Blog

The core of the transformer is mainly divided into two types in the power supply and distribution system: voltage transformer and current transformer. The function of the current transformer is to convert the primary current with a larger value into a secondary current with a smaller value through a transformation ratio, which is used for protection, measurement and other purposes. For example, a current transformer with a transformation ratio of 400/5 converts the actual current of 400A into a current of 5A.   The iron core plays an important role in the transformer. According to the measurement accuracy level requirements of the transformer, different soft magnetic materials can be selected as the core material. The higher the magnetic permeability or various performance requirements of the iron core, the smaller the measurement error of the transformer and the higher the accuracy. At present, the commonly used material is silicon steel sheet. The iron core of the current transformer mainly includes laminated iron core and wound iron core. The ring-shaped iron core is suitable not only for electronic transformers, but also for transformers because of its advantages such as no air gap, high magnetic permeability, low loss, less noise, and strong anti-interference. It is made of cold-rolled oriented silicon steel material that is continuously wound. The diameter, height, and width ratio of the toroidal transformer core can be changed at will as required.   At the same time, in order to protect the transformer core, it is necessary to pay attention to the following: because the working principle of the current transformer is equivalent to a transformer with a short circuit on the secondary side, it is used to convert current, and an ammeter is connected to the secondary side to measure the current. During the operation of the transformer, after the secondary side is open, the primary current remains unchanged, and the secondary side current is equal to zero, then the demagnetizing flux generated by the secondary current also disappears. At this time, the primary current is completely converted into an excitation current, which saturates the transformer core, increases the magnetic flux unprecedentedly, increases the core loss, generates high heat, damages the insulation, generates residual magnetism in the core, etc., increases the ratio difference and angle difference of the transformer, loses accuracy, or endangers the personal safety of the operator, etc. Therefore, in order to protect personal safety, the performance of the core, etc., the secondary side of the current transformer is not allowed to be open.

In order to transmit electric energy, the power system often uses AC voltage and high current circuits to send electricity to users. The role of the transformer is to reduce the AC voltage and high current proportionally to values ​​that can be directly measured by instruments, which is convenient for direct measurement by instruments, and at the same time provides power for relay protection and automatic devices. The quality of the transformer determines whether the personnel and equipment are safe, and the role of the iron core in the transformer determines its status. The working principle of the transformer is the same as that of the transformer. Both operate on the principle of electromagnetic induction, so most of the iron cores used in transformers can be used for transformer cores. Nanhai Silicon Iron Core Manufacturing Co., Ltd. produces ring cores, C-type cores, ladder cores, rectangular cores, shear/laminated cores, EI-type cores, open-wound cores and special-shaped cores, which can be used in both transformers and transformers.   The high or low magnetic permeability of the transformer core has a great influence on the measurement accuracy of the transformer. C-type core, ring core, ladder core, rectangular core, etc. are used as winding cores. They adopt oriented cold-rolled high-quality silicon steel materials to ensure the consistency of magnetic flux direction and grain orientation of silicon steel sheets. They are used in mutual inductors and have the advantages of safety, high efficiency, low noise, low loss, strong short-circuit resistance and high pressure resistance. They have always been commonly used product components in mutual inductors.

