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The split core current transformer has a unique advantage in terms of ease of use, especially in field measurement occasions where interruption is not allowed. It is almost a fixed choice. The split core current transformer on the market are mainly based on the Hall principle or Rogowski coil. Due to the working principle, the accuracy is generally not high, and can only achieve about 1%. In fields such as power measurement, a large number of products with an accuracy level of 0.1% or higher are required, but the current products cannot meet the performance requirements.At present, the full-scale accuracy of our SCI series of split core transformer is 0.1% and 0.02%, and the range covers 100A to 5000A. The measurement frequency range is from DC to hundreds of kHz. High-precision split core current transformer.   II. Design principle of split core current transformer Traditional split core current transformer, whether based on the Hall principle or Rogowski coil, theoretically cannot achieve high accuracy. Sensors based on the Hall principle, even the non-open-loop closed-loop Hall sensors with high accuracy, have an upper limit of only about 0.3%. If they are made into open-loop ones, the accuracy will be further reduced. The disadvantage of Rogowski coils is also low accuracy. Flexible Rogowski coils can only achieve 1%. There are other obvious disadvantages, such as inability to measure DC, poor low-frequency characteristics, poor waveform quality, and obvious phase delay. High-precision split core current sensors, which belong to a type of direct coupled current transformer (DCCT), are a new generation of isolated current measurement devices that can measure DC, AC or pulse currents and have high-level test accuracy. In addition to the advantages of isolated measurement, it also has a series of significant advantages such as wide measurement dynamic range, extremely high measurement accuracy, wide bandwidth, fast response speed, and basically not affected by external environment such as temperature. Compared with the previous generation of Hall resistance current sensors, its performance has been qualitatively improved. The basic principle of our SCI series sensors is based on the new magnetic modulation zero flux technology. By driving the feedback current to compensate for the influence of the bus current on the magnetic ring, the zero flux state in the magnetic ring is measured, and the nearly ideal bus current-output current ratio is achieved. The SCI series of high-precision split core current sensors apply the zero flux principle. Through the superior modulation and demodulation design ideas, the high performance of this series of sensors is guaranteed in principle; through efficient self-recovery logic, high reliability under complex working conditions is achieved; through the optimization of process manufacturing and processing flow, excellent product performance and ease of use are achieved.   III. High-precision open-close current sensor index test For the performance test of the SCI series of high-precision open-close current sensors, our company selected high-precision current sensors calibrated by the China Institute of Metrology and awarded with calibration certificates for comparison test. However, due to the poor intuitiveness of the comparison method, our company uses the source meter method to test it on the basis of ensuring the accuracy of the open-close current sensor, so that customers can see it at a glance. We selected the high-precision split core current sensor SCI-600 with a range of 600A and a full-scale accuracy of 0.02% for testing. As shown in Figures 3 and 4, we selected the SCS-1500AU DC large current source with a full range of 1500A and an accuracy of 0.01% independently developed by our company as the test DC current source, the eight-and-a-half-digit meter as the test meter, and the voltage range (here we selected the Vishay series resistor with a calibrated resistance of 1.000006Ω as the load resistor for testing).   IV. Advantages The SCI series split core current sensor adopts an open-close through-core structure, provides a variety of measurement apertures and ranges to choose from, and does not need to disconnect the busbar to be measured, which is convenient for installation and measurement. It is mainly used in the field of DC, AC and pulse current measurement that requires high measurement accuracy. The primary and secondary currents are isolated from each other, and the safety performance is excellent.   Performance characteristics: Open-and-close type, easy to install and measure Advanced zero-flux closed-loop current sensor Excellent linearity and accuracy Extremely low temperature drift Wide bandwidth and low response time Isolated measurement of primary and secondary sides Strong anti-interference ability

The ability to switch magnetic elements via spin-orbit-induced torque has attracted much attention recently, contributing to the realization of high-performance nonvolatile memories with low power consumption. To achieve efficient spin-orbit-based switching, new materials and novel physics are needed to obtain high charge-spin conversion efficiency, so the choice of spin source is crucial. In view of this, Professor Hyunsoo Yang of the National University of Singapore and others recently reported the observation of spin-orbit torque (SOT) switching in a bilayer consisting of 1T'-MoTe2 semi-metallic films adjacent to permalloy. Deterministic switching can be achieved at room temperature without external magnetic fields, and the current during switching is an order of magnitude smaller than the typical current in the best-performing heavy metal devices. If the contribution of the interface spin orbit is considered in addition to the overall spin Hall effect, the reason for its thickness dependence can be understood. With the help of dumbbell-shaped magnetic elements, the switching current is further reduced by a factor of three. The findings of this article show that MoTe2 has important application prospects in the field of low-power semi-metallic spin devices. Hemei Electronics is committed to the research, development, production and sales of amorphous, nanocrystalline, Permalloy cores, current transformers, and current transformer CTs. Our products have good stability and high electrical parameters. The company has multiple vacuum heat treatment furnaces, hydrogen annealing furnaces, fully automatic core winding machines, magnetic material automatic detection systems, multiple fully automatic winding machines, and other equipment and precision testing instruments. We can customize and develop microcrystalline, nanocrystalline cores, Permalloy core related products and various magnetic ring inductors for customers. Please feel free to contact us.

