The Kynix Blog - Power

Overview: Transportation electrification began with small electric vehicles and gradually entered into medium-duty and heavy-duty vehicle electrification. In this article, we will understand the importance of commercial vehicle electrification and the challenges ahead. Significance of Commercial Vehicles Electrification Global climate change has resulted from human-caused greenhouse gas (GHG) emissions, which have raised the earth's temperature over the past century. The 2016 Paris Agreement sought to reduce global GHG emissions in order to keep the average global warming within two °C above pre-industrial temperatures in order to combat this threat from climate change. The transportation industry, which produces nearly 25% of the world's CO2 emissions, is one of the biggest sources of GHG emissions. Road vehicles account for nearly 75% of all CO2 emissions in the transportation industry among all modes of transportation. Therefore, a crucial step in reducing direct CO2 emissions is the electrification of road transportation. Many governments have therefore established transitional plans to electrify their transportation sector by 2050. Around 10 million electric vehicles (EVs) were in use worldwide as of the end of 2020, with battery electric vehicles making up two-thirds of this total. These EVs are predominantly light passenger cars. Challenges in Commercial Vehicles Electrification Nearly 40% of the world's road transportation sector's CO2 emissions in 2015 came from commercial vehicles, and under the "business as usual" scenario, those emissions are expected to at least double between 2015 and 2050. Therefore, the electrification of commercial vehicles is a crucial research area because it offers a promising chance to significantly reduce these emissions. Due to the small size of electric vehicle batteries, their low mileage, and the lack of public charging infrastructure, the majority of studies on electrifying commercial vehicles have concentrated on the hybridization of these vehicles.  Light-duty trucks (LDTs), which have been successfully electrified without significantly altering travel habits, have been the primary focus of the initial deployment of zero-emission commercial electric vehicles (CEVs), including electric trucks (ETs). Heavy-duty truck (HDT) deployment is in the pilot stage, whereas the deployment of medium-duty trucks (MDT) is still in the early stages. According to recent studies, there have been around 2,50,000 light-duty commercial electric vehicle sales, including trucks, with a stock of close to 31,000 medium- and heavy-duty vehicles. When compared to light passenger vehicles, commercial electric vehicle adoption has lagged, which has been attributed to the unsatisfactory policies implemented in this sector. With the availability of suitable charging infrastructure that meets the charging needs of these vehicles, the possibility of electrifying commercial vehicles grows. Commercial vehicle drivers are unlikely to switch to electric vehicles if the charging process is more challenging, uncertain, and time-consuming. However, as can be seen from Table 1, there are a variety of uses for commercial vehicles, which also affects the average load, trip length, and daily mileage of these vehicles. Furthermore, compared to passenger vehicles, the operational schedules of commercial electric vehicles can affect how quickly these vehicles charge up at charging infrastructure. Table 1. Different applications of commercial vehicles. Source: IEEE AccessVMTi refers to Vehicle Miles Travelled,PTOii refers to Power Take-Off,Percentageiii The percentage of the truck population by vocations depends on California truck population. Recent Advancements in Commercial Vehicles Electrification  In contrast to diesel and alternative fuel trucks, however, recent advancements in lithium battery technology have made electric trucks both technically and financially feasible. Existing studies have examined the potential advantages of ETs over diesel trucks over a vehicle's lifetime. These studies have found that, despite the high upfront costs of ETs, they can perform at least as well as diesel trucks over their entire lifecycle, particularly if the latter have long battery lives and high annual mileage. Moreover, the use of ETs, particularly MDTs, and HDTs, has increased as a result of regulations and government incentives encouraging the use of zero-emission vehicles. With battery sizes ranging from 300 kWh to roughly 990 kWh, a number of truck manufacturers, including DAF, Daimler, MAN, Navistar, Nikola, PACCAR, Volkswagen, Volvo, Tesla Inc., and Thor Trucks, have made significant plans to electrify their MDTs and HDTs. Due to their short-range needs and compact batteries, MDTs have drawn the most attention from these announcements regarding electrification. All of the announcements have a model for medium-duty trucks, and some manufacturers, like Daimler and BYD, have already released their commercial trucks for certain markets. In their announcements, some manufacturers, including Navistar, Volkswagen, Thor Trucks, Freightliner, and Tesla Inc., have mentioned the production of HDTs.  On the other hand, a lot of businesses have started incorporating ETs into their fleets or have made an announcement regarding their procurement of ETs. For instance, Walmart Inc. reported 45 class 8 Tesla Semi HDT pre-orders for the coming year. Similar orders for electric delivery trucks were made by Amazon and Rivian in 2019, and Anheuser-Busch announced plans to use 21 HDTs from BYD in California by the end of the year. In general, commercial vehicles, such as trucks, can be divided into three groups based on their gross vehicle weight (GVW). LDTs fall into this category if their GVW is less than 3.5 tonnes (t), MDTs fall into this category if their GVW is between 3.5t and 15t, and HDTs fall into this category if their GVW is above 15t. Each category has a wide range of vehicle types appropriate for their range of occupational operations, such as long-haul freight and garbage collection trucks.  Due to policies encouraging the adoption of zero-emission vehicles and advancements in battery technology, the electrification of MDTs and HDTs has been increasingly adopted in recent years. MDT models with battery bank capacities ranging from 48.5 kWh to about 350 kWh and an estimated range of up to 400 km have been produced by numerous truck manufacturers. Many models of HDTs with battery bank capacities between 120 kWh and 1000 kWh to cover an estimated range of up to 800 km have been introduced or produced. Table 2 lists the specifications of some MDTs and HDTs that are currently advertised or reported. Table 2. Specification of some commercial electric vehicles. Source: IEEE Access The estimated range of CEVs and the availability of appropriate charging infrastructure determine whether or not they can be used to cover the daily travel distance of commercial vehicles. According to surveys, most medium-duty commercial vehicles travel an average daily distance of 80 km to 250 km, while heavy-duty commercial vehicles travel an average daily distance of up to 700 km. As a result, at locations where they park overnight or in between shifts, the reported range of medium-duty CEVs can cover a sizable portion of the daily travel distance with just one charging event per day.  However, some medium- and heavy-duty CEVs require high charging rates to be met in a single charging event over the times they are parked because of high charging requirements (such as long-haul operation, multiple-shift operation, etc.). A high percentage of the daily travel distance is covered by multiple charging events per day at various locations along commercial vehicles' routes due to the constrained capacity of some electrical power infrastructure, which restricts the charging rate of charging infrastructure. Therefore, the number of times a CEV may need to be charged each day will depend on the daily mileage of commercial vehicles, the CEV's estimated range, and the infrastructure's charging rate. Summarizing With Key Points: Some of the takeaways from the article are as follows: Transportation emits nearly 25% of the world's CO2 and GHGs. Thus, many governments have transitional plans to electrify transportation by 2050. As of 2020, there were 10 million electric vehicles (EVs), two-thirds of which were battery-electric. Light passenger cars dominate these EVs.Most studies on electrifying commercial vehicles have focused on hybridization because electric vehicle batteries are small, have low mileage, and lack charging infrastructure.If charging is difficult, uncertain, and time-consuming, commercial vehicle drivers will not switch to electrifying their vehicles.Recently, MDTs and HDTs have been electrified due to policies encouraging zero-emission vehicles and advances in battery technology.  This blog post is part of a full research article from IEEE Access.*******************************************************************************************************************************************

Introduction The introduction of grounding technology was originally a protective way to prevent electrical or electronic equipment from being struck by lightning. At the same time, it is also an effective means to protect personal safety. When the phase line (such as poor wire insulation, aging, etc.)  touches the equipment shell for some reason, dangerous voltage will be generated on the equipment shell, thus the generated fault current will flow through the PE line to the ground, thus playing a protective role. With the development of electronic communication and other digital fields, only considering lightning protection and safety in the grounding system is far from meeting the requirements. Electrical Grounding Explained | Basic Concepts Catalog Introduction Ⅰ Basic: Q&A Related to Electrical Ground Ⅱ DC Power Supply Ground 2.1 Basic Overview 2.2 DC Power Supply Ground Analysis with Diagrams 2.3 Ground Bounce for Buck Converters 2.4 Ground Bounce for Boost Converters 2.5 Summery Ⅲ Useful Concepts for Grounding Analysis Ⅳ Conclusion Ⅴ FAQ Ⅰ Basic: Q&A Related to Electrical Ground The signal between each device needs a "ground" as the reference ground of the signal. Moreover, with the complexity of electronic equipment, the signal frequency is getting complicated. Therefore, in the grounding design, special attention must be paid to electromagnetic compatibility issues such as mutual interference between signals. Otherwise, improper grounding will seriously affect the reliability of system operation. Here the following are doubts that may arise in the power grounding. Q1: What is the definition of grounding?A: As for grounding concepts, to line engineers, the term usually means "reference point for line voltage". For system designers, it is often a cabinet or rack. For electrical engineers, it means green safety ground or connection to the earth. A more general definition is "A ground is a low impedance path for current to return to its source", and the key points are "low impedance" and "passage". Q2: What are the common grounding symbols in circuit?A: PE, PGND, FG-protective ground or chassisBGND or DC-RETURN-DC-48V (+24V) power supply (battery) returnGND: working groundDGND: digital groundAGND: analog groundLGND: lightning protection ground Q3: What is the appropriate grounding method?A: There are many ways to ground, including single-point grounding, multi-point grounding and mixed types of grounding. Among them, the single is divided into series single-point grounding and parallel single-point grounding. Generally speaking, single-point grounding is used for simple circuits, while grounding distinction between different functional modules, and multi-point grounding or multi-layer boards (complete ground plane layer) are used in low-frequency (f10MHz) circuits. Q4: Why should the analog ground and digital ground be separated?A: Both the analog signal and the digital signal return to the ground, the digital signal changes fast with large noise, while the analog signal needs a clean ground reference to work. If the analog and digital grounds are mixed, noise can affect the analog signal.According to the above mentioned, the analog ground and the digital ground should be processed separately, and then connected together through thin wires, or together at a single point. The general idea is to try to block the noise on the digital ground from flowing to the analog ground. Of course, this is not a very strict requirement that they must be separated, because it depends on the actual situation. Q5: How to ground the signal on the board?A: Under normal circumstances, it is best to use the nearest ground when designing, and after a complete multi-layer board design, it is very easy to ground common signals. The basic principle is to ensure the continuity of the traces and reduce number of vias, close to ground plane or power plane, etc. Q6: How to ground the interface devices of the board?A: Some single boards have external input and output interfaces, such as serial port connectors, network port connectors, etc, if they are not properly grounded, it will also affect normal work, such as network port interconnection errors, packet loss, etc., and will become an external source of electromagnetic interference, sending the noise inside the board to the outside. Generally speaking, an independent interface ground will be divided, and the connection with the signal ground will be connected by thin traces, and a o small resistance or 0ohm resistor can be connected in series. Thin traces can be used to block signal ground noise from passing to the interface ground. Similarly, the filtering of interface ground and interface power should also be carefully considered. Q7: How to ground the shielding layer in the cable with shielding layer?A: The layer of the shielded cable must be connected to the interface ground of the single board, not the signal ground. This is because there are various noises on the signal ground. If the shielding layer is connected to the signal ground, the noise voltage will drive the common mode current along the shielding. Therefore, cables with unreasonable design are generally the largest noise output source of electromagnetic interference.   Ⅱ DC Power Supply Ground 2.1 Basic Overview In power supply design, safety is often in the first place, and the same is true in switching power supplies. Grounding can protect the personal safety of users and ensure the normal operation of power equipment. So what is the appropriate grounding method in switching power supplies? What are the common ground symbols in circuits? This article will popularize the grounding basic in DC power supplies.DC-DC is a commonly used power supply circuit in electronic hardware design. It has high efficiency in realizing high input voltage and low output voltage. It is widely used, from power adapters, mobile phone chargers, and internal power conversion of electronic equipment to DC-DC circuits. Each semiconductor manufacturer has its own DC-DC chips, and also there are many optional chips. For a well-designed DC-DC circuit, not only the peripheral resistance, capacitance, but also the inductance parameters of the DC-DC circuit should be considered. There are also high requirements for the PCB layout design. This paper proposes a method to guide the grounding in the PCB layout from the perspective of the current flow in DC circuits. 2.2 DC Power Supply Ground Analysis with Diagrams Circuit grounding looks simple in a circuit schematic, but the actual characteristics of a circuit are determined by the layout of its PCB. And the analysis of the grounding point is very difficult, especially for the DC-DC converter circuit, the grounding point of the circuit will gather a large current that changes rapidly. When grounded nodes move, system performance suffers and the system radiates EMI. Here a good understanding of the physical nature of "ground" induced ground noise can provide an intuitive understanding of ground noise reduction problems.The change of the transmission current in the ground loop will generate a magnetic field in the loop. The magnetic field strength is proportional to the current, and the magnetic flux is proportional to the product of the loop area and the magnetic field strength, which is expressed by the formula: Figure 1. Right Hand Rule Suppose there is a sudden break in the current loop, as shown in Figure 2. When the switch is turned off, the magnetic flux disappears, which will generate a large transient voltage along the wire. If part of the wire is a grounding return pin, the voltage referenced to the ground level will have a spike, resulting in a false signal in any circuit that uses that pin as a ground reference. Figure 2. Function of Start Switch The traces on the PCB circuit board are not ideal wires and have resistance. 1 ounce (oz) copper has a resistance of 500 microohms/square, so a 1 amp change in current will only produce a bounce voltage of 500uV/square -- the problem only exists if you use long thin traces or daisy chain grounds or Precision electronic circuits.The best way to reduce ground bounce in a DC-DC switching circuit is to control the magnetic flux variation—minimizing current loop area and loop area variation. The principle of DC-DC circuit buck or boost is to use electronic switches to quickly switch to charge and discharge the energy storage element to achieve voltage conversion, and at the same time change the loop area of the current in the circuit, resulting in ground bounce and electromagnetic radiation.In some cases, as shown in Figure, the current remains constant, while the switching causes a change in the loop area and therefore a change in the magnetic flux. In switching state 1, an ideal voltage source is connected to an ideal current source through an ideal conductor. In addition, current flows in a loop that includes a ground return.In switch state 2, the same current flows in different paths when the switch changes position. The current source is DC and there is no change, but the loop area has changed. A change in the loop area means a change in the magnetic flux, so a voltage is generated. Because the ground loop is part of the change loop. Figure 3. Figure Loop Area In the case of switching changes, the loop area changes. Everywhere along the wire in the lower left, when the current I1 becomes 0, a voltage is generated where the magnetic field disappears. 2.3 Ground Bounce for Buck Converters The buck converter (step-down converter) circuit is very similar to the circuit structure in Figure 3 above, and the circuit of the step-down converter is simplified, as shown in Figure. Figure 4. Step-down Converter Circuit At high frequencies, a large capacitor such as the input capacitor Cin of the step-down converter can be regarded as a DC voltage source. Similarly, an inductor such as the output inductor LBuck can be regarded as a DC current source. These approximations help to visualize understanding and theoretical analysis.As shown in Figure 5, when the switch alternates between the two positions, the change in the path through which the current flows causes a change in the magnetic flux. The large inductor LBuck keeps the output current approximately constant. Similarly, the large capacitor Cin holds the voltage approximately equal to Vin. Since the voltage across the input lead inductance does not change, the input current also remains approximately constant. Figure 5. Effect of Switch on Loop Area Although the input current and output voltage are essentially constant, when the switch is switched from position 1 to position 2, the total loop area rapidly changes by half. Loop area changes imply rapid changes in magnetic flux, causing ground bounce along the loop circuit.In practice, a buck converter consists of a pair of semiconductor electronic switches, as shown in Figure 6. Although the complex procedure increases in each figure, the analysis method for ground bounce caused by changes in magnetic flux remains simple and intuitive. Figure 6. Magnetic Flux Changes Cause Ground Bounce The fact that changes in magnetic flux create voltages along the ground loop raises an interesting question: where is the real ground? Because ground bounce means that, to some ideal point called ground (that point needs to be defined), a bounce voltage is created on the ground return trace. In a power regulator circuit, the real ground should be connected to the low-voltage side of the load. After all, the purpose of a DC-DC converter is to provide a stable voltage and current to the load. All other points on the current loop are not true ground, but the part of ground loop.Since the low-voltage end of the load is grounded and the change in the loop area is the cause of the ground bounce, then reducing the ground bounce and electromagnetic radiation, and optimizing the grounding of the circuit are to minimize the current loop area in the DC-DC circuit. Here is a way to optimize the layout. For example, the location of the input capacitor, output capacitor, and energy storage inductor reduces the current loop area. Figure shows how to carefully place the input capacitor Cin to reduce the loop area and ground bounce. Figure 7. Reduce Ground Bounce Capacitor Cin in Figure bypasses the high-side switch on the top layer of the PCB directly to both ends of the bottom low-side switch, thereby reducing the variation in loop area and isolating it from the ground return. When the switch switches from one state to another, from the bottom of Vin to the bottom of the load, there is no loop area change or switch current change. Therefore no ground bounce occurs in the ground loop.Figure is an unreasonable PCB layout. When the high-side switch is turned on, the DC current flows along the red loop of the outer ring. When the low-side switch is turned on, the DC current flows along the blue loop. It can be seen that this circuit layout produces a large loop change when the switch changes, causing a change in the magnetic flux, resulting in ground bounce and electromagnetic radiation interference. Figure 8. Unreasonable Layout For the clarity, in single-layer PCB routing, even using a second-layer monolithic ground plane cannot solve the bounce caused by grounding. Figure 9 is a simple box to illustrate that the ground plane cannot solve the problem. Here we use a double layer PCB to add a bypass circuit at the top level power line vertical. Figure 9. Ground Floor In the Figure 9 (a), the ground plane is monolithic and uncut. The top layer print current flows through the capacitor, through the via, and to the ground plane. Because AC always flows along the path of least impedance, ground return current returns to the power source around the corners of its path. So when the amplitude or frequency of the current changes, the magnetic field of the current and its loop area change, thereby changing the magnetic flux. The regularity of current flow along the path of least impedance means that ground bounce can occur even with a monolithic ground plane - independent of its conduction.In the Figure 9 (b), a properly cut ground plane limits the return current to minimize loop area, thus greatly reducing ground bounce. Any residual ground bounce voltage developed within the cut return line is isolated from the common ground plane.The PCB layout in Figure 10 uses a double-layer PCB to mount the input capacitor and two switches on islands in the ground plane. This wiring doesn't have to be the best, but it works well and speaks to key points. It should be noted that the loop area surrounded by the red and blue currents is large, but the difference between the two loop areas is small. A small change in loop area means a small change in magnetic flux—small ground bounce. However, in general, keep the loop area small. Figure 10. is just to illustrate the importance of AC current path matching. Figure 10. Converter Layout   Additionally, ground bounce along any ground loop is limited by ground cutting within ground loop islands where magnetic fields and loop areas vary. Also, it may appear at first glance that the input capacitance Cin is not located between the top-level high-side switch and the lower-level low-side switch shown in Figure 10. Although physical proximity can be fine, what really works is the electronic proximity achieved by minimizing the loop area. 2.4 Ground Bounce for Boost Converters A boost converter (step-down converter) is actually a reflection of a buck converter, as shown in Figure 11, where the output capacitor must be placed between the top high-side switch and the bottom low-side switch to minimize loop area change. Figure 11. Changes in Loop Area In the same way that a buck converter places Cvin at a critical position, a boost converter places Cvout at a key position. 2.5 Summery The ground bounce voltage is mainly due to changes in the magnetic flux. In a DC-DC switching power supply, the magnetic flux variation is caused by switching the DC current at high speed between different current loop areas. But careful placement of the buck converter's input capacitors and the boost converter's output capacitors, and a good cut of the ground plane can isolate ground bounce. Pay attention to, it is important to be careful when cutting the ground plane to avoid increasing the loop area for other return currents in the circuit.Another reasonable layout should place the real ground on the bottom layer connecting the load, which will not cause changes in loop area or current. Any other point related to conduction can be called "ground", but it's just a point along the return path.   Ⅲ Useful Concepts for Grounding Analysis If you follow the basic concepts, you will have a clear idea of what will cause ground bounce. Figure 12. shows that two conductors that are perpendicular to each other are not subject to the mutual influence of the magnetic field. Figure 12. Two Conductors Perpendicular to Each Other   The magnetic field lines created around two parallel wires carrying equal currents in the same direction traditionally cancel each other out between the two wires, so the total energy stored by the two wires is less than the energy stored by one wire alone. Therefore, the inductance of PCB wide traces is smaller than that of narrow traces. Figure 13. Two Parallel Wires with Current Flowing in Same Directions   The magnetic field lines generated around two equal conductors carrying equal currents in opposite directions cancel each other out of the two conductors, and strengthen between the two conductors. If the inner loop area is reduced, so does 4the total magnetic flux. This phenomenon can explain why the return current of the AC ground plane always flows under the trace conductors on the top layer of the bath. Figure 14. Two Parallel Wires with Current Flowing in Opposite Directions Figure 15. shows why corners add inductance. A straight wire only sees its own magnetic field, but at the corners, the magnetic field of a vertical wire is also visible. Therefore, the corners store more magnetic field energy, and their inductance is greater than that of straight wires. Figure 15. Add Inductance at the Corners Figure 16. shows that cutting the ground plane under the transmission line conductor increases the loop area by diverting the loop current, thereby increasing the loop size and contributing to ground bounce. Figure 16. Return Current Flows Along the Path of Least Impedance   Figure 17. Effect of Component Orientation   Ⅳ Conclusion Ground bounce has always been a potential problem. For monitors or TVs, it means the image is noisy, for audio equipment it means the noise floor. In digital systems, ground bounce can cause calculation errors -or even system crashes. Careful estimation of parasitic elements and simulation are effective methods for predicting the magnitude of ground bounce.First, when designing the PCB, the low-voltage side of the load should be set to true ground. Then, replace the large inductors and capacitors with current and voltage sources to simplify the circuit dynamics. Observing the current loop under each switch combination, the loops should be made to overlap, and if this is not possible, an island should be carefully cut out in the ground plane to ensure that only islands of DC inflow and outflow are present.In most cases, good grounding performance can be obtained with these efforts. If that doesn't work, the resistance of the ground plane should be considered first, then the displacement currents flowing across all switches and parasitic capacitors entering the return path. In short, no matter what circuit, the principle is the same, that is, to reduce the loop area and its difference when the switch changes.   Ⅴ FAQ 1. Does power supply need to be grounded?While it will likely be fine (I've run many computers in old houses that had no grounding), it's not advised. A static charge will build up, and depending on where it discharges may cause damage to the electronics. 2. What is the purpose of a ground wire?The ground wire offers an additional path for the electrical circuit to flow into the earth so as to not endanger anyone working with the electricity nearby in the event of a short circuit. Without ground wire, your body could instead complete the ground path and may cause shock or electrocution. 3. Which wire is ground on power supply?In a DC circuit, the convention in most of the world is that black is the “ground” and any other color carries a signal or power rail of some sort, with red and yellow being popular for power wiring, but it can really be any color on any particular connector. For example, for a typical PC “ATX” power supply. 4. What is the purpose of a ground?Grounding gives electricity the most effective way to return to the ground via your electrical panel. A grounding wire gives an appliance or electrical device a safe way to discharge excess electricity. 5. Should you ground the negative of a DC power supply?As long as both the negative terminal of the LED and the negative terminal of the battery both have good enough connections to ground then the ground will carry enough current between the two connection to complete the circuit and light the LED. The same applies in the mains electricity supply. 6. How do I know if my power supply is grounded?Insert one probe of the circuit tester into the small slot and the other probe into the large probe. If the circuit tester lights up, you have power to the outlet. Now place one probe in the small slot and the other probe into the "U" shaped ground hole. The indicator should light up if the outlet is grounded. 7. Can you ground yourself by touching PSU?It looks pretty, but it's impossible to ground yourself to a case that has no bare metal. Instead, I just installed my power supply and touched the ground prong every now and then. All that said, if all you're doing is touching a metal part on the computer, you aren't really grounding yourself. 8. Can I tie the neutral and ground together?No, the neutral and ground should never be wired together. This is wrong, and potentially dangerous. When you plug in something in the outlet, the neutral will be live, as it closes the circuit. If the ground is wired to the neutral, the ground of the applicance will also be live. 9. What is ground in DC circuit?Traditionally, "ground" is the lowest potential in a circuit, e.g. the minus side of a battery or DC supply. 10. What happens when electricity goes to ground?The majority of the energy of the lightning discharge is dissipated in the air as it travels from the clouds to the ground through the air. The remainder is dissipated in the ground in the area surrounding the location of the strike, over a fairly short distance. 11. What is difference between earthing and grounding?Earthing and grounding are similar terms. ... The main difference between earthing and grounding is that the earthing refers that the circuit is physically connected to the ground with Zero Volt Potential. But, grounding refers that the circuit is not physically connected to ground, but still has zero potential. 12. Does a DC power supply need a ground?The answer comes from the NEC section 250.162, referring to the grounding of two-wire DC systems, which includes the 5V and 24V outputs, depending on your case. ... So, the short answer for a 24V DC system is no, the output is not required to be connected to ground. 13. How do you ground a DC power supply?You ground the device by connecting a grounding cable to earth ground and then attaching it to the grounding point on the DC power supply. You must provide the grounding cables. The cable lug used on the grounding cable should have a #10 stud hole and accommodate a minimum of 12-AWG wire.

Introduction In the FOC(Field Oriented Control) algorithm, the sampling current is the basis of the algorithm implementation and a very important part. So accurate current sampling can bring better result to the algorithm. In other words, if the current sampling is accurate, it will be very helpful for the subsequent coordinate transformation to obtain required results. From this we can see the role of current sampling in the entire FOC algorithm. Understanding Field-Oriented Control Catalog Introduction Ⅰ Current Sampling Method Ⅱ Three Sampling Methods and Precautions 2.1 Single-resistor Sampling 2.2 Dual-resistor Sampling 2.3 Triple-resistor Sampling Ⅲ The Key to Sampling Ⅳ Delay Source Ⅴ Delay Type and Typical Time Ⅵ Analysis in Details 6.1 PWM Dead Time Insertion 6.2 Optocoupler Delay and Pre-Driver Delay 6.3 Transistor Switching Delay 6.4 Other Delays Ⅶ FAQ Ⅰ Current Sampling Method In motor control, the current sampling method is generally to use PWM to trigger ADC to convert. Taking SoC(System-on-a-Chip) as an example, the ADC module will be configured to automatically sample and trigger conversion. When the trigger point set by the PWM module matches, the signal will be given to the ADC module. At this time, the sampling switch in circuit will be disconnected, and then the ADC module will start to convert, and the voltage of the corresponding sampling current can be obtained after the conversion is completed. The AD value of the signal, you can use this value in the program to write and verify the algorithm. Figure 1. Current Sampling Time Ⅱ Three Sampling Methods and Precautions Current sampling is the basis of FOC, including current sensor sampling and resistor sampling. Resistor sampling is widely used for its simple and low-cost characteristics. The method includes single-resistor sampling, dual-resistor sampling, and triple-resistor sampling. 2.1 Single-resistor Sampling The biggest difference between the single-resistor and the other two methods is that it cannot obtain two current signals at the same time. Even if two current signals are obtained, there is an error in estimating the third current signal. The formula Iu+Iv+Iw=0 is conditional, that is, the three currents must be recorded at the same time. When the inductance of the motor is larger, the two currents obtained are closer to the real situation. When the inductance is small, the deviation may be relatively large. So if the inductance of the current is large, single-resistor sampling can be selected.This method requires two samplings in one PWM cycle. In this case, it is necessary to analyze the switch state in the algorithm to clarify which phase current the reconstructed current corresponds to at the time of sampling. 2.2 Dual-resistor Sampling In the case of dual-resistor sampling, the sampled two-phase current must be used directly. Even if there is a deviation, it needs to be used. This method cannot be used to calculate the third-phase current based on the other two-phase sampling like the triple-resistor sampling. That is to say, this method needs to consider the problem of the sampling window. If the sampling current is to be guaranteed to be accurate, the sampling window must be large enough. To make the sampling window large enough, the PWM waveform needs to be deformed. But this will increase the execution time of the algorithm. The advantage of this approach is to reduce a current-sense resistor and an op amp.As shown in the figure below, the front of the red circle is the oscillating area. If the sampling window is small, only the oscillating area will not be able to obtain an accurate current. To process the sampling window, you can refer to the following figure, so that the obtained current will be more accurate. Figure 2. Current Sampling Zone 2.3 Triple-resistor Sampling This method is the simpler among the three methods. It directly uses three current-sensing resistors to sample the three-phase phase current of the motor, and the result obtained in this way is relatively straightforward. Using the formula Iu+Iv+Iw=0, recalculate the phase current of one phase with a small sampling window. So that the accuracy of the result obtained is the highest, and the implementation of the following related algorithms is easier. It is the advantage of this method. However, three current-sense resistors and three op amps are used, the hardware cost will be higher than the other two.   Ⅲ The Key to Sampling The current sampling includes peak current and average current sampling. Generally, the most common is the average current sampling and its control, so there are actually two ways to sample the average current. One is that the current-sense resistor is placed on the upper bridge of the inverter bridge. The other is that the current-sense resistor of the inverter bridge is connected to the lower end of the lower bridge.The general method is the latter. The current detection circuit corresponding to this method is relatively simple, and the corresponding power consumption will also be reduced. In this case, the freewheeling current is collected at the lower end, and then we can sample at the midpoint of the lower bridge opening. At this time, the corresponding current reflects the average current, so the corresponding current control is the average.Then, if we use the three-resistor sampling method, the selected ADC module must have at least the function of simultaneous sampling of three channels. So as to ensure that the three-phase currents obtained by sampling are the currents at the same time, and at this time, to meet the condition, Iu+ Iv+Iw=0.In the case of dual-resistor sampling, there are only two sampling resistors, and the obtained current cannot use the formula Iu+Iv+Iw=0. Therefore, even if the sampling window is small, if the algorithm is not processed, the double-resistor scheme has limitations. In order to get a better adaptation to the scene, algorithm compensation must be performed on the dual-resistor method, which is also the key point of it.Similarly, for the single-resistor sampling way, the corresponding current needs to be obtained according to different switch combinations, and it needs to be sampled twice in a PWM cycle. This method cannot satisfy Iu+Iv+Iw=0, and can only be determined by an algorithm. Compensation and correction are performed, so the single-resistor method is more difficult to take. However, if the difficulty can be solved, this method is the best and cheapest one.   Ⅳ Delay Source During the development of the motor-driven FOC control, have you encountered the situation that the motor is too noisy, inefficient or even unable to operate? All of this may be due to sampling anomalies of the phase currents, resulting in the inability to reconstruct the correct three-phase currents in the FOC algorithm. Here is an analysis of a factor that affects current sampling: the delay source.In the motor drive FOC control of double-resistor sampling, the sampling point is set as the middle moment when the lower tube of the drive bridge is turned on. Note that this is the middle moment when the lower tube of the drive bridge is turned on, not the middle moment of the PWM cycle output by the MCU. There are as many as seven delay sources in this typical drive topology because the PWM is calculated from the MCU to the ADC module where the current signal is sent to the MCU. Figure 3. MCU Output Ⅴ Delay Type and Typical Time The table below details the seven sources of delay that exist in motor drive system topologies and their typical timings. These delays will be superimposed together, and the effect is that the actual output PWM waveform lags behind the PWM waveform that the MCU calculates the expected output. According to this calculation, the phase current sampling point needs to lag the middle moment of the MCU calculating the expected output PWM waveform. Delay Type Typical Time PWM Dead Time Insertion 100ns-2μs Optocoupler Isolation to Pre-driver 40ns-300ns Pre-driver Switch Delay About 50ns MOSFET Switching Time 100ns-1μs Amplifier Delay <1μs Low-pass Filter Delay 1-2μs ADC Delay 50ns-200ns   Ⅵ Analysis in Details 6.1 PWM Dead Time Insertion In the three-phase brushless motor drive system, three bridge arms are required to control the current flow of the phase line, and there are two power devices on each bridge arm, such as MOSFET and IGBT. The pair of power devices cannot be turned on at the same time, otherwise a short circuit will occur. Here MOSFET is used as a power device to illustrate. In the control, dead time must be inserted to ensure that the upper and lower MOSFETs are not turned on at the same time. Typical values of dead time may be between 100ns and 2μs, depending on various factors in the system, such as MOSFET drive voltage and type.After the required PWM waveform is inserted into the dead time, what you get is that both the PWM midpoint and the rising edge are shifted to the right. When using the FOC control algorithm calculates the proper PWM, we start seeing the first delay, recording the dead time. Figure 4. Dead Time Insertion 6.2 Optocoupler Delay and Pre-Driver Delay The signal response of the various optocouplers and pre-drivers causes additional delays between the moment the MCU controls the FTM module to output the PWM waveform and the moment the MOSFET gate is controlled. The output of the pre-driver is delayed by a period of time (Delay1) compared to the waveform output from the MCU pins. Figure 5. Delay 1 6.3 Transistor Switching Delay Through the pre-driver, the PWM waveform reaches the MOSFET transistors, but due to their inherent characteristics, all transistors take a certain amount of time to turn on and off. This delay time varies depending on the transistor type and the voltage level required to switch between on/off. Delay 2 is the total delay between the theoretical switching point (CMP2) of the phase line voltage and the instant of the actual switching point. Figure 6. Delay 2 Finally, the gate voltage reaches the level that can make the transistor turn on, the current passes through the phase line and the sampling resistor, and a voltage difference is generated across the sampling resistor. The red waveform is the phase current waveform in an ideal state. At this time, there is a total delay time between the midpoint of the PWM cycle calculated and generated by the MCU, and the "phase current midpoint shift" is shown in the figure. Figure 7. Phase Current Midpoint Shift 6.4 Other Delays As shown in the figure below, the final delay chain that affects the current sampling is formed by the amplifier slew rate, the low-pass filter on the MCU pins, and the ADC slew rate. The time marked by the red circle in the figure is the correct current sampling time. It can be seen that the phase current sampling point is greatly delayed compared with the PWM midpoint output by the FTM. Figure 8. Other Delay In all and electrical and electronic circuits, there will be signal delay problems. And it is impossible to completely eliminate them, but the impact can be reduced by selecting low-delay devices. In the motor drive, in addition to selecting the appropriate device, it is also necessary to perform software compensation for the signal delay. The precise delay time of these delay sources mentioned in the article can be obtained by oscilloscope and calculation, and the correct current sampling time can be obtained by compensating for these delays in software. In this way, the data collected at the correct moment can be used as the data source for reconstructing the three-phase current of the motor in the FOC control.   Ⅶ FAQ 1. What is FOC algorithm?Field-oriented control (FOC), or vector control, is a technique for variable frequency control of the stator in a three phase AC induction motor. 2. What is FOC drive?Vector control, also called field-oriented control (FOC), is a variable-frequency drive (VFD) control method in which the stator currents of a three-phase AC or brushless DC electric motor are identified as two orthogonal components that can be visualized with a vector. 3. What is FOC brushless motor?FOC implementation allows the BLDC motor to run more efficiently (high power factor and better light load efficiency), more smoothly (lower torque ripples) with quick dynamic response (better dynamic performance to load and speed changes). 4. What is FOC in BLDC motor?Field oriented control (FOC) is an important control approach for Brushless DC motors. It resembles sinusoidal commutation but adds a major mathematical twist. Figure 3a shows control schemes for both sinusoidal commutation and field oriented control. 5. How is Bldc phase current measured?With a BLDC motor use an ac voltmeter to measure the voltage between any 2 wires of the 3 motor wires and then convert the line-to-line voltage to the phase voltage value by dividing the line-to-line voltage by 3 =1.73. 6. Do BLDC motors have inrush current?Handle Peak Inrush Current of a BLDC Motor to protect the Power Supply. Summary: BLDC motors have a Peak current on startup which is 3x or more the rated current. The motor has a rated current of 7.3A. 7. What causes motor inrush current?When an electrical device, such as an AC induction motor, is switched on, it experiences a very high, momentary surge of current, referred to as inrush current. ...The interaction of these two magnetic fields produces torque and causes the motor to turn.

ⅠIntroduction The most common system is single-phase, which is mostly used in homes, whereas three-phase is commonly used in industrial or commercial buildings where heavy loads of power are required. Catalog ⅠIntroduction Ⅱ Three-phase Power Related Video: Ⅲ Single-phase AC Power Basics 3.1 What is Single-phase AC power? 3.2 Advantages of Single-phase 3.3 Disadvantages of Single-phase   Ⅳ 3-phase Power Explained 4.1 What is 3-phase Power? 4.2 Advantages of Three-Phase System 4.3 Disadvantages of Three-Phase System Ⅴ Why We Need 3-phase Power？ Ⅵ What Are the Differences Between Single-Phase Power and Three-Phase Power? Ⅶ FAQ   Ⅱ Three-phase Power Related Video: Three-Phase Power Explained   Three-phase Video Description: This video will take a close look at three-phase power and explain how it works. Three-phase power can be defined as the common method of alternating current power generation, transmission, and distribution. It is a type of polyphase system, and is the most common method used by electric grids worldwide to transfer power.   Ⅲ Single-phase AC Power Basics Single-phase electric power is the distribution of alternating current electric power using a system in which all of the supply voltages vary in unison. When the loads are mostly lighting and heating, with only a few large electric motors, single-phase distribution is used.   3.1 What is Single-phase AC power? Before delving into that topic, it's a good idea to first understand single-phase alternating current (AC). Single-phase alternating current (AC) power is delivered via a three-wire system consisting of one "hot" wire, one neutral wire, and one ground wire. With alternating current power, the power current or voltage reverses on a regular basis, flowing one way on the hot wire that supplies power to the load and the other way on the neutral wire. During a 360-degree phase change, a full power cycle occurs, and the voltage reverses itself 50 or 60 times per second, depending on the system in use in different parts of the world. It is 60 times or 60 hertz in North America (Hz). It is critical to note that the two current-carrying legs are always 180 degrees apart. Consider the power as riding a wave, specifically a sine wave with a defined frequency and amplitude. During each cycle, the waves on each wire pass through zero amplitude twice (see Figure 1). There is no power delivered to the load during these times. Figure1:Single-phase   These brief interruptions have no effect on residential and commercial building applications such as office environments, but they have serious consequences for the motors that power large machinery, as well as computers and other IT equipment.   3.2 Advantages of Single-phase Single-phase connections are designed for household supplies and residential homes. This is due to the fact that most appliances, such as televisions, lights, fans, refrigerators, and so on, require only a small amount of electricity to function.A single-phase connection works in a straightforward manner. It consists of a compact and lightweight unit in which the flow of electricity through the wires is reduced as the voltage increases.Because of the power reduction, it ensures that the power from a single-phase connection operates at peak efficiency and effectively transmits power.A single-phase connection is best suited for units rated up to 5 horsepower.   