Detailed classification of bushing current transformer cores   1 Classification by purpose   1) Current transformer core (or current transformer measuring winding): Provide grid current information to measuring and metering devices within the normal voltage range.   2) Protection current transformer (or current transformer protection winding): Provide grid fault current information to relay protection and other devices under grid fault conditions.   2 Classification by insulation medium   1) Dry current transformer core: Insulated by ordinary insulating materials treated with varnish.   2) Cast insulated current transformer: Current transformer cast with epoxy resin or other resin mixed materials   3) Oil-immersed current transformer: Insulated by insulating paper and insulating oil, generally outdoor type, currently commonly used in my country at voltage levels.   4) Gas insulated current transformer: The main insulation is composed of SF6 gas. 3 According to the current conversion principle   1) Electromagnetic current transformer: a current transformer that converts current in time according to the principle of electromagnetic induction.   2) Photoelectric current transformer: a current transformer that realizes current conversion through the principle of photoelectric conversion.   4 According to the installation method   1) Through-type current transformer: a current transformer used to pass through a screen or wall.   2) Pillar current transformer: a current transformer installed on a plane or pillar and used as a primary circuit conductor pillar;   3) Bushing current transformer: a current transformer that has no primary conductor and primary insulation and is directly sheathed on an insulating bushing.   4) Busbar current transformer: a current transformer that has no primary conductor but has primary insulation and is directly sheathed on the busbar. 5 According to the number of turns of the primary winding   1) Single-turn current transformer: single-turn current transformers are commonly used for large current transformers.   2) Multi-turn current transformer: Multi-turn current transformers are commonly used for medium and small current transformers.   6 Classification by the location of the secondary winding   1) Upright type: The secondary winding is at the bottom of the product, which is a commonly used structural form in China.   2) Inverted type: The secondary winding is at the head of the product, which is a relatively new structural form in recent years.   7 Classification by current ratio   1) Single current ratio current transformer: That is, the number of turns of the primary and secondary windings is fixed, the current ratio cannot be changed, and only one current ratio conversion can be achieved.   2) Multi-current ratio current transformer: That is, the number of turns of the primary or secondary winding can be changed, the current ratio can be changed, and different current ratio conversions can be achieved;   3) Multiple iron core current transformer: This type of transformer has multiple secondary windings with their own iron cores to meet the needs of different precision measurements and a variety of different relay protection devices. In order to meet the requirements of certain devices, some of the secondary windings have multiple taps. 8 Classification by technical performance of protective current transformer   1) Steady-state characteristic type: guarantee the error of current in steady state, such as P, PR, PX level   2) Transient characteristic type: guarantee the error of current in transient state, such as TPX TPY TPZ TPS level, etc.   9 Classification by use conditions   1) Indoor current transformer: generally used for voltage level of 35KV and below.   2) Outdoor current transformer: generally used for voltage level of 35KV and above.

The national standard recommends the use of square ring and double yoke permeameter to measure the AC magnetic properties of magnetic materials, but it is only suitable for magnetic properties testing under saturated magnetic field, and cannot measure magnetic induction intensity under low magnetic field. At the same time, the American Society for Testing and Materials standard ASTM and the Russian national standard both mentioned that the toroidal transformer core sample can be used as the standard sample for material magnetic testing. For this reason, we use the wound inner diameter of 120mm as the inner diameter of the standard sample, and refer to the relevant Russian national standards to select the ratio of outer diameter to inner diameter of 1.3, and the height of the sample is set to 40mm and 100mm respectively, that is, the sample is an annular sample with an inner diameter of 120mm, an outer diameter of 156mm, and a height of 40mm and 100mm respectively (five pieces of imported A and B core materials respectively).   For ease of comparison, the representative LM363 and LMH-550 products are selected. The measurement-grade core (imported B core material, the number is five and two pieces respectively). 2.2 Test conditions   In order to make the test data more comparable with the production inspection, the test method similar to the actual production inspection is used for testing, that is, the AC test circuit is used.   2.3 Test method   (1) In the production inspection, the external magnetic field is applied to the iron core by changing the excitation current in the primary coil, and then the induced electromotive force at both ends of the secondary coil is measured, and then the magnetic induction intensity value corresponding to the current magnetic field is obtained by the following formula (1).   