Inductor is one of the commonly used components in circuit design. It can form an LC filter network with capacitor C, form a freewheeling function with diodes in the buck circuit, and can also be used in LC resonant circuits. The following introduces common applications of inductors.   1. Use capacitors to form a liquid crystal filter circuit It is well known that inductors can pass DC and resist AC, because the inductance of inductors has a great relationship with the AC frequency. The higher the frequency, the greater the inductance. As shown in the figure below, it is the most commonly used circuit structure for switching power supplies, and inductors and capacitors play a filtering role. The AC ripple in the circuit will be filtered by the inductor and the capacitor C, making the back-end output smoother. This is usually used in switching power supplies or high power applications. 2. Used in DC/DC buck circuits The DC/DC buck chip has a wide input range and high conversion efficiency. The circuit principle of the DC/DC buck chip is generally realized by inductors, capacitors and diodes. As shown in the figure below, it is an ordinary DC/DC power chip, in which the inductor and diode constitute the freewheeling function. When the internal MOS tube is turned on, the inductor stores energy; when the internal MOS tube is turned off, the inductor can power the load. This is also the most commonly used PWM step-down principle at present. 3. Used in LC resonant circuit LC can form series resonance or parallel resonance, also called frequency selection, that is, among many input frequencies, only those consistent with the resonant frequency can pass. This circuit is often used in broadcasting, television and other applications. When designing an LC resonant circuit, a lot of calculations are required to determine the optimal parameters of inductance and capacitance. A magnetic ring inductor is a coil with a magnetic ring. Because the coil has an inductive reactance to alternating current after being energized, it constitutes an electronic component-inductor! Its inductance value ranges from zero point zero to ten millisin. Originally, only coils can constitute inductance, but in order to increase inductance and reduce the volume and DC resistance of the wire, a ferrite core with the smallest eddy current loss is added. For example, if a magnetic core with a magnetic permeability of 100 is added to a coil of 1 micron, the inductance theoretically increases 100 times to 100 micron. But the actual increase is not only the magnetic permeability, but also related to the shape of the magnetic core (in addition to the ring, there are also cylindrical, square, bar, Wangzi, mouth-shaped, etc.). High-frequency AC circuits generally use magnetic core inductors below tens of millimeters. The inductance of AC circuits below a few hundred hertz is above a few hundred millimeters-enjoy. It is not suitable to use magnetic cores, microcrystalline, slope film alloy, or even silicon steel sheets! The volume and weight are much larger! Do not add iron cores where the inductance quality Q is extremely high. Inductor components are mainly used in resonant circuits, bandpass filters and bandstop filters. According to the design requirements, the circuit consists of a tuning circuit, a frequency selector, a notch filter, a filter, a high-frequency and medium-frequency transformer, an anti-interference circuit, a damping circuit, a spark extinguishing circuit, an energy storage circuit, a bridge, etc. Commonly used for filtering and anti-interference!   Hemei Electronics is committed to the research and development, production and sales of amorphous, nanocrystalline, permalloy, silicon steel core, current transformers, energy harvesting CT and electromagnetic shielding shells. The products have good stability and high electrical parameters. If you need these products, please feel free to contact us.

