Permalloy annular cut core

Motor energy saving and core material development Today, it can be said that more than half of the total global electricity consumption comes from motors. High-efficiency motors are urgently needed to control carbon dioxide emissions and thereby curb global climate warming. The key to achieving this high-efficiency motor is the core material. The core material of the motor, as the name implies, is made of iron-containing materials. The core material is made of magnets and plays an important role in controlling the magnetic flux of the motor (forming a magnetic field), but it also becomes a source of heat due to iron losses (hysteresis loss and eddy current loss). So, will it be possible to achieve high efficiency of the motor by choosing a core material with small iron loss? Not so. Core materials have many properties. Moreover, even the same core material has different required properties when used in motors and when used in transformers. In recently developed high-efficiency motors, amorphous alloys are used instead of non-oriented electromagnetic steel sheets as core materials, and combined with ferrite magnets, ultra-high efficiencies previously thought to be impossible have been achieved. This article will explain the selection and use of motor core materials based on this case.   Core materials can be divided into two categories   Core materials are also called soft magnetic materials. Figure 1 shows the main soft magnetic materials.   What kind of motor core material is better? If there is no heating effect of iron loss, using soft magnetic materials with large Bs in the core can obtain the maximum magnetic flux density Bm of the core. In addition, the volume of the core is inversely proportional to the square of Bm. From the perspective of miniaturization, materials with large Bs also have advantages. On the other hand, from the perspective of improving efficiency, soft magnetic material cores with small iron losses are preferred. Therefore, high-quality soft magnetic materials with high Bs and low iron loss located in the lower right area of Figure 2 are needed. However, as shown in Figure 2, there is a compromise between high Bs and low iron loss, and the ideal soft magnetic material that can satisfy both does not exist. It can also be seen from Figure 2 that when the frequency is 1kHz, in terms of high Bs, Perminde alloy has advantages; in terms of low iron loss, nanocrystalline soft magnetic alloy and PC-type permalloy (high magnetic permeability material) are more advantageous. Advantage.   Comparing iron-based amorphous materials and non-oriented electrical steel sheets Comparison of the initial magnetization curves of iron-based amorphous alloy SA1 and non-oriented electromagnetic steel plate 35H300 is shown in Figure 3. For SA1, in order to relax the stress exerted on the alloy during casting, the magnetic properties can be improved through magnetic field-free heat treatment in a nitrogen atmosphere. However, since SA1 will become embrittled under heat treatment, heat treatment is mostly not performed when used in motors. When it exceeds B-0.8T, the magnetizing field strength of SA1 becomes greater than that of 35H300 (the magnetic permeability becomes smaller).   Evaluate core processing Figure 4 shows the iron loss comparison between SA1 and 35H300 slotted and cut cores without heat treatment. In the case of 400Hz and B.=1.0T, the iron loss of the SA1 core is 2Wkg and the iron loss of the 35H300 core is 20Wkg. The former is 1/10 of the latter. Based on this, it is extremely effective in improving the efficiency of motors, such as in battery-driven motors, and has the effect of extending battery life. In addition, the higher the driving frequency, the greater the iron loss difference between the two. This situation also applies to high-speed motors. Figure 5 shows the structure of an 11kW double-rotor axial gap motor, which uses an SA1 stator core and a ferrite sintered magnet rotor. The stator core is a simple structure in which amorphous alloy SA1 is cut into long strips, laminated, and fixed with resin. It is a slit-cut core. The stator core is made of non-oriented electromagnetic steel plates of the same shape, which are cut into long strips and then laminated and fixed with resin to obtain another motor. The loss comparison between it and the motor shown in Figure 5 is shown in Figure 6. Compared with the 35H300 stator core, the SA1 stator core can reduce the iron loss by 1/5. In addition, by reducing the excitation current, the copper loss can be reduced by about 15%, reaching an efficiency of 93.2% in line with the IE4 standard. Furthermore, on the basis of this motor, the characteristics of amorphous alloy are fully utilized, which is smaller than the traditional three-phase induction motor. A high-efficiency motor that meets the IE5 standard is being developed.   Read more:  https://www.hemeielectricpower.com/

Why can't the current transformer be opened when it is running? What is the principle? What are the adverse effects of opening a circuit?   Most welders often hear this sentence: "The secondary side of the current transformer cannot be open-circuited, and the secondary side of the voltage transformer cannot be short-circuited." At work, everyone must regard this as the "Quran". When disassembling the secondary line of the current transformer, first add a short rotor or short wiring to connect the secondary side, and then perform surgical removal or wiring work. , Only in this way can the safety of the person be guaranteed, which is a very appropriate approach. When I removed the current wire of the electric meter before, I encountered a situation where the wiring was not firm and the terminals were crackling with charge and discharge. So why can't the secondary current transformer be open circuited? What is the principle? What adverse effects will it cause? The following is a detailed analysis for everyone, I hope everyone can understand it. When the current transformer is working normally, the load connected to the secondary coil is an ammeter or meter current coil and a smart transmitter, etc. The impedance of these coils is not large, and most of them operate in short circuit conditions. Fault conditions. In this case, the magnetic flux generated by the primary current of the current transformer and the secondary coil current cancel each other, keeping the magnetic flux density in the core at a moderate level, usually at a few tenths of a Tesla ( The unit of magnetic flux density: T), because the secondary coil resistor is not large, the operating voltage of the secondary coil is also very low. Under normal operating conditions, the magnetic fluxes of current transformers cancel each other, and the relative density of the magnetic fluxes is not large. When the secondary winding of the current transformer is open-circuited, if the primary current does not change, the secondary circuit is broken, or the resistor is very large, then the current on the secondary side is 0, or very small, and the secondary coil Or the magnetic flux of the iron core is not large and cannot offset the primary magnetic flux. At this time, all the primary current turns into self-induced electromotive force, saturating the iron core. This change is sudden, called a sudden change, and its magnetic flux density reaches several Teslas.   Adverse effects of secondary open circuit of current transformer   When this kind of situation occurs, it will cause the following adverse effects:   1. The second generation of thousands of volts of voltage (this has not been certified, it is a copied theory), the high voltage will penetrate the insulation layer of the current transformer, causing the entire substation equipment casing to be induced and electrified, and will also It will cause electric shock accidents to maintenance workers and threaten their lives.   2. A sudden change in the saturation state of the iron core will increase the core loss of the voltage transformer, and the iron core will become hot and damage the voltage transformer.   3. