce the impact of these factors. In practical applications, the non-ideal characteristics of the op-amp are a very important issue. There are many ways to eliminate the non-ideal characteristics of the op-amp, but not introduced here.    Other cores of the molding course are the transistor and op-amp. Around these devices, the molding course will explain a variety of circuits, including the calculation of the amplifier circuit analysis, multi-stage amplifier circuit, the amplifier frequency characteristics, the idea of feedback, power amplifier circuit, comparator, oscillator, integrator, differentiator, waveform generation, Signal processing, filter, integrated power supply circuit and so on. When comparing op-amp and transistor In the actual design of the circuit, the op-amp will be more than the transistor. Because many of the features of op-amps are better than triodes, the circuit design is simple, and the cost of op-amps is often not too high.   Many times you can achieve the same effect with the transistor and op-amp and lower cost of each op-amp. Because op-amps integrate a large number of transistors, the average cost per transistor is very low. For example, a conventional audio pre-amplifier can be handled with a universal op-amp. and if you use the transistor, you may need more transistors, and the human cost during design is far higher than the op-amp program. Of course, the transistor has its advantages.    In some very simple circuits, the stability of the magnification is not strictly required, one or two transistors can accomplish. And triodes are often used to save costs. In addition, in some extreme conditions, such as working in high-frequency and high-power environments (such as RF signal transmitting circuits), a well-designed triode circuit will perform much better than an op-amp, or at a much lower cost. Even in some conditions, only the transistors can be completed, then you need to choose the transistor to build the circuit.   This video give a detailed explanation about analog circuit: Analog Circuits Lecture V. Conclusion   Analog circuits are a very complex discipline that involves more than knowledge written in books. Books are generally introduced in accordance with the principle of work, simplifying a lot of difficulties to understand, but in reality, more factors must be considered. So the gap between the actual circuit and the book is very large. Such as triangular wave generator built with an op-amp introduced in analog circuit books usually can not work in all likelihood. However, the main principle of the actual circuit is the same as the book description. Therefore, the design of analog circuits often requires a lot of experience, for there are many things that can not be explained and even difficult to calculate. I hope this article can help you learn more about analog circuits. FAQ   1. What is meant by analog circuit? The Analog electronic circuit includes an analog signal with any continuously changeable signal. While working on an analog signal, an analog circuit alters the signal in some manner. Analog circuit can be used to convert the original signal into some other format such as a digital signal.   2. What is the difference between digital and analog circuits? Analog Circuits and Digital Circuits is a classic way of differentiating between two types of electronic circuits based on the signals they process. To put it in simple words, Analog Circuits deals with continuous analog signals whereas Digital Circuits deals with discrete digital signals.   3. Where are analog circuits used? Analog circuits represent key components of communications and other systems in widespread, growing commercial use. High-speed transistors are essential to the operation of such circuits.   4. Is digital cheaper than analog? If you are looking at the straight-up module cost an analog vs. a digital version, then yes, the analog module will likely be a cheaper solution. However, if you look at the total cost, or the “value” of the digital module versus an analog solution, then digital will in fact be “cheaper”.   5. What is analog design? Analog design is part of integrated circuit design and focuses on signal fidelity, amplification and filtering. Those who perform the function of analog design are qualified electrical engineers.   6. Why is analog design difficult? Ask most engineers and they would tell you why: analog design is harder than digital, and requires more knowledge and more factors to consider such as a deep understanding of efficient power, precision measurement, wireless connectivity, and reliable circuit protection.   7. Which is better analog or digital design? Analog circuits can be precise, elegant design with various components with very simple. For example, two resistors joining to make a voltage divider. Generally, Analog circuits are much more complex to design compared to which complete the same task as digitally.   8. What is the tool used for analog circuit design? A suite of web tools to help you design signal conditioning circuits faster: Analog Filter Wizard, Precision ADC Driver Tool, Photodiode Wizard, In Amp Diamond Plot, Direct Digital Synthesis Simulator, and Virtual Eval.   9. How hard is circuit design? Circuit design is a lot like any other learned skill, you start with the basics. These basic circuits can be learned in a few days. ... So yes, it can be very difficult to reach a high level of design expertise and you never really master it because the art continues to evolve.   10. How does circuit design work? Digital electronic circuit design takes the electrical signals in the form of discrete values. The data are represented in the form of zeros and ones. Digital circuits extensively use transistors, interconnected to give create logic gates that provide the function of Boolean logic.   You May Also Like:   Look Forward to the Future of Semiconductor GaN High-Electron Mobility Transistor Power Amplifier Trojans are everywhere even the hardware Remote Electronic Transport Promote Organic Photovaltaic Power Generation Make Next-Gen of Computer Be Faster,Better, More efficient Some suggestions about protecting transformers  

SummaryResearchers at TU Wien have succeeded in developing a method for the controlled manufacture of porous silicon carbide. Silicon carbide has significant advantages over silicon; it has greater chemical resistance and can therefore be used for biological applications, for example, without any additional coating required.Extremely fine porous structures with tiny holes – resembling a kind of sponge at nano level – can be generated in semiconductors. This opens up new possibilities for the realization of tiny sensors or unusual optical and electronic components. There have already been experiments in this area with porous structures made from silicon.To demonstrate the potential of this new technology, a special mirror that selectively reflects different colors of light has been integrated into a SiC wafer by creating thin layers with a thickness of approximately 70nm each and with different degrees of porosity. “There is a whole range of exciting technical possibilities available to us when making a porous structure with countless nano holes from a solid piece of a semiconductor material,” says Markus Leitgeb from the Institute of Sensor and Actuator Systems at TU Wien. Leitgeb developed the new material processing technology as part of his dissertation with Professor Ulrich Schmid in cooperation with CTR Carinthian Tech Research AG and sponsored by the Competence Centers for Excellent Technologies (COMET) program.“The porous structure influences the manner in which light waves are affected by the material. If we can control the porosity, this means we also have control over the optical refractive index of the material.” This can be very useful in sensor technology – for example, the refractive index of tiny quantities of liquid can be measured using a porous semiconductor sensor, thus allowing a reliable distinction between different liquids. Another attractive option from a technical and application-oriented perspective is to first make certain areas of the SiC wafer porous in a highly localized manner, before depositing a new SiC layer over these porous areas, and then causing the latter to collapse in a controlled manner – this technique produces microstructures and nanostructures which can also play a key role in sensor technology.  However, in all these techniques it is crucial that the appropriate starting material is selected. “Until now, silicon has been used for this purpose, a material with which we already have a lot of experience”, says Professor Schmid. Silicon also has significant drawbacks, however; under harsh environmental conditions, for example in extreme heat or in alkaline solutions, structures made of silicon are attacked and rapidly destroyed. Therefore, sensors made of silicon are often not suitable for biological or electrochemical applications. For this reason, at TU Wien, attempts have been made to achieve something similar with the semiconductor silicon carbide, which is biocompatible and considerably more robust from a chemical perspective. Some special tricks were required, however, in order to produce porous structures from silicon carbide. THE COLOR-SELECTIVE MIRRORFirst, the surface is cleaned, and then partially covered with a thin layer of platinum. The silicon carbide is then immersed in an etching solution and exposed to UV light, in order to initiate the oxidation processes. This causes a thin porous layer – initially 1μm thick – to form in these areas that are not coated with platinum. An electrical charge is then also applied in order to be able to precisely set the porosity and the thickness of the subsequent layers. Here, the first porous layer promotes the formation of the first pores when the electrical charge is applied.“The porous structure spreads from the surface further and further into the interior of the material”, explains Markus Leitgeb. “By adjusting the electrical charge during this process, we can control what porosity we want to have at a given depth.” In this way, it was possible to produce a complex layered structure of silicon carbide layers with higher and lower levels of porosity, which is finally separated from the bulk material by applying a high voltage pulse. The thickness of the individual layers can be selected such that the layered structure reflects certain light wavelengths particularly well or allows certain light wavelengths to pass through, resulting in an integrated, color-selective mirror. “We have thus demonstrated that our new method can be used to reliably control the porosity of silicon carbide on a microscopic scale”, says Ulrich Schmid. “This technology promises many potential applications, from anti-reflective coatings, optical or electronic components and special biosensors, through to resistant supercapacitors.” 

SummarySome electornic or electrical appliances needs time limited power supply,or usage of some devices are depends on limitted time.To automate electrical devices depends on time simple and robust solution given based on arduino.Today let's make a arduino variable time relay together.By using this arduino variable timer relay we can control high voltage electrical appliances or electronic devices.Now let me share the process. To indicate the time duration and status 16×2 LCD display is included in this design, once the program uploaded to the Arduino then it can work independent with some external battery power source. Connection DiagramConstruction and Working In this project arduino uno board is used to control SPDT (Single pole double throw) Relay and 16 x 2 character LCD indicates the time duration status. Digital pins D2 to D7 are connected to the LCD display. VR1 varible resistor helps to control the contrast of LCD display, Transistor Q1 BC547 reacts as a Switching device and controls the power supply to the Relay coil depends on arduino output. There are three push buttons are placed to set different time durations, S1 Switch makes the count start, S2 changes the Hours and S3 changes the Minutes of time duration. Output signal from the Arduino is taken from D8 pin and it drives the Relay through transistor. After making the connection, upload the following arduino sketch and pretest the operation with real timer clock.Note:- Candle with extreme care if you using High voltage supply at the Relay end. Arduino Code #include <LiquidCrystal.h>LiquidCrystal lcd(7,6,5,4,3,2);const int set = 9;int hours=10;int start=11; int relay=8;int b=0,h=0,t=0;int buttonState = 0; int lastButtonState = 0; void setup() {    pinMode(set,INPUT);  pinMode(hours,INPUT);  pinMode(relay,OUTPUT);  pinMode(start,INPUT);  lcd.begin(16,2);  lcd.setCursor(0,0);  lcd.print("Adjustable Timer");  }int timer( int b,int h){         if(b<=9)           {            lcd.setCursor(3,1);            lcd.print(0);            lcd.setCursor(4,1);            lcd.print(b);          }     else{lcd.setCursor(3,1);lcd.print(b);}         lcd.setCursor(2,1);         lcd.print(":");     if(h<=9)           {            lcd.setCursor(0,1);            lcd.print(0);            lcd.setCursor(1,1);            lcd.print(h);          }     else{lcd.setCursor(0,1);lcd.print(h);}    }void loop()       {           buttonState = digitalRead(set);                         if (buttonState != lastButtonState)       {                 if(buttonState == HIGH)         {                       lcd.clear();           lcd.print("Set time in min:");                      ++b;           timer(b,h);                                   }                   lastButtonState = buttonState;          }       if (digitalRead(hours)== HIGH)          {              lcd.clear();              lcd.print("Set time in hours");              ++h;              timer(b,h);              while(digitalRead(hours)==HIGH);                                    }             if(digitalRead(start)==HIGH)          {             lcd.clear();             t=((h*60)+(b))*1000;             lcd.print("Timer is set for");             timer(b,h);             digitalWrite(relay,HIGH);             delay(t);             digitalWrite(relay,LOW);             while(digitalRead(start) == HIGH );                                   }                        } Have you make it successfully?  