Before figuring out the difference between common mode inductors and differential mode inductors, it is important to first figure out what common mode current and differential mode current are.   　　Differential mode current: A pair of signals of the same magnitude and opposite direction on a pair of differential signal lines is generally the working current in the circuit, and the signal line is the current flowing between the signal line and the signal ground.   　　Common mode current: the current of a pair of signals (or noise) of the same magnitude and direction on a pair of differential signal lines. In circuits, ground noise usually propagates in the form of common-mode currents, hence the term common-mode noise. 　　In addition to eliminating common mode noise from the source, there are many ways to suppress common mode noise, but a commonly used suppression method is to filter out common mode noise by means of a common mode inductor, i.e., to keep the common mode noise outside the target circuit. That is, in-line series common mode inductor device. The principle is to increase the impedance of the common-mode loop so that the common-mode current is consumed and blocked (reflected) by the choke, thus suppressing the common-mode noise on the line.   　　Principle of Common Mode Chokes and Inductors   　　If a magnetic material is used around a pair of rings that are orientated in the same direction, a magnetic flux will be generated in the coil due to electromagnetic induction when an alternating current is passed through. Since the flux generated by the differential mode signal is of the same size and in the opposite direction and cancels each other out, the differential mode impedance generated by the magnetic rings is very small; however, since the flux generated by the common-mode signal is of the same size and in the same direction and is superimposed on each other, the common-mode impedance generated by the magnetic rings is very large. This characteristic makes the common-mode choke have little effect on the differential-mode signal, and has a good filtering effect on the common-mode noise. 　　Differential mode current passes through the common mode coil, the magnetic lines of force are in opposite directions and the induced magnetic field is weakened. The direction of the magnetic lines of force can be seen from the figure below, with the solid arrows indicating the direction of the current and the dashed lines indicating the direction of the magnetic field. 　　When the common mode current passes through the common mode coil, the magnetic lines of force are in the same direction and the induced magnetic field is enhanced. The direction of the magnetic force lines can be seen from the figure below as follows:The solid line arrow indicates the direction of the current, and the dashed line indicates the direction of the magnetic field. 　　It is well known that the inductance or self-inductance coefficient of a common mode coil indicates the ability to generate a magnetic field. For common mode coils or common mode chokes, when the common mode current flows through the coil, the magnetic flux is superimposed due to the same direction of magnetic flux, which is based on the principle of mutual inductance. In the figure below, the magnetic flux generated by the red coil passes through the blue coil, and the magnetic flux generated by the blue coil passes through the red coil, creating mutual inductance. 　　In the case of inductance, the inductances are multiplied and the magnetic chain represents the total magnetic flux. In the case of common-mode inductors, when the magnetic flux is twice the original flux, the number of turns remains the same and the current is unchanged, which means that the inductance is increased by a factor of two, and the equivalent permeability is also increased by a factor of two. 　　Why is the equivalent permeability doubled? According to the inductance equation below, the cross-sectional area of the magnetic circuit and core is constant as the number of turns n remains the same and is determined by the physical dimensions of the core, so it is constant, but the permeability u is doubled so that more magnetic flux can be produced. 　　Therefore, when a common-mode current passes through a common-mode inductor, it operates in the mutual inductance mode, where the equivalent inductance is consumed more, so the impedance of the common-mode inductor increases exponentially, which gives a good filtering effect on common-mode signals, i.e., it blocks large impedance common-mode signals and prevents them from passing through the common-mode inductor, i.e., it does not pass this signal on to the next layer of the circuit, e.g., inductive impedance ZL, which is generated by the inductor. 　　To distinguish between a common mode choke and a differential mode inductor, the most important thing is that there are several windings, a common mode choke with two windings and a differential mode inductor with one winding.   Hemei electronics is committed to amorphous, nanocrystalline, permalloy core product development, production and sales, the main products are: nanocrystalline strips, ultra-microcrystalline core, ultra-microcrystalline magnetic core, permalloy core, high power transformer core, nanocrystalline magnetic ring inductors, take the electromagnetic ring coil, split core transformer, common-mode inductor coils, precision current transformers, and other products have a good stability as well as high electrical parameters and other advantages.

Current transformer is an instrument where the current at both ends affects each other. So the question is, what is the role of current transformer? Measurement? Protection? Let's take a look at it together~~   1. The role of current transformer - Introduction Current transformer, the English name is Current transformer, the symbol is TA, is an instrument that can convert a large primary current into a small secondary current based on the principle of electromagnetic induction, consisting of a closed iron core and windings. Its structure is shown in the figure below. The primary winding has fewer turns and is connected in series in the circuit that needs to measure the current, while the secondary winding has more turns and is connected in series in the measuring surface or protection circuit. When it is in working condition, the secondary circuit of the current transformer is closed (otherwise there will be safety hazards), and the impedance of the series coil of the measuring surface or protection circuit is very small, making its working condition close to short circuit.   2. The role of current transformer 1 - Used for measurement One of the functions of current transformer is to be used for measurement, which is often used for billing or measuring the current size of running equipment. When measuring large alternating currents, in order to facilitate surface measurement and reduce the danger of directly measuring high voltage electricity, it is often necessary to use a current transformer to convert it into a more uniform current. Here, the current transformer plays the role of current conversion and electrical isolation. The current transformer converts high current into low current in proportion as required. When used for measurement, the primary side of the current transformer is connected to the primary system, and the secondary side is connected to the measurement surface or relay protection equipment.   3. The second function of the current transformer - used for protection The second function of the current transformer is to be used for protection. It is often used in conjunction with relay equipment. When the line has a short circuit or overload, the current transformer sends a signal to the relay equipment to cut off the faulty circuit, thereby achieving the purpose of protecting the safety of the power supply system. The protective current transformer is different from the measuring current transformer. It can only work effectively when the current is several or dozens of times larger than the normal current, and it requires reliable insulation, a satisfactory large accuracy limit coefficient, and satisfactory thermal stability and dynamic stability.   IV. The role of current transformer - Precautions 1. During the operation of the current transformer, the secondary side is not allowed to be open and must be kept closed. Because once the secondary side is open, the magnetic flux and the secondary side voltage will far exceed the normal value (up to thousands or even tens of thousands of volts), which is extremely harmful to the safety of operators and equipment.   2. The wiring method of the current transformer should follow the series principle, that is, the primary winding is connected in series with the measured circuit, and the secondary winding is connected in series with the measuring surface or relay device.   Hemei Electronics has been professionally developing and producing current transformers for many years. If you want to know more information, please feel free to contact us!

Introduction to the characteristics of nanocrystalline magnetic cores   On the one hand, eddy currents can be isolated, and the data is suitable for higher frequencies; on the other hand, due to the gap effect between particles, the data has low permeability and constant permeability; due to the small particle size, there is basically no crusting phenomenon, and the permeability changes with frequency are relatively stable; in addition, the powder core can be made into various shapes of special-shaped parts for use in different fields; finally, the industrial broken strip is crushed into magnetic powder and then made into magnetic powder cores, which can reduce losses and improve the use value of data. The magnetic and electrical properties of magnetic powder cores mainly depend on the magnetic permeability of the powder material, the size and shape of the powder, the filling factor, the content of the insulating medium, the molding pressure and the heat treatment process. In the future, soft magnetic powder cores will continue to follow high Bs, high μ, high Tc and low Pc. Magnetic powder cores are soft magnetic materials mixed with ferromagnetic powder and insulating medium. Because the ferromagnetic particles are very small (0.55μm is used for high frequency), they are separated by non-magnetic electrical insulating films. Low Hc, high frequency, miniaturization and thinness are developing to meet the growing trend of thin film, miniaturization and even integration of magnetic components.   Characteristics and Applications of Nanocrystalline Magnetic Cores   Nanocrystalline alloys have high saturation magnetic induction intensity. Good stability, the material becomes brittle after heat treatment, and is easy to process into alloy powder. It is possible to make new ultra-fine crystal magnetic powder cores with this alloy powder. The magnetic permeability of nanocrystalline magnetic powder cores is still very low compared with nanocrystalline magnetic cores wrapped with tape, and the soft magnetic properties are unstable. Problems currently waiting to be solved: 1. Effectively control the growth of nanocrystals during heat treatment; 2. The molding problem of magnetic powder cores; 3. The influence of heat treatment specifications on the soft magnetic properties of magnetic powder cores.   Application fields of nano-magnetic cores   In many power electronic devices, noise is the main source of interference in the circuit. Various filters are needed to reduce noise. As the main component of differential mode inductors, magnetic powder cores play a key role in filters. In order to obtain better filtering effects, the magnetic powder core material is required to have the following performance characteristics: high saturation magnetic induction intensity, wide constant magnetic permeability, good frequency characteristics, good AC/DC superposition characteristics and low loss characteristics. In response to the above requirements, soft magnetic materials for inductors, such as iron powder core, notched amorphous alloy core and iron-nickel-aluminum powder core (MPP powder core), have been developed one after another. These materials have their own advantages and functions under different application conditions. At present, UP powder core occupies a major share in the high-end market. However, due to the complex manufacturing process of M powder core, high raw material prices, and high powder core prices, its scope of application is subject to certain restrictions. In recent years, iron-based nanocrystalline soft magnetic powder cores have attracted much attention due to their low price, simple preparation process and excellent performance. Its research is quite active and is expected to replace the local use of UP powder cores and be applied in high-frequency fields.