3.3 Disadvantages of Single-phase     Ⅳ 3-phase Power Explained Three-phase electric power (abbreviated 3), is a type of alternating current that is commonly used in power generation, transmission, and distribution. It is a type of polyphase system that uses three wires (or four if a neutral return wire is used) and is the most common method used by electrical grids around the world to transfer power.   4.1 What is 3-phase Power? As the name implies, three separate currents are provided by three-phase power systems, each separated by one-third of the time it takes to complete a full cycle. However, unlike single-phase, where the two hot legs are always 180 degrees apart, the currents in 3-phase are separated by 120 degrees. Figure 2 shows that when one line is at its peak current, the other two are not. When phase 1 reaches its positive peak, phases 2 and 3 are both at -0.5. In contrast to single-phase current, there is no point at which no power is delivered to the load. In fact, one of the lines is at a peak positive or negative position at six different points in each phase. In practice, this means that the total amount of power supplied by all three currents remains constant; there are no cyclical peaks and valleys as with single-phase. Many computers and motors used in heavy machinery are built with this in mind. Instead of having to account for the variation inherent in single-phase AC power, they can draw a steady stream of constant power. They use less energy as a result. Consider the difference between a single-cylinder and a three-cylinder engine. Both use a four-stroke engine (intake, compression, power, exhaust). With a single-cylinder engine, you only get one "power" cycle for every four-cylinder stroke, resulting in rather uneven power delivery. A three-stroke engine, on the other hand, produces power in three alternating phases (again separated by 120 degrees), resulting in smoother, more consistent, and efficient power. Figure2:Three-phase 4.2 Advantages of Three Phase System There are numerous reasons why this power is preferable to single-phase power. The single phase power equation is   Figure3: single phase power equation Which is a function that changes over time. In contrast, the three-phase power equation is   Figure4: three-phase power equation Which is a constant function that is independent of time. As a result, the single-phase power is pulsing. This has no effect on low-rated motors, but it causes excessive vibration in higher-rated motors. As a result, three-phase power is preferable for high-tension power loads. A three-phase machine has a 1.5 times higher rating than a single-phase machine of the same size. Because single-phase induction motors have no starting torque, we must provide an auxiliary means of starting, whereas three-phase induction motors are self-starting and do not require any auxiliary means. In the case of a three-phase system, the power factor and efficiency are both higher. Which is a constant function that is independent of time. As a result, the single-phase power is pulsing. This has no effect on low-rated motors, but it causes excessive vibration in higher-rated motors. As a result, three-phase power is preferable for high-tension power loads. A three-phase machine has a 1.5 times higher rating than a single-phase machine of the same size. Because single-phase induction motors have no starting torque, we must provide an auxiliary means of starting, whereas three-phase induction motors are self-starting and do not require any auxiliary means. In the case of a three-phase system, the power factor and efficiency are both higher.   4.3 Disadvantages of 3-phase Power The most significant disadvantage of a three-phase connection is that it cannot handle the overload. As a result, it may cause damage to the equipment, increasing the likelihood of costly repairs. This is due to the high cost of individual components. Because the unit voltage is so high, a three-phase power connection necessitates a significant investment in insulation. Insulation varies with voltage, and wire size is determined by power distribution.   Ⅴ Why We Need 3-phase Power？ The ability to deliver ever-increasing amounts of power is especially important as data centers and server rooms become denser. More powerful computing systems are being crammed into the same spaces that once housed servers that used a fraction of the electrical power that today's computers and networks require. Not long ago, a single IT rack of ten servers would consume a total of five kilowatts (kW). Today, that same rack may house dozens of servers, each drawing 20 or 30 kW. At those levels, efficiency is important, as even a small percentage improvement in power consumption will result in significant dollar savings over time. Another issue is wiring. Take a look at a 15 kW rack. Using single-phase power at 120 volts AC (VAC), it takes 125 amps to power the rack, which would necessitate a wire almost one-quarter inch in diameter (AWG 4) — too thick to work with easily, let alone affordably. Because three-phase is more efficient, it can deliver the same amount of power (and more) while using less wiring. To support the same 15 kW rack with 3-phase power, three wires capable of supplying 42 amps (AWG 10) are required, each less than one-tenth of an inch in diameter.   Ⅵ What Are the Differences Between Single-Phase Power and Three-Phase Power? The following are the key distinctions between a single-phase and three-phase connection. Ⅶ FAQ 1. How is 3phase power generated? Electric power is generated as three phase alternating current (AC) by turning mechanical turbines from the forces of water, steam, or other means in order to turn generators, thereby, converting the mechanical energy into electric energy. In the US, generators turn at 60 revolutions per second or at 60 hertz (Hz). 2. Why does three phase not need a neutral? A neutral wire allows the three phase system to use a higher voltage while still supporting lower voltage single phase appliances. In high voltage distribution situations it is common not to have a neutral wire as the loads can simply be connected between phases (phase-phase connection). 3. How many wires does 3 phase have? four wires Three-phase has four wires: three actives (called phases) and one neutral. The neutral wire is earthed at the switchboard. 4. How do you make 3 phase voltage? In a 3 phase system, there are three equal voltages or EMFs of the same frequency having a phase difference of 120 degrees. These voltages can be produced by a three-phase AC generator having three identical windings displaced apart from each other by 120 degrees electrical. 5. Does three-phase need a ground? Does the National Electrical Code (NEC) require a 480-volt (V), three-phase, 3-wire, delta-connected system to be grounded? No, it is optional. This article examines the NEC's electrical-system grounding provision. 6. What is the symbol for 3 phase? A three-phase system may be arranged in delta (∆) or star (Y) (also denoted as wye in some areas). 7.Is 240V single phase or 3 phase? 240V power is used in the US and parts of the world. In the US 120 / 240V 1 Phase 3 Wire is the standard for homes and 240V 3 Phase Open Delta is the standard for small buildings with large loads. In parts of the world 240V Single Phase 2 Wire is the standard for homes. 8. What is the value of 3 phase voltage? 3 phase system is expressed with line voltages. The line votage is 440 volt. Also the voltage between any one phase and neutral for a 3 phase system is 240 volts. 9. What is single-phase power used for? Single-Phase Power generates electricity to residential homes and domestic supplies, since most appliances require only a small amount of power to function, including fans, heaters, television, refrigerator, and lights. 10. Why does single phase have 2 wires? Two hot wires and one neutral wire provide the power. Each hot wire provides 120 volts of electricity. The neutral is tapped off from the transformer. A two-phase circuit probably exists because most water heaters, stoves and clothes dryers require 240 volts to operate. 11. Can we use 2 AC in single phase? You can, yes. The main MCB has a current rating of at least 25 ampere. If you use 1.5 ac, it has max load current of 7 to 8 amperes for a single ac, and the MCB size is to be selected. 12.Is 240 volt single-phase? Single Phase 120/240 It may also be called Split Phase 240. This configuration consists of 2 voltage legs that are 180 degrees apart. The voltage between the two legs (called phase to phase or line to line) is 240V and the phase to neutral voltage is 120V.  