Uf=4.44 BSN2 f(1)   Wherein, Uf is the induced electromotive force of the secondary winding (V)   B is the calibrated magnetic induction intensity (Gs)   S is the cross-sectional area of ​​the sample (cm2)   N2 is the number of turns of the secondary winding (turns)   f is the repetition frequency of the AC magnetic field (50Hz)   (2) This paper first takes the magnetic induction intensity B as the independent variable, selects a number of data points between 0 and 20 000Gs, calculates the induced electromotive force Uf value under the current magnetic induction intensity according to formula (1), and then obtains the Uf value by adjusting the current in the primary coil, and records the excitation current value I in the primary coil at this time. Then, H at this time is obtained according to formula (2), and finally the corresponding relationship between H and B is obtained.   H=N1·I/π·Da(2)   Wherein, H is the external magnetic field strength value (A/m)   I is the primary excitation current value (A)   N1 is the number of turns of the primary coil (turns)   Da is the average diameter of the sample (cm)   3 Analysis and discussion   B40—B material height is 40mm sample   B100—B material height is 100mm sample   A40—A material height is 40mm sample   A100—A material with a height of 100mm   550—LMH-550 medium-level measurement core   363—LM363 medium-level measurement core   H—After annealing   Q—Before annealing   3.1　Material low-field magnetic analysis   A and B are imported materials of the same brand. Their low-field magnetic properties are compared as follows:   (1) Before annealing, it can be seen from Figure 2 that the low-field magnetic properties of material B are significantly better than those of A.   (2) After annealing, it can be seen from Figures 3 to 5 that from low magnetic field to medium and high magnetic field, B is significantly better than A.   3.2　Influence of core structure on magnetism   (1) Under the same inner and outer diameters, the magnetism of the material with higher height is significantly better than that of the material with lower height (that is, when the material has high magnetism, its magnetization curve is to the upper left of the magnetization curve of the material with higher magnetism), as shown in Figures 3 and 6.   (2) If the ratio of height to average diameter is used to describe the structural characteristics of the core, then   LM363 core height/average diameter = 0.057   LMH-550 core height/average diameter = 0.181   120/156*40 sample height/average diameter = 0.290   120/156*100 sample height/average diameter = 0.725   ① As can be seen from Figure 6 (within the range of 0 to 1 000Gs), for the same material, as the height-to-diameter ratio decreases from high to low, the magnetism decreases in sequence, that is, the curves of the 100-height sample, 40-height sample, and measurement-grade core are distributed from the upper left to the lower right in sequence. ② From the test (curve omitted), after exceeding 1 000Gs, the magnetization curves gradually become similar.   3.3 Comparison of magnetization curves before and after annealing   ① The magnetism of the core increases significantly after stress relief annealing after cutting and winding. ② Within the range of 1A/M magnetic field strength (i.e., within the range of 120Gs magnetic induction), the magnetism of B core material before annealing is better than that of A core material after annealing. When the magnetic field strength is greater than 20A/M, the magnetism of the unannealed core quickly tends to saturation with the increase of magnetic field strength; while after stress relief annealing, its magnetism still changes linearly under higher magnetic fields.   3.4 Comparison of magnetism between product core and sample   (1) Low magnetic field magnetism of LM363L and LMH550 measurement-grade core before annealing. (2) The low magnetic field magnetism of LM363 and LMH550 cores (wound with B material) after annealing is similar to that of the B material sample, but slightly inferior, indicating that the sample is representative.   3.5 Observation and comparison of the microstructure of the core material   (1) From the substructure of a single grain of the material, it can be seen that the cellular substructure in (B material) is more uniform and oriented than (A material in this test batch); (2) From the observation of the grain boundary of the material, it can be seen that the orientation consistency of the cellular substructure between grains is obviously better than that in Figure 9(b). Among them, B material, A material in this test batch, satisfies the A material of the measurement-grade core magnetic requirements in LM363 and LMH-550 products. (3) The microstructures with relatively poor low-field magnetic properties in the same batch of materials show that their common feature is that there are more local grain boundary protrusions and wider areas (diamond-shaped with stripes on them), which affects the uniformity and continuity of the overall organization. From the above observations and comparisons, it can be seen that in the microstructure of the core material, the cellular substructure with good and uniform orientation consistency and narrow grain boundaries has higher low-field magnetic properties.   4 Conclusions   1. Affected by the manufacturing process and process control, the low magnetic field magnetism of the core materials of the same brand but produced by different manufacturers, and the core materials of the same manufacturer in different periods are not the same; 2. The low magnetic field magnetism of material B is obviously higher than that of material A; 3. Stress relief annealing can improve the magnetism of the core, especially the magnetism of the material under the magnetic field, while the core material without annealing tends to saturate quickly under a higher magnetic field; 4. For the cores with the same inner and outer diameters, the ones with higher height have better magnetic properties; 5. In the microstructure of the core material, the ones with good and uniform cellular substructure orientation and narrow grain boundaries have higher low magnetic field magnetism.