That is what a transformer is - a magnetic flux is generated, which the Permalloy core uses to induce a current in another coil. This property, called hysteresis, causes energy losses in applications such as transformers. Therefore, "soft" magnetic materials with low hysteresis, such as silicon steel, are often used in the core, rather than "hard" magnetic materials used for permanent magnets. Soft iron cores increase the strength of the magnetic field inside the transformer.   Hence the eddy current losses. The core of a transformer is usually a full ring with two coils wrapped around it. One is connected to the power source and is called the "primary coil". The other powers the load and is called the "secondary coil". Soft magnetic materials and their associated devices (inductors, transformers, and motors) are often overlooked; however, they play a key role in the conversion of energy throughout the world.   The conversion of electrical power involves the bidirectional flow of energy between source, storage, and the grid, and is accomplished through the use of power electronics. Electric machines (motors and generators) convert mechanical energy into electrical energy and vice versa. The introduction of wide bandgap (WBG) semiconductors has enabled power conversion electronics and motor controllers to operate at relatively high frequencies. This reduces the size requirements for passive components (inductors and capacitors) in power electronics and enables higher-efficiency, higher-speed motors.   Several soft magnetic materials show promise for operation at high frequencies. As oxides, soft ferrites stand out from other magnetic materials because they are insulating and therefore good at reducing losses caused by eddy currents.  

Permalloy metal core: various types of Permalloy materials have their own different, more than silicon steel materials and ferrite excellent typical magnetic properties, has a high temperature stability and aging stability. High initial permeability class of permalloy material (IU79, IJ85IJ86) core is often made current transformer, small signal transformer; high rectangularity class of permalloy material (IU51) core is often made magnetic amplifier, bi-stage pulse transformer; low remanent magnetism class of permalloy material (IJ67h) core is often made small and medium power unipolar pulse transformer.   　　Permalloy core is mainly used for power energy harvesting, energy conversion, power measurement, leakage protection and so on. Such as: in the power system used in various types of different levels of current transformers, power energy harvesting transformers, current sensors and so on. With superior magnetic properties, in the weak magnetic field has the highest permeability, the bottom of the saturation magnetic susceptibility and high resistivity, consistent performance is better. Wide range of applications.   Hemei Electronics is committed to the amorphous, nanocrystalline, permalloy core products research and development, production and sales, the main products are: nanocrystalline strips, silicon steel cores, permalloy cores, high-power transformer cores, nanocrystalline toroidal inductors, take the solenoid toroidal coils, open-close inductors, common-mode inductors, precision current transformers, and other products have a good stability as well as high electrical parameters and other advantages.   　　The company has a number of vacuum heat treatment furnace, hydrogen annealing furnace, core automatic winding machine, magnetic material automatic inspection system, automatic winding machine, and other equipment and precision testing instruments. The annual output of nanocrystalline and Permalloy cores reaches more than 80 million. We can also develop customised silicon steel, nanocrystalline cores, permalloy cores and various toroidal inductors for our customers.   　　Based on the principle of ‘special core, professional, focus’, the company has established and implemented ISO9001:2008 quality management system. We believe that the establishment and implementation of the quality management system will help the company to continuously improve the quality of product management level, to establish a good corporate image and reputation in the market competition, the long-term development of the company is of great significance, to meet the majority of customers on the variety and quality of the various requirements. In the future, we will continue to work hard to promote our products to a wider range of areas of use.

Overview of voltage and current transformers A typical transformer uses the principle of electromagnetic induction to convert high voltage into low voltage, or convert large current into small current, to provide suitable voltage or current signals for measuring devices, protection devices, and control devices. The voltage transformer commonly used in power systems has a primary side voltage related to the system voltage, which is usually hundreds of volts to hundreds of kilovolts, and the standard secondary voltage is usually 100V and 100V/; while the current transformer commonly used in power systems has a primary side current of several amperes to tens of thousands of amperes, and the standard secondary current is usually 5A, 1A, 0.5A, etc.   1. Principle of voltage transformer The principle of voltage transformer is similar to that of transformer, as shown in Figure 1.1. The primary winding (high voltage winding) and the secondary winding (low voltage winding) are wound on the same iron core, and the magnetic flux in the iron core is Ф. According to the law of electromagnetic induction, the relationship between the voltage U of the winding and the voltage frequency f, the number of turns of the winding W, and the magnetic flux Φ is: 2. The principle of the current transformer It is also similar to the transformer in principle, as shown in Figure 1.2. The main difference from the voltage transformer is that under normal working conditions, the voltage drop on the primary and secondary windings is very small (note that it does not refer to the voltage to the ground), which is equivalent to a transformer in a short-circuit state, so the magnetic flux Φ in the iron core is also very small. At this time, the magnetic potential F (F=IW) of the primary and secondary windings is equal in magnitude and opposite in direction. That is, the current ratio between the primary and secondary of the current transformer is inversely proportional to the number of turns of the primary and secondary windings.   