  This article will be divided into three parts--individual transformer , parallel transformer and redundancy requirements for bulk power transformers.     Catalog   I. Individual Transformer II. Parallel Transformer III. Redundancy Requirements for Bulk Power Transformers FAQ   I. Individual Transformer   Just see the following picture, it includes the protection for banks where fuses are used on the primary. Overall differential protection may be applied by using CTs in the transformer primary bushings for larger or important banks. The common connection is shown with delta on the source (primary) side and wye-grounded on the secondary side. Other possible connections: delta–delta, wye–wye, or primary-wye– secondary-delta. Figure 1 – Transformer protection without primary-side circuit breaker   About the analysis of power circuit, you can see the article: Analysis of Switching Power Supply Principle   Note: Secondary circuits should have 51 and 51N relays. Therefore, transformer secondary breaker and relays may be omitted unless another source connects to the secondary bus. 51N relay can be omitted with 51G available.   For transformer banks with primary breakers, the protection is summarized in Figure 2.   Relay 51G provides backup protection for secondary bus and feeder faults and must be time-coordinated, with other ground relays protecting the various feeder circuits on the secondary bus. Similarly, phase relays 51 must be coordinated with the phase relays on the feeders. The common connection is shown with delta on the source (primary) side and wye-grounded on the secondary side. Other possible connections: delta–delta, wye–wye, primary-wye– secondary-delta, three-winding, or autotransformer.   Figure 2 – Transformer protection with primary-side circuit breaker   "52S may be omitted in some applications requiring 151G to coordinate with and trip the secondary circuit devices if used." II. Parallel Transformer   The protection for transformer banks where the secondaries are connected together by a bus tie breaker is summarized in the following picture(a,b,c).   The arrangement shown is typical for large- or critical-load substations, especially for industrial plants. The loads are supplied from separate buses that are connected together by a bus tiebreaker (52T) that may be operated either normally closed (NC) or normally open (NO).   Figure 3a – Single line diagram of transformer and secondary bus protection for a typical double-source supply with secondary tie and breaker   If you operated NO, the protection of the first picture and second is applicable. If operated with 52T NC, the protection of the first picture and second is applicable with the secondary side modified. Figure 3b – Secondary protection with high-side fuses With the bus tiebreaker closed, there is a possibility for the interchange of power between the two sources. Here, current flows from one source through its transformer, the secondary buses, and back through the other transformer to the second source. Generally, this is neither desirable nor permitted.   "To prevent this operation, directional time–overcurrent relays (67, 67N) are applied to each transformer."   Figure 3c – Secondary protection with high-side breaker The single-line connections are shown in Figure 3b and Figure 3c, with complete three-line connections in the following figure.   Note: They operate only for fault current that flows into the transformer and trip the secondary breaker (52–1 or 52–2). This is also important in removing a secondary fault source for faults in the transformer bank. The phase relays (67) can be set on a low of the minimum tap.   Load current certainly flows through the relay, but normally not in the operating direction. The low tap continuous rating must not be exceeded by increasing the maximum load current. The 67-time setting must coordinate with the protection on the transformer primary. When used, the ground relay can be set on minimum setting and time, because coordination is not necessary.   Figure 4 – Three-line connections for reverse-phase and partial differential backup protection The inverse-time–overcurrent relays (51, 51N) provide bus protection and backup protection for the feeder circuits. These relays trip both 52–1 (or 52–2) and 52T. This is a partial differential connection and these units must be time-coordinated with the protection on the several feeders that are connected to the bus.   "Only two-phase relays are required, but the third relay (shown optionally in Figure 4) provides additional redundancy. When a ground differential is used, as illustrated in Figure 3c, 67N and 51N are omitted."   Ground-fault backup is provided by 51G, 151G, and 251G inverse-time overcurrent relays (Figure 3abc). Relay 251G provides bus ground-fault protection and backup for the feeder circuit ground relays. It must be time- coordinated with these. It trips the bus tie 52T, as the fault could be either on the bus or on the associated feeders.   If the fault continues to exist with the bus tie open, relay 151G trips breaker 52–1 (or 52–2). Thus, 151G must coordinate with 251G. If the fault persists, it is between the secondary breaker, in the transformer winding, or in the grounding impedance.   Relay 51G set to coordinate with 151G is the last resort. It trips the high-side or primary breaker to remove the transformer from the service.   III. Redundancy Requirements for Bulk Power Transformers   When transformers are connected to bulk power systems, redundancy requirements for related protection need to be addressed. To provide the required redundancy, two separate differential schemes may be applied.   "Redundancy for transformer faults may also be obtained by a differential scheme and sudden pressure."   In such an application, the sudden pressure protection needs to be supplied with additional protection for faults on the transformer bushings and leads, as sudden pressure devices will not respond to faults in these areas. Redundant schemes for disconnecting the transformer from the system when a high-side breaker is not applied can be obtained by using various combinations of the methods. Take an example, two separate transfer trip systems may be applied although they are expensive. A cheaper alternative is to combine a transfer trip scheme and a faulty switch. It may be possible to delay closing the fault switch for a few cycles to allow time for the transfer trip scheme, provided it is operational, to de-energize the failed transformer before the closing of the fault switch. This would spare the power system from being subject to a solid fault when the fault switch closes, whenever the transfer trip scheme works properly.   When a high-side breaker is applied and it fails to operate, breaker failure protection is required to enable isolation of a faulted transformer. The breaker failure scheme may require the application of a fault switch, transfer trip scheme, or a second interrupting device if other local breakers are not available to isolate the transformer.   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.    

 This article is a brief introduction to contactor.  Catalog  I. What is a Contactor?II. Differences Between Contactor and RelaysIII. Contactor Working PrincipleIV. About Arc SuppressionFAQ I. What is a Contactor? As an essential part of the motor control gear, the most widespread switching device used in a starter is the a,c. airbrake contactor which consists of contact assemblies actuated by electromagnetic action. An operating coil is enclosed by the magnetic yoke, as well as when energized attracts an armature to which is attached a set of moving contacts which make with a set of stationary contacts. Modern contractors use a silver alloy contact tip, normally silver–cadmium oxide or silver–tin oxide alloy attached to a brass or copper backing strip. The choice of tip material is critical and is normally established after many types of tests.  Note: The rating of the contactor depends on the size, shape, and material of the contacts and on the efficiency of the arc extinction method used. An electrical contactor is an electromagnetic switch similar to a relay. It is a switch that can be controlled with the current/pulse to switch over an electrically powered circuit. II. Differences Between Contactor and Relays Let me put forward a basic question firstly:If you see in industrial control panels, both relays and contractors are used for the same purpose, so why different names? Both of them perform the same task. The relay is usually used in low voltage paths such as switching tube-light or small LEDs. The contactor is used in electrical circuits of industrial motors or other heavy applications. So, the difference is from an application point of view. The basic working principle is the same for both. The relay behaves similarly to how a contractor works. If you want to switch circuits with high voltages, use contactors and if you want to switch light voltages then the relay is ready for you.  