Warm hints: The word in this article is about 2500 and  reading time is about 12 minutes. Summary In the power system, in addition to the traditional harmonic sources, such as electric arc furnace and frequency converter, the nonlinear loads such as new energy access and charging pile may produce a lot of harmonics. In order to prevent harmonic from further affecting the power grid, accurate monitoring and timely treatment of harmonic level in power grid is a necessary step. The correct measurement of harmonic content in power grid is the basis of monitoring and governance. This paper mainly introduces some basic  knowledge about capacitor voltage transformer including the capacitor voltage transformer symbol; testing; working principle; capacitive voltage transformer VS inductive voltage transformer and etc. Article core capacitor voltage transformer Abbreviation CVT English name capacitor voltage transformer Category Power Subject Power engineer compose Capacitive voltage divider and medium voltage transformer Field Energy         Catalogs I. What is Capacitor Voltage Transformer( CVT)3.1 Insulation Resistance Measurement1.1 The Composition of CVT3.2 Capacitance Measurement1.2 CTV Judgment of Common Anomalies3.3 Pressure Swing Ratio Test1.3 CVT Equivalent Circuit Model3.4 Polar MeasurementII.Terminal Sign of Capacitive Voltage TransformerIV.Working Principle of Capacitive Voltage Transformer （CVT)III.Capacitor Voltage Transformer TestingV.Capacitive Voltage Transformer VS Inductive Voltage TransformerⅥ. FAQ  Introduction I. What is Capacitor Voltage Transformer( CVT) 1.1 The composition of CVT 一、The capacitive voltage transformer is mainly composed of a capacitor voltage divider and a medium voltage transformer. The capacitor divider is made up of porcelain bushing and series capacitors installed in it. The porcelain bushing is filled with insulating oil that keeps 0.1MPa positive pressure, and steel bellows are used to balance different environments to maintain oil pressure. The capacitor divider can be used as a coupling capacitor to connect the carrier device. The medium voltage transformer is composed of a transformer, a compensating reactor, a lightning arrester and a damping device installed in a sealed tank, and the space on the top of the tank is filled with nitrogen. The primary windings are divided into main windings and fine tuning windings, and a low loss reactor is connected in series between one side and one winding. Due to the capacitance and the inherent nonlinear impedance of the capacitor voltage transformer sometimes cause Ferroresonance in capacitor voltage transformer, thus suppressing resonant damping device, damping device is composed of a resistor and reactor, connected across the two windings, normally the damping device has very high impedance, when iron magnetic resonance caused by overvoltage in medium voltage transformer affected before the reactor is saturated only resistive load, the oscillation energy will soon be reduced. 1.2 CTV Judgment of common anomalies (1)The secondary voltage fluctuation. The two connection is loose, the distributor is not grounded or the carrier coil is not connected. If the damper is a fast saturable reactor, it may be improper parameter matching. (2)The Secondary voltage is low. Its connection is bad and the electromagnetic unit failure or the capacitor unit C2 is damaged. (3)The secondary voltage is high.The capacitance unit C1 is damaged and the ground end of the partial voltage capacitor is ungrounded. (4)The oil level of the electromagnetic unit is too high. The next capacitance unit is leaking oil or electromagnetic unit into the water. (5)There is a different sound in the transportation. Bolt loosening of reactor or medium pressure rheostat in electromagnetic unit. 1.3 CVT equivalent circuit model Under the condition of steady state, the whole CVT equivalent circuit can be regarded as a linear system, which compensates the stray capacitance of reactor C. The influence of the primary stray capacitance C: of the intermediate transformer at the high frequency can not be ignored. CVT intermediate transformer core can be regarded as linear segments in the magnetization curve, ignoring the core magnetizing inductance, one or two intermediate transformer side leakage resistance reduction to compensation reactor.   II.Terminal sign of capacitive voltage transformer · A single phase transformer with a two - time winding   It represents a single-phase transformer with two times winding. A represents the primary winding terminal of capacitive voltage transformer, and N represents the primary winding grounding terminal of voltage transformer. A represents the two winding terminal terminal of a capacitive voltage transformer, and N represents the first winding grounding terminal of the voltage transformer. · Single phase transformer with two two times windings   It represents a single-phase transformer with two two times windings, A represents the primary winding terminals of capacitive voltage transformers, and N represents the primary winding grounding terminals of voltage transformers. 1A and 2A represent the two winding terminals of the capacitive voltage transformer, and 1n and 2n represent the primary winding grounding terminals of the voltage transformer. · A single phase transformer with two two windings with a tap A single phase transformer with two taps and two winding is represented. A represents the primary winding terminal of capacitive voltage transformer, and N represents the primary winding grounding terminal of voltage transformer. 1A1, 1A2, 2a and 2A2 respectively represent the two winding terminals of the capacitive voltage transformer, and 1n and 2n represent the primary winding grounding terminals of the voltage transformer. · A single phase transformer with a residual voltage winding and two two times windings   It represents a single-phase transformer with a residual voltage winding and two two winding. The A represents the primary winding terminal of capacitive voltage transformer, and N represents the primary winding grounding terminal of voltage transformer. 1A1, 1A2, 2a and 2A2 respectively represent the two winding terminals of the capacitive voltage transformer, and 1n and 2n represent the primary winding grounding terminals of the voltage transformer. Da and DN represent the residual voltage terminal.   Detail III. Capacitor Voltage Transformer Testing 3.1 Insulation resistance measurement The insulation resistance should be measured by the main capacitor, the partial voltage capacitor and the one or two winding insulation resistance of the intermediate transformer. 3.2 Capacitance Measurement The purpose of the test is to determine whether the capacitance of the voltage divider has a change, and the capacitor is insulated without water and dampness.   3.3 Pressure swing ratio test The test transformer exerts high voltage as far as possible. Due to the rise effect in the test, the high voltage voltage must be measured at the high voltage end. The voltage transformer used must be level 0.1 or above to ensure the accuracy of the test results. After the voltage is applied at the high voltage side, the voltage of the low voltage side is measured in turn on the two side and in the auxiliary side, and the voltage ratio is compared with the pressure ratio of the nameplate. 3.4 Polar measurement The purpose of polar measurement is to check the mark of the nameplate. Test method: using DC method, CAR instantaneous addition of 1.5V battery power "+", "-" with "N", respectively, with a multimeter or mA DC or mV meter, pay attention to the polarity put right, A1, A0 "+" X1, XD "-" pointer in the power supply to the deflection of the "+" direction; open to "-" deflection. The test of polarity and pressure variable ratio of windings is usually done in hand over and after overhaul.   IV. Working Principle of Capacitive Voltage Transformer （CVT) There is a video about CVT:   This vidoe explained How Capacitor Voltage Transformer CVT works.Capacitor potential transformer concept is explained.What is high voltage measurement using capacitor type voltage transformer is explained. How to measure high voltage? Educational tutorial on electrical engineering 126 by G K Agrawal. The basic part of the capacitive voltage transformer is the capacitor voltage divider, and it also includes the electromagnetic parts such as the intermediate transformer, the compensating reactor, the damper and so on. Its principle connection is shown in the following picture,the picture shows capacitor voltage transformer wiring diagram capacitance divider is composed of main capacitor C1 and voltage divider capacitor C2 series. Without considering the electromagnetic part, the voltage is divided by capacitance. The voltage on C2 is the following formula: K is the partial voltage ratio. When the two ends of the C2 are connected to the two load, due to C1, C2 The basic part of the capacitive voltage transformer is the capacitor voltage divider, and it also includes the electromagnetic parts such as the intermediate transformer, the compensating reactor, the damper and so on. Its principle connection is given below.   The capacitor voltage divider is composed of the main capacitor C1 and the partial voltage capacitor C2 in series, without considering the electromagnetic part, then the voltage is divided according to the capacitance inverse ratio, and the voltage on the C2 is:   In this formula,K is the ratio of partial pressure When the two ends of C2 are connected to two loads, the larger capacitance internal impedance is due to the existence of C1 and C2, which makes UC2 smaller than the capacitance partial voltage. The larger the load current is, the greater the error is. In order to reduce the capacitance internal impedance, a compensatory reactor L can be connected in series, and the UC2 is not related to the load as much as possible. In fact, because the capacitor has loss, the reactor also has resistance, so that the internal impedance can not be zero, so when the load changes, there will always be error. In order to further reduce the effect of load current, the measuring instrument is connected to the divider after the intermediate transformer TV is boosted. When the two side transformer short circuit occurs, the resistance in the circuit and the total reactance reactor L after compensation are very small, several times the short-circuit current may reach the rated current, will produce a very high voltage resonance in L and C2, in order to prevent overvoltage caused by the breakdown of insulation in capacitor C2 parallel at both ends of the discharge gap F1. Capacitor voltage transformer with capacitance and nonlinear inductance (e.g. TV magnetizing inductance etc.), when the transformer side suddenly close or receive two side and eliminate the impact of sudden short circuit, overvoltage in the transient process may cause nonlinear inductor saturation, which excite ferroresonance overvoltage, such as harmonic 1/3 resonant.  Because the resistance is very small, the resonance will last for a long time, which will cause damage to voltage transformers, instruments and relays, and may lead to incorrect operation of the protective devices. Therefore, the damping resistance RD or damper is often installed on the two side of the capacitive voltage transformer to consume the resonant energy as soon as possible to suppress the ferroresonance. For a common capacitive voltage transformer, a resonant damper is used. It is the capacitance and the inductor in parallel and then added to the damping resistance. In UHV power grid, a capacitive voltage transformer often uses a fast saturation type damper, which is composed of a fast saturation reactance and a damping resistor.     Analysis V. Capacitive Voltage Transformer vs Inductive Voltage Transformer Inductive Voltage Transformers (IVT), are used for voltage metering and protection in high voltage network systems. They transform the high voltage into low voltage adequate to be processed in measuring and protection instruments secondary equipment, such as relays and recorders). A Voltage Transformer (VT) isolates the measuring instruments from the high voltage of the monitored circuit. VTs are commonly used for metering and protection in the electrical power industry. It’s a standard transformer available in the market for step-up or step-down voltages. The advantage is it can be used for high load current and provides isolation.   However,as we mentioned in the above,capacitor voltage transformer is a specialized circuit whose purpose is to convert a high voltage AC signal to lower voltage, usually used with very high input voltages, and a large ratio between input and output voltage. It's usually only used in cases where you're trying to extract a very small amount of power from a high-power circuit, usually for monitoring the high-power circuit. Its advatage is economical but there is no galvanic isolation.   Ⅵ. FAQ 1. What is the function of capacitor voltage transformer?A capacitor voltage transformer (CVT), also known as capacitor-coupled voltage transformer (CCVT), is a transformer used in power systems to step down extra high voltage signals and provide a low voltage signal, for metering or operating a protective relay.   2. Why is CVT used?One of the advantages of a CVT is its ability to continuously change its gear ratio. This means that no matter what the engine speed it, it is always performing at its peak efficiency. CVTs often offer better fuel economy as a result, especially when driving in the city. ... This is because the transmission never shifts.   3. What do you understand CVT and CCVT?Capacitor Voltage Transformer (CVT) or Capacitor Coupled Voltage Transformer (CCVT) is a switchgear device used to convert high transmission class voltage into easily measurable values, which are used for metering, protection, and control of high voltage systems.   4. Why are capacitors used in transformers?At too high common mode frequencies, the inevitable capacitive coupling in the transformer will cause some of the common mode signal on the input to show up as signal on the output. The capacitor provides a more serious connection to ground for AC, while the resistor only a weak connection for DC to avoid ground loops.   5. Why is CVT hated?Because CVTs tend to lock an engine into a specific RPM, generally a high and noisy RPM, making the whole experience very hard on the ears. Also, CVTs are generally tuned for fuel economy rather than performance, and most of the magazines out there are wannabe racecar drivers.   6. What is the function of capacitor voltage transformer?A capacitor voltage transformer (CVT), also known as capacitor-coupled voltage transformer (CCVT), is a transformer used in power systems to step down extra high voltage signals and provide a low voltage signal, for metering or operating a protective relay.