3. Terminals and polarity of transformer windings The voltage transformer winding is divided into the head end and the tail end. For a fully insulated voltage transformer, the voltage to the ground that the head end and the tail end of the primary winding can withstand is the same, while for a semi-insulated voltage transformer, the voltage that the tail end can withstand is generally only about a few kV. A and X are commonly used to represent the beginning and end of the primary winding of the voltage transformer, and a, x or P1, P2 are used to represent the beginning or end of the secondary winding of the voltage transformer; L1 and L2 are commonly used to represent the beginning and end of the primary winding of the current transformer, and K1, K2 or S1, S2 are used to represent the beginning or end of the secondary winding. Different manufacturers may have different numbers, usually with subscript 1 for the beginning and subscript 2 for the end.   When the induced potential of the terminals is in the same direction, they are called the same-name terminals; conversely, if the same-name terminals are connected to the same-name terminals, the magnetic flux they generate in the iron core is also in the same direction. The terminals with the same number as the beginning or the same end and the same induced potential direction are called subtractive polarity windings, and the voltage of the terminals is the result of subtracting the induced potential of the two windings. The correct number in the transformer is defined as subtractive polarity.   4. The main structural differences between voltage transformers and current transformers (1) Both voltage transformers and current transformers can have multiple secondary windings, but voltage transformers can have multiple secondary windings sharing one core, while current transformers must have independent cores for each secondary winding. There are as many cores as there are secondary windings.   (2) The primary winding of a voltage transformer has many turns and thin wires, while the secondary winding has fewer turns and slightly thicker wires. The primary winding of a high-voltage current transformer used in a substation has only 1 to 2 turns and thick wires, while the secondary winding has more turns. The thickness of the wire is related to the rated value of the secondary current.   (3) When the voltage transformer is operating normally, it is strictly forbidden to open the low-voltage terminal of the primary winding and short-circuit the secondary winding. When the current transformer is operating normally, it is strictly forbidden to open the secondary winding.   Hemei Electronics is committed to the research, development, production and sales of amorphous, nanocrystalline and Permalloy core products. Its main products include: Permalloy, silicon steel strip, silicon steel core, nanocrystalline core, Permalloy core, high-power transformer core, nanocrystalline magnetic ring inductor, electromagnetic ring coil, split-type current transformer, common mode inductor coil, precision current transformer and other products with good stability and high electrical parameters.

The studied return conductor refers to the "return conductor" actually existing in the structure of the current transformer. The composite error average error of the secondary winding of the current transformer often exceeds the design value or even exceeds the standard limit value. The main reason is is the interference from the return conductor. In order to reduce the interference from the return conductor of the voltage transformer structure itself, the secondary turns can be unevenly distributed, and additional shielding of the winding can be used if necessary.   The generation of the return conductor and the interference of the electromagnetic field caused by the current in the return conductor to the secondary winding composite error (calculation omitted)   When there is a return conductor in the current transformer, the primary electromagnetic field is no longer a uniform inscribed circle family, and local electromagnetic fields may be concentrated, destroying the uniformity of the core electromagnetic field, thereby causing interference to the composite error.   The U-shaped primary winding has two conductors. If the ring-shaped secondary winding is placed on one conductor, the other conductor and the ring conductor are the return conductors. Because the magnetic flux generated by the current in the return conductor passes through the core, the magnetic density of the core near the return conductor increases, preventing the magnetic density of the core on the return conductor side from decreasing, causing the magnetic density of each section of the core to be different.   Since most of the magnetic flux paths caused by this external electromagnetic field are through gas or other non-magnetic substances, the equivalent circuit of the core is only a small section, so its magnetic induction intensity is directly related to the magnetic permeability of gas or other non-magnetic substances, and the magnetic induction The wire is linked to the secondary winding, which increases the secondary leakage reactance under normal operating conditions. When the current transformer operates at or above the rated voltage, the magnetization curve is close to a linear shape. In this case, the error of the measurement level and the average error of the rated voltage error of the maintenance level are basically consistent with the calculated values. It can be seen from the above figure and calculation that under the conditions of the secondary load of the current transformer and its main parameters, when the current transformer operates at or above the rated voltage, the core flux density is in the parallel segment of the magnetized curve. , the magnetic permeability and magnetic flux density increase linearly, so the average error of the secondary winding rated voltage error is basically consistent with the measured value.   But when the primary current increases to a certain value, that is, under the condition of large overcurrent, as the magnetic flux density enters the saturation state, the magnetic flux density increases, the magnetic permeability decreases rapidly, and the error expands rapidly, which is very important. It may cause the error to exceed the limit value. In this case, as the magnetic flux density of the core near the return conductor side increases, that is, the local electromagnetic field is very strong, so there will be a significant difference between the average error and the measured value. When the specific primary current is less than the rated current, the magnetic flux density and magnetic permeability decrease, but the magnetic permeability decreases faster at this time, so there will also be a significant difference between the average error and the measured value.   