It is important to note here the difference between protection and switching. A relay is a protection device whereas a contactor cannot assure you about protection. The relay can differentiate between normal & abnormal conditions and give command accordingly which contactor cannot. Switching means to break and make a circuit and a contactor is mainly used for that purpose. III. Contactor Working Principle When the contactor coil is de-energized, gravity or a spring returns the electromagnet core to its initial position and opens the contacts. For contactors energized with alternating current, a small part of the core is surrounded by a shading coil, which slightly delays the magnetic flux in the core. The following video will help you understand the working principle of contactor more intuitively:  IV. About Arc Suppression Most motor control contactors at low voltages (600 volts and less) are air brake contactors; air at atmospheric pressure surrounds the contacts and extinguishes the arc when interrupting the circuit. Modern medium-voltage AC motor controllers use vacuum contactors. High voltage AC contactors (greater than 1,000 volts) may use a vacuum or an inert gas around the contacts. High voltage DC contactors (greater than 600V) still rely on air within specially designed arc-chutes to break the arc energy. High-voltage electric locomotives may be isolated from their overhead supply by roof-mounted circuit breakers actuated by compressed air; the same air supply may be used to "blow out" any arc that forms.Without adequate contact protection, the occurrence of electric current arcing causes significant degradation of the contacts, which suffer significant damage. An electrical arc occurs between the two contact points (electrodes) when they transition from a closed to an open (break arc) or from an open to a closed (make arc). The break arc is typically more energetic and thus more destructive. Without adequate contact protection, the occurrence of electric current arcing causes significant degradation of the contacts, which suffer significant damage. An electrical arc occurs between the two contact points (electrodes) when they transition from a closed to an open (break arc) or from an open to a closed (make arc). The break arc is typically more energetic and thus more destructive.FAQ 1. What is the main function of contactor?Function of contactor, generally used for connected and disconnected of electric current supply. Usually in use for applications: motors, heater, lighting or electric power distribution. 2. Why do we need contactors?Contactors are used for high power applications. They allow a lower voltage and current to switch a much higher power circuit, so they are generally larger and more heavy-duty than control relays, enabling them to switch higher power loads on and off for many thousands of cycles. 3. How a contactor is wired?Break your circuit, L N E through your contactor. Link a permanent live and a neutral from your supply to your coil (Al + A2) then use your switch feed to your photocell from A1, and switch the wire to the switched phase of your contactor load. This should now open when light, close when dark. 4. What is NO and NC In Contactor?Normally Open (NO) and Normally Closed (NC) terms refer to type of dry contact or wet contact. Put very simply, a Normally Open sensor will have no current when in a normal state but when it enters an alarm state it will have +5V applied to the circuit. 5. How many types of contactors are there?The contacts are classified as power contact, auxiliary contact, and contact spring. There are two types of power contact; stationary contact and movable contact. The material used for the contacts has stable arc resistance and high welding resistance. 6. Why contactor is used?Contactors are used for high power applications. They allow a lower voltage and current to switch a much higher power circuit, so they are generally larger and more heavy-duty than control relays, enabling them to switch higher power loads on and off for many thousands of cycles 7. What is the difference between a relay and a contactor?A contactor joins 2 poles together, without a common circuit between them, while a relay has a common contact that connects to a neutral position. Additionally, contactors are commonly rated for up to 1000V, while relays are usually rated to only 250V. 8. What are the types of contactors?There are different types of contacts in a contactor, and they are; auxiliary contact, power contact, and contact spring. The power contact has two types that are; stationary and movable contact. Material for making contacts must have a high welding resistance and stable arc resistance. 9. What are the three major parts of a contactor or relay?There are three major parts of a contactor or relay: the coil, mechanical linkage and contacts. The coil is used to create a magnetic field and is rated based on voltage (24 V, 120 V, 208/204 V, 480 V). The mechanical linkage connects the armature to the contacts when the coil is energized, completing the circuit. 10. How contactor is connected?A contactor is typically controlled by a circuit which has a much lower power level than the switched circuit, such as a 24-volt coil electromagnet controlling a 230-volt motor switch. Unlike general-purpose relays, contactors are designed to be directly connected to high-current load devices. 