A magnetic material with low coercivity and high magnetic permeability. Soft magnetic materials are easy to magnetize and demagnetize, and are used in electrical and electronic equipment. The most commonly used sensor cores are iron-silicon alloys (silicon steel sheets) and soft ferrites. There are many types of soft magnetic materials, which are usually divided according to their composition: ① Pure iron and low-carbon steel. The carbon content is less than 0.04%, including electromagnetic pure iron, electrolytic iron and carbonyl iron. It is characterized by high saturation magnetization, low price and good processing performance; but its resistivity is low and the eddy current loss is large under alternating magnetic fields. It is only suitable for static use, such as manufacturing electromagnetic cores, pole shoes, relays and speaker magnetic conductors, magnetic shielding covers, etc. ② Iron-silicon alloys. The silicon content is 0.5% to 4.8%, and it is generally made into thin plates for use, commonly known as silicon steel sheets. After adding silicon to pure iron, the phenomenon that the magnetic properties of magnetic materials change with the use time can be eliminated. As the silicon content increases, the thermal conductivity decreases, the brittleness increases, and the saturation magnetization decreases, but its resistivity and permeability are high, and the coercive force and eddy current loss are reduced, so it can be applied to the AC field to manufacture the iron cores of motors, transformers, relays, mutual inductors, etc. ③ Iron-aluminum alloy. Containing 6% to 16% aluminum, it has good soft magnetic properties, high magnetic permeability and resistivity, high hardness, good wear resistance, but brittleness. It is mainly used to manufacture iron cores and magnetic heads of small transformers, magnetic amplifiers, relays, etc., ultrasonic transducers, etc. ④ Iron-silicon-aluminum alloy. It is obtained by adding silicon to the binary iron-aluminum alloy. Its hardness, saturation magnetic induction, magnetic permeability and resistivity are all high. The disadvantage is that the magnetic properties are sensitive to composition fluctuations, the brittleness is large, and the processing performance is poor. It is mainly used for audio and video heads. ⑤ Nickel-iron alloy. Nickel content is 30% to 90%, also known as Permalloy. Through alloying element ratio and appropriate process, magnetic properties can be controlled to obtain soft magnetic materials such as high magnetic permeability, constant magnetic permeability, and moment magnetic. It has high plasticity and is sensitive to stress. It can be used as pulse transformer material, inductor core and functional magnetic material. ⑥ Iron-cobalt alloy. Cobalt content is 27% to 50%. It has high saturation magnetization and low resistivity. It is suitable for manufacturing pole shoes, motor rotors and stators, small transformer cores, etc. ⑦ Soft ferrite. Non-metallic ferromagnetic soft magnetic material. High resistivity (10-2~1010Ω·m), lower saturation magnetization than metal, low price, used as inductor components and transformer components (see ferrite). ⑧ Amorphous soft magnetic alloy. A non-long-range ordered, grain-free alloy, also known as metallic glass, or amorphous metal. It has high magnetic permeability and resistivity, low coercivity, insensitivity to stress, no magnetocrystalline anisotropy caused by crystal structure, and has the characteristics of corrosion resistance and high strength. In addition, its Curie point is much lower than that of crystalline soft magnetic materials, and the power loss is greatly reduced. It is a new type of soft magnetic material being developed and utilized. ⑨ Ultrafine crystal soft magnetic alloy. A soft magnetic material discovered in the 1980s. It is composed of a crystalline phase less than about 50 nanometers and an amorphous grain boundary phase. It has better comprehensive properties than crystalline and amorphous alloys. It has high magnetic permeability, low coercivity, and low iron loss, and it also has high saturation magnetic induction intensity and good stability. The main research is on iron-based ultrafine crystal alloys.