Countermeasures to reduce return conductor interference   1. Use a method in which the secondary line turns are not evenly distributed.   Affected by the return conductor, if the turns of the secondary winding are evenly distributed, the core magnetic flux will be uneven, the composite error will be very large, and the difference between the average error and the basic measured value is very large. The use of non-uniformly distributed secondary windings can improve the magnetic flux distribution in the core, making it almost uniform, with small composite errors, and the average error is close to the measured value, thus reducing the interference from the return conductor.   The relative position of the return conductor and the core inside the voltage transformer is fixed. If a magnetic potential opposite to the return conductor's magnetic potential can be created close to the core, the return conductor's magnetic potential can be offset. According to the basic Biot-Savart law, the level of the electromagnetic field caused by the current at a certain point in the indoor space is inversely proportional to the distance between the two. It is known that the closer to the core, the smaller the required diamagnetic potential is.   The method of using non-uniform distribution of secondary wire turns can achieve this effect. The originally evenly distributed secondary wire turns are wound more on the core segment close to the return conductor side and less on the core segment away from the return conductor side. At this time, the secondary magnetic potential of the core section returning to the conductor side exceeds the magnetic potential when the normal distribution is uniform, and the resulting magnetic flux reverses the direction of the interference flux in this section of the core and returns to the conductor, thus canceling part of its effect. .   2. When installing, make sure that the middle turns of the secondary winding are close and sparse.   The secondary windings will also interfere with each other, which is likely to increase the error. The direction of the magnetic flux lines of the electromagnetic field between the windings is the same, which can cause accumulation. If the electromagnetic field distribution between the two windings is uneven, the accumulation result is likely to deviate from the uniform distribution of the secondary winding core magnetic flux, resulting in an increase in the average error and the measured value error. big.   In order to avoid this situation, the secondary winding should be installed so that the side with dense turns matches the dense side of the other secondary winding, and the thinner side matches the thinner side. There is a large gap between the transmission lines near two adjacent windings, which will cause large magnetic leakage. Paper circles can be used between the windings to reduce magnetic leakage interference.   3. When there is a TPY winding in the secondary winding, the method of lifting the paper coil can be used to reduce the interference of magnetic leakage.   Because the TPY winding has magnetic density, the magnetic flux leakage caused here is very large. In order to better prevent the interference of magnetic flux leakage, a paper ring with low magnetic permeability can be used to reduce this kind of interference. The paper ring can be raised in the middle of the secondary winding to reduce leakage. Magnetic interference. In addition, the magnetic potential at many magnetic density points of the TPY winding is poor and causes magnetic flux leakage. The installation should be at 90° with the center line of the U-shaped primary winding to reduce and balance the interference of magnetic flux leakage.   4. Use additional shielded windings   The main function of shielding the winding is to protect the ring core in the current transformer from interference from external stray magnetic flux. Shielded windings are multiple paired windings of other coil inductors on the voltage transformer core. Generally, two pairs of shielded windings with the same number of coil turns and opposite coil inductance positions are used. Each pair of windings is reversely rotated. Sex is tied together.   Their coil turns, winding direction and interface mode cause a leakage electromagnetic field in the high current transformer to be the same size as the stray electromagnetic field (the electromagnetic field generated in the core from the external current) but in the opposite direction to offset the stray electromagnetic field. Interference from electromagnetic fields. The higher section of the stray magnetic flux shields the winding. The potential difference of the magnetic induction is higher than that of the other section, shielding the equilibrium current flowing through the winding. This current demagnetizes the higher section of stray magnetic flux, and demagnetizes the stray magnetic flux in the lower section. The magnetization is increased so that the distance is not too close to the balanced level, so it is also called balanced winding.   The design of the shielded winding must comply with the following principles: the maximum magnetic induction intensity in the ring core is the least, and the shielding effect is best; the current in the shielded winding must be kept at a small level; the temperature of the surface winding part should be minimized ; The current distribution in the entire shielded winding must be kept uniform; the number of turns of the shielded winding coil should be kept as small as possible.   Result The interference of the return conductor of the current transformer is the direct cause of the composite error of the measurement level and the maintenance level. The existence of the return conductor partially concentrates the primary electromagnetic field, so that the core magnetic flux distribution of the basic structure winding is uneven, and the composite type The error characteristics have greatly deteriorated. In order to reduce the interference of the return conductor on the composite error, it is necessary to find a way to make the core magnetic flux of the winding evenly distributed.