Warm hints: The word in this article is about 1000 and the  reading time is about 6 minutes. MIT researchers found a way to triple the efficiency by using "topological" materials with special electronic properties. Although previous research has indicated that topological materials could be used to create efficient thermoelectric systems, little is known about how electrons in such topological materials can move in response to temperature differences to produce a thermoelectric effect. Researchers not only found that they can push the boundaries of this nanostructured material in a way that makes topological materials a good thermoelectric material,more so than conventional semiconductors like silicon,but also this could be a clean-energy way to help us use a heat source to generate electricity, which will lessen our release of carbon dioxide. NewsToday, thermoelectric devices are used for relatively low-power applications, such as powering small sensors along oil pipelines, backing up batteries on space probes, and cooling minifridges. Scientists hope to develop more efficient thermoelectric devices that will harvest heat produced as a byproduct of industrial processes and combustion engines and convert it into electricity. However, thermoelectric devices' power, or the amount of energy they can generate, is currently limited. "We discovered that we can push the limits of this nanostructured material in a way that makes topological materials a better thermoelectric material than traditional semiconductors like silicon," says Te-Huan Liu, a postdoctoral researcher in MIT's Department of Mechanical Engineering. "In the end, this could be a clean-energy way to help us use a heat source to generate electricity, which will lessen our release of carbon dioxide," Liu added. Liu is first author of the PNAS paper, which includes graduate students Jiawei Zhou, Zhiwei Ding, and Qichen Song; Mingda Li, assistant professor in the Department of Nuclear Science and Engineering; former graduate student Bolin Liao, now an assistant professor at the University of California at Santa Barbara; Liang Fu, the Biedenharn Associate Professor of Physics; and Gang Chen, the Soderberg Professor and head of the Department of Mechanical Engineering.A Path Travel Freely When a thermoelectric material is exposed to a temperature gradient — for example, one end is heated while the other is cooled — electrons begin to flow from the hot end to the cold end, resulting in an electric current. The greater the temperature difference, the more electric current and power are made. The amount of energy that can be produced is determined by the electron transport properties of a given material. Scientists have discovered that certain topological materials can be converted into efficient thermoelectric devices using nanostructuring, a technique used by scientists to create a material by patterning its features at the nanometer scale. Scientists believe that the thermoelectric benefit of topological materials stems from decreased thermal conductivity in their nanostructures. However, it is uncertain how this increase in efficiency relates to the material's inherent, topological properties.     Liu and his colleagues investigated the thermoelectric efficiency of tin telluride, a topological material considered to be a strong thermoelectric material, to try to address this issue. Tin telluride electrons also have unusual properties that resemble a class of topological materials known as Dirac materials. The researchers wanted to understand the effect of nanostructuring on the thermoelectric efficiency of tin telluride by simulating electron movement through the material. Scientists often use a calculation known as the "mean free path" to characterize electron transport. This is the average distance an electron with a given energy can freely travel within a material before being dispersed by different objects or defects in that material. Nanostructured materials resemble a patchwork of tiny crystals, each with its own boundary, known as grain boundaries, that separates one crystal from the next. As electrons come into contact with these limits, they scatter in a variety of ways. Electrons with long mean free paths scatter violently, similar to bullets ricocheting off a wall, whereas electrons with shorter mean free paths are much less affected. The researchers discovered that the electron properties of tin telluride have an important effect on their mean free paths in their simulations. They plotted the spectrum of electron energies in tin telluride against the related mean free paths and discovered that the resulting graph looked very different from that of most traditional semiconductors. In particular, for tin telluride and probably other topological materials, the findings indicate that higher-energy electrons have a shorter mean free path, while lower-energy electrons have a longer mean free path. The researchers then investigated how these electron properties influence the thermoelectric efficiency of tin telluride by essentially summing up the thermoelectric contributions from electrons with different energies and mean free paths. It turns out that the ability of a substance to conduct electricity, or produce a flow of electrons, under a temperature gradient is largely determined by the electron energy. They discovered that lower-energy electrons have a negative effect on the production of a voltage difference, and hence electric current. Since low-energy electrons have longer mean free paths, they can be dispersed more intensely by grain boundaries than high-energy electrons.Size DownGoing a step further in their simulations, the team experimented with the size of individual grains of tin telluride to see whether this had some impact on the movement of electrons under a temperature gradient. They discovered that raising the diameter of an average grain to around 10 nanometers, putting its boundaries closer together, increased the contribution of higher-energy electrons. Higher-energy electrons contribute much more to the material's electrical conduction with smaller grain sizes than lower-energy electrons because they have shorter mean free paths and are less likely to scatter against grain boundaries. As a result, a greater voltage difference can be produced. Furthermore, the researchers discovered that shrinking the average grain size of tin telluride to around 10 nanometers yielded three times the amount of electricity that the material would have produced with larger grains. Although the findings are based on simulations, Liu claims that researchers can achieve comparable results by synthesizing tin telluride and other topological materials and changing their grain size using a nanostructuring technique. Other researchers have proposed that shrinking the grain size of a material can improve its thermoelectric efficiency, but Liu claims that they have mostly assumed that the ideal size is much larger than 10 nanometers. "In our simulations, we discovered that we can shrink the grain size of a topological material far more than previously thought, and based on this principle, we can increase its performance," Liu says. Tin telluride is one of the topological materials that have yet to be discovered. If researchers can determine the optimal grain size for each of these materials, topological materials, according to Liu, can soon be a viable, more effective alternative to producing renewable energy. ConclusionLiu believes that topological materials are excellent for thermoelectric materials, and our findings indicate that this is a very promising material for potential applications. The Solid-State Solar Thermal Energy Conversion Center, an Energy Frontier Research Center of the United States Department of Energy, and the Defense Advanced Research Projects Agency contributed to this research (DARPA). Article From Proceedings of the National Academy of SciencesArticle Edited by kynix