Micro transformers are divided into micro current transformers (including micro current converters) and micro voltage transformers. They are equipment in the power industry and are generally used in various power instruments for measurement and protection. Compared with ordinary transformers, micro transformers have the characteristics of small size (can be as small as a fingernail) and high precision (ordinary transformers have four precision levels of 0.5, 0.5S, 0.2, and 0.2S, and micro transformers can reach 0.1 level). Micro voltage transformer is a current type voltage transformer. The primary circuit is connected in series with a resistor and the secondary circuit is connected in parallel with a resistor. The voltage is converted into current. After the transformer performs current conversion, the primary output current signal is converted into the required voltage through the sampling resistor. Most of the micro voltage transformers are inserted into the circuit board for use.   There is no resistance on the primary side of the micro current transformer (including micro current converter). The ordinary micro current transformer is a transformer with a resistor in parallel on the secondary side, and the output is current. The micro current converter in the micro current transformer is a resistor in parallel on the secondary side, and the output is voltage. Miniature current transformers are divided into two types: multi-turn winding type (inserted into the circuit board) and through-hole type.

When the power system generates zero-sequence grounding current, the zero-sequence current transformer is used in conjunction with the relay protection device or signal to activate the device components to achieve protection or monitoring.   The specific application of zero-sequence current protection can be to install a current transformer (CT) on each of the three-phase lines, or to let the three-phase conductors pass through a zero-sequence CT together, or to install a zero-sequence CT on the neutral line N, and use these CTs to detect the current vector sum of the three phases, that is, the zero-sequence current Io, IA+IB+IC=Io. When the three-phase load connected to the line is completely balanced (no grounding fault, and the leakage current of the line and electrical equipment is not considered), Io=0; when the three-phase load connected to the line is unbalanced, Io=IN, and the zero-sequence current at this time is the unbalanced current IN; when a grounding fault occurs in one phase, a single-phase grounding fault current Id will inevitably be generated. At this time, the zero-sequence current IO=IN+Id detected is the vector sum of the three-phase unbalanced current and the single-phase grounding current.   The installation of the integral transformer should be carried out before laying the cable, and the cable should pass through the transformer during laying.   The split core current transformer is not restricted by whether the cable is laid or not. The specific method is as follows: (1) Remove the connecting pressure plates of the transformer "K1ˊ" and "K2ˊ" (this requirement is not applicable to circular transformers).   (2) Loosen and remove the two hexagon socket bolts on the top of the transformer (loosen and remove the fastening screws on both sides of the circular transformer), and the transformer will be divided into two parts.   (3) Put the transformer on the cable, wipe the contact surface clean, apply a thin layer of anti-rust oil, align the two parts of the transformer, and tighten the hexagon socket bolts (fastening screws on both sides). The two parts of the transformer should be aligned to avoid affecting the performance.   (4) Fix the connecting plate on "K1ˊ" and "K2ˊ" (this requirement is not applicable to circular transformers).   (5) When installing a transformer with an inner hole > 120 mm horizontally, please add a non-magnetic bracket.

High-frequency current transformer is a sensor that can be widely used for partial discharge detection of high-voltage electrical equipment such as transformers, cables, switch cabinets, GIS, generators, PT cabinets, circuit breakers, etc. of various electrical levels. It can be installed on the grounding wire of the cable input bushing/surge capacitor, the cable body or shielding layer grounding wire, the secondary winding of the current transformer in the switchgear, and the neutral wire of the generator and transformer. The technology is in a leading position in China. How does the high-frequency current transformer detect partial discharge signals?   Partial discharge monitoring is now a technical means of diagnosing the insulation condition of equipment that has been widely recognized and adopted internationally. This technology can also be used for routine inspections or on-site inspections of other high-voltage equipment in substations. The large amount of partial discharge data and the complex situation on site make real-time monitoring of it a challenging task.   When partial discharge occurs inside the cable, the high-frequency current will propagate to the earth along the ground wire. Partial discharge detection is achieved by installing a high-frequency current transformer on the ground wire to detect the high-frequency current signal. The high-frequency current transformer uses the Rogowski coil method, with multiple turns of conductive coils wrapped around the annular core material. The high-frequency alternating electromagnetic field caused by the high-frequency current passing through the center of the core will generate an induced voltage on the coil. There is no electrical connection between the measurement circuit of the high-frequency current transformer sensor and the current being measured. It is a non-invasive detection method, and the equipment being measured does not need to be shut down. Product features:   Ultra-wideband, high frequency   The sensor has excellent instantaneous response ability and can be widely used in high-frequency current measurement   The sensor can be directly put on the conductor to be measured for measurement   Good linearity and high accuracy   Openable ring structure design, designed with self-locking device, easy installation, firm and reliable   Measurement requires destruction of the conductor, open circuit is dangerous   Magnetic shell, internal epoxy resin one-time casting and potting   Protection level reaches IP68, can be used indoors and outdoors all day