A current transformer is a current conversion device. It transforms high voltage and low voltage currents into lower voltage currents to supply appearance and maintenance equipment and to isolate appearance and maintenance equipment from high voltage circuits. The current transformer's secondary current is 5A, which makes it safe and convenient to measure the appearance and relay maintenance equipment, and also enables it to be standardised in production.   The structure of the current transformer is composed of iron core, primary winding, secondary winding, terminal and insulation support. The primary winding of the current transformer turns less, connected in series in the demand for measuring current in the line, the flow of large measured current, the secondary winding turns more, connected in series in the measurement of the appearance or relay maintenance circuit.   　　The secondary circuit of the current transformer is not allowed to open circuit. Current transformer in operation, its secondary circuit has always been closed, but because of the measurement of the appearance and maintenance equipment series winding impedance is very small, the current transformer operation is close to the short-circuit situation, the primary current magnetising force is greatly offset by the secondary current, the total flux density is not large, the secondary winding potential is not large. When the current transformer open circuit, the secondary circuit impedance is infinite, the current is equal to zero, the primary current has completely become the excitation current, in the secondary winding seizure of a very high potential, hostage to personal safety, constitute the appearance of the maintenance equipment, transformer secondary insulation damage.   　　The secondary circuit of the current transformer must be grounded to avoid a breakdown of insulation, the secondary string of high pressure, hostage to personal safety, damage to equipment.  

The current transformer is a special transformer. Its function is to convert large current into a small standard current, and it works in conjunction with equipment such as measuring instruments, calibration instruments, and relays. This can have the effect of expanding the detection range of the instrument and improving the reliability and safety of the power circuit. The schematic diagram of the wiring circuit of the current transformer is as shown in the figure. The primary electromagnetic coil of the current transformer is connected in series in the primary main power circuit, and the electromagnetic coils of its secondary connected instruments and automobile relays are also connected in series.   Usually when people use current transformers, they mainly consider the two performance parameters of transformation ratio and accuracy.   1. Transformation ratio   The rated voltage value of the secondary side of the current transformer is 5A or 1A. Under normal circumstances, 5A is selected. Common transformation ratios for accurate measurement of current transformers are 5/5, 10/5, 15/5, 20/5, 25/5, 30/5, 40/5, 50/5, 75/5, 100/5, 150/5, 200/5, 250/5, 300/5, 400/5, 500/5, 600/5, 750/5, 800/5, etc. So how to appropriately choose the transformation ratio of the current transformer?   The "Design Specifications for Electrical Measuring Instruments in Electrical Power Installations" requires that "the selection of the detection range of pointer measuring instruments should ensure that the rated current of the power project is marked at 2/3 of the instrument scale." According to this standard, people can use the following The formula is used to calculate the transformation ratio N of the selected current transformer.   In this formula calculation, I is the maximum load current of the control loop, 0.7 means that the maximum load current is indicated at 70% of the instrument panel, and 5 is the secondary rating of the current transformer.   current. Then select the transformation ratio of the relative current transformer based on the measured transformation ratio value. For example, if I is 50A, N=14.29 can be obtained according to the calculation method, so a current transformer with a 75/5 ratio is selected.   2. Accuracy   The accuracy of the current transformer is also called precision, because the ratio deviation and angular deviation of the current transformer are unavoidable. The accuracy of a current transformer is calibrated as a percentage of the deviation limit of this ratio. For example, the maximum ratio deviation of a class 0.5 current transformer is ±0.5%. There are 0.1, 0.2, 0.5, 1, 3, and 5 levels of current transformers for accurate measurement, and 5P and 10P level two current transformers for maintenance. Under normal circumstances, choose level 0.2 for metrological verification, choose level 0.5 for precision measurement, and choose level 1 for general monitoring instruments.   In addition, people must pay attention when using current transformers: the secondary side of the current transformer must be grounded to prevent high voltage from the primary side from flowing into the secondary side, which may endanger the safety of equipment and life; pay attention to the first and second sides of the current transformer Optical rotation, optical rotation will ablate the instrument in serious cases; the secondary side of the current transformer cannot be leaded, and it is forbidden to install a circuit breaker on the secondary side to prevent the secondary side lead from magnetic induction of high voltage, endangering life and road safety.