SummaryChristmas is coming,as well as the New Year's Day. In keeping with the festive lighting of the holiday season,there are various LED lighting architecture in the world. Now let me take you to tour the landmarks lit with LEDs.  In the touring of this LED architecture, I will also introduce how this landmarks be done. Well,these These attention grabbing displays are dependent on products that can deliver a wide range of colors, and a control scheme that allows lighting designers to fully realize their creative ideas. First Stationlet's begin with the glorious Miami in Miami,Florida.  Located downtown, the Miami Tower is a 47-story landmark that you may have seen in films and on television. Before conversion to LEDs, it was lit with a total of 382 1,000 W and 400 W metal halide fixtures, with gels (color filters) applied by maintenance crews to change the color effects. Conversion to a combination of LED flood lighting and strip lighting reduced energy, maintenance, and operating costs by over a quarter million dollars annually, and the building fa?ade can now be changed to a virtually limitless combination of colors and patterns with the “push of a button”. Miami Tower and the other landmarks reviewed in this article are illuminated using Philips Color Kinetics products, which currently have a bit of a monopoly in architectural installations. The control scheme uses a data enabler to combine power with a proprietary Ethernet DMX-based data signal called KiNET, prior to routing to luminaires, junction boxes, and/or strings of strip lights.Over 16 million color combinations can be achieved through the 8-bit channels of Red/Green/Blue/White or Red/Green/Blue/Amber luminaires. A number of different controllers can be used to program either static or dynamic displays. DSP techniques ensure that data corruption is negligible even in noisy, high-EMI environments, e.g., adjacent to powered radio antennas.  Second StationLet's travel across the country to the San Francisco-Oakland Bay Bridge.  The Bay Lights of the San Francisco-Oakland Bay Bridge, installed in 2013 in what was meant to be a two-year run to celebrate the bridge’s 75th anniversary, is currently the largest LED lighting sculpture in the world. With over 25,000 white LED nodes installed on the 1.8 mile western span, the bridge surpasses even the Eiffel Tower in number of LEDs.This lighting system uses light strands,each made up of 50 individually controllable nodes designed to operate in the demanding environment conditons of the bridge--rain,vibration,wind and even road debris. Control software scans the installation to ensure that all lighting is operational Bridge lighting projects are the most challenging to implement according to Philips, because the process can include not just lighting designers, architects, and contractors, but also transportation authorities and the Coast Guard, each with separate concerns and requirements. In addition, lighting installation usually requires workers to hang from suspended cables, and to work at night to minimize traffic impact. Doesn't that sound like fun?  Third StationThis is the season to be shopping,so let's envy the lucky folks in Philadelphia who get to spend time at the appropriately named Lit Brothers Building.  Listed on the National Registry of Historic Places in 1979, the Lit Brothers Building takes up a full city block with its mix of retail and office space. Unlike newer installations, preservation of the historic and structural aspects of the building were paramount in the lighting design, which includes both flood lights and light strips to illuminate the fa-ade and ornamental columns.As engineers, we’re interested in the technical and practical details of these LED projects, like lower operating costs and reduced maintenance requirements, but the non-energy benefits these projects bring can be even more significant. They play a tremendous role in creating a space that local residents and tourists look forward to visiting, enhancing the sense of fun and excitement in the community and the economic boost that often goes with it. Fina Station   The Bai Chay Bridge stands 50 m (164 ft) over Ha Long Bay, one of the most popular and beautiful tourist sites in Vietnam. In 2000, Ha Long Bay was nominated as one of the new seven natural wonders of the world, and in 2004, Ha Long Bay hosted almost 3 million tourists due to its geological value and natural beauty. Scattered across this bay are 1,969 islands, beautiful emerald waters, and with the Bai Chay Bridge, an edition in 2006, a new landmark in Vietnam.The Bai Chay Bridge has the widest width of any cable-stayed, single-plane concrete bridge in the world. The bridge was built to improve traffic conditions and adopt Japanese construction technologies. To make this landmark even more beautiful, the Bai Chay Bridge is now illuminated in colorful LED lights that reflect off the bay waters at night.LED lights were chosen due to their dynamic capabilities, long useful life and energy efficiency. In order to achieve all the goals the investor had set, Philips supplied an environmentally-friendly LED lighting solution for its high efficiency and dynamic and elegant lighting effects.The designers installed ColorReach Powercore gen2 and ColorReach Compact Powercore from Philips Color Kinetics to illuminate the cables and pillars that run high above the bridge, as well as to highlight the dramatic beauty of the bridge’s architecture. ColorGraze MX4 Powercore was used to illuminate the bottom of the bridge, and Archipoint iColor Powercore was used in a direct view application along the spans of the bridge. ConclusionSuch beautiful LED lighting architectures around the world create beauty, enhance entertainment and transform public spaces  for human being and nature. What's more,they witness the LED light's development and become an important milestone in the history of LED lighting.