1) The wiring of the current transformer should comply with the series connection principle: that is, the primary winding should be connected in series with the measured circuit, and the secondary winding should be connected in series with all instrument loads   2) According to the size of the measured current, select the appropriate change, otherwise the error will increase. At the same time, one end of the secondary side must be grounded to prevent the high voltage of the primary side from entering the low voltage side of the secondary side once the insulation is damaged, causing personal and equipment accidents   3) The secondary side is not allowed to be open. Once the circuit is open, the primary side current I1 will all become magnetizing current, causing a sudden increase in φm and E2, causing the core to be over-saturated and magnetized, causing severe heat and even burning the coil; at the same time, the magnetic circuit is over-saturated and magnetized, which increases the error. When the current transformer is working normally, the secondary side is similar to a short circuit. If it is suddenly opened, the excitation electromotive force will suddenly change from a very small value to a very large value, and the magnetic flux in the core will present a severely saturated flat-top wave. Therefore, the secondary winding will induce a very high peak wave when the magnetic field passes through zero, and its value can reach thousands or even tens of thousands of volts, endangering the safety of the staff and the insulation performance of the instrument. In addition, the primary side open circuit makes the secondary side voltage reach several hundred volts, which will cause electric shock accidents once touched. Therefore, the secondary side of the current transformer is equipped with a short-circuit switch to prevent the primary side from opening. During use, once the secondary side opens, the circuit load should be removed immediately, and then the vehicle should be stopped for processing. It can be used again after everything is handled.   4) In order to meet the needs of measuring instruments, relay protection, circuit breaker failure judgment and fault filtering devices, current transformers with 2 to 8 secondary windings are installed in the generator, transformer, outgoing line, busbar section circuit breaker, busbar circuit breaker, bypass circuit breaker and other circuits. For large current grounding systems, it is generally configured in three phases; for small current grounding systems, it is configured in two or three phases according to specific requirements   5) The installation location of the protective current transformer should be set to eliminate the non-protected area of ​​the main protection device as much as possible. For example: if there are two sets of current transformers, and the location allows, they should be installed on both sides of the circuit breaker so that the circuit breaker is within the cross protection range   6) In order to prevent the flashover of the pillar current transformer bushing from causing busbar failure, the current transformer is usually arranged on the outgoing line or transformer side of the circuit breaker 7) In order to reduce the damage caused by internal faults of the generator, the current transformer used for automatic adjustment of the excitation device should be arranged on the outgoing line side of the generator stator winding. In order to facilitate analysis and detect internal faults before the generator is connected to the system, the current transformer used for measuring instruments should be installed on the neutral point side of the generator.

The protective current transformer is generally used for the relay protection circuit of multiple busbars. It is developed for the protection system to detect short-circuit faults. It has different accuracy levels and accuracy limit coefficients, can be expanded to different perforation sizes, and is widely used in low-voltage distribution protection systems. It can also be used to collect low-voltage overload and short-circuit signals and is used in conjunction with protection relays.   Product advantages   Novel structure, beautiful appearance, easy installation, small size, light weight, high accuracy and large capacity.   Structural features   The shell is made of flame-retardant, temperature-resistant 140°C imported polycarbonate injection molding, the core is made of oriented cold-rolled silicon steel strip, and the secondary wire is made of high-strength electromagnetic enameled wire.   The working principle of the current transformer is shown in Figure 1. The primary winding of the current transformer is connected in series in the measured line. I1 is the line current, that is, the primary current of the current transformer, N1 is the primary number of turns of the current transformer, I2 is the secondary current of the current transformer (usually 5A, 1A), N2 is the secondary number of turns of the current transformer, and Z2e is the impedance of the secondary circuit equipment and connecting wires. When the primary current flows in from the P1 terminal of the current transformer and out from the P2 terminal, when the secondary Z2e is connected, the current I2 flows from S1 through the secondary winding of the current transformer, through Z2e to S2, forming a closed loop due to the principle of electromagnetic induction. It can be obtained that the current is I1×N1=I2×N2 in an ideal state, so I1/I2=N2/N1=K, where K is the transformation ratio of the current transformer.

Precision current transformers are used in many fields. Here are some of the main application areas:   Research units: In the field of scientific research, precision current transformers are widely used in various research projects, such as power engineering, physical research, automation, etc.   Laboratory: In various laboratories, such as power laboratories, electromagnetic laboratories, etc., precision current measurement and control are required, and precision current transformers have become essential equipment.   Manufacturing plants: In manufacturing plants, especially in the production of power equipment and electronic products, it is necessary to accurately control the current to ensure the quality and stability of the product. Precision current transformers play an important role in this process.   Current value transfer: In the power transmission and distribution system, the current needs to be accurately measured and controlled to achieve efficient transmission and distribution of power. Precision current transformers play a key role in this process.   Standard transformers: Precision current transformers are also used as standard transformers to calibrate other current measurement devices to ensure their accuracy.   As mentioned above, the application areas of precision current transformers are not limited to these. It is also widely used in many other power systems and equipment.  

Current transformers based on Permalloy cores have the advantages of high sensitivity and low hysteresis losses, making them ideal for use in wide-range applications. There are several key aspects to consider when implementing a wide-range current transformer:   1. Core material selection   The high permeability and low losses of Permalloy cores make them very sensitive when measuring smaller currents. However, for large current measurements, it is also necessary to ensure that the core is not saturated, so the appropriate core size and shape need to be selected.   2. Core size and shape   Selecting the appropriate core size and shape ensures that current can be effectively measured over the entire range. Larger cores can handle larger currents, but core saturation should be avoided.   3. Multi-level transformer design   To achieve a wide range, a multi-level transformer can be designed, that is, multiple windings are integrated in one transformer, each for a different current range. The different current ranges can be accommodated by electronic switching or paralleling multiple windings.   4. Compensation circuit   The use of compensation circuits can improve the linearity and accuracy of the transformer over a wide range. For example, operational amplifiers can be used for signal conditioning to reduce nonlinear errors.   5. Digital signal processing   Combined with digital signal processing technology, the measurement accuracy and dynamic range of the transformer can be further improved by filtering, amplifying and correcting the measurement signal.   6. Calibration and testing   Regularly calibrate the transformer to ensure its accuracy and stability over the entire range. Use standard calibration equipment and methods to verify and adjust the performance of the transformer.   Implementation example   The following are the design steps for a wide-range current transformer based on a Permalloy core:   1. Select the core: Select a Permalloy core with high magnetic permeability and suitable for wide-range applications. For example, use a C-type or toroidal core with a suitable cross-sectional area and length.   2. Design the primary and secondary windings: Design the primary and secondary windings according to the expected current range. Ensure that the secondary winding can effectively sense the flux changes of the primary winding.   3. Multi-level winding design: Integrate multiple secondary windings in the transformer, each corresponding to a different current range. Use an electronic switch or multiplexer to select the appropriate winding.   4. Signal conditioning circuit: Design a signal conditioning circuit, use operational amplifiers and filters to process the sensing signal, and improve the linearity and signal-to-noise ratio of the signal.   5. Digital processing module: Combined with a microcontroller or digital signal processor, the conditioned signal is sampled, processed and corrected. Automatic range switching and digital output can be achieved.   6. Calibration and testing: Use a standard current source to calibrate the transformer to ensure its accuracy throughout the range. Verify the effectiveness of the design through experimental tests, and adjust and optimize it according to the test results.   Through the above steps, a wide-range current transformer based on Permalloy core can be designed and implemented, which is suitable for various current measurement applications with high precision and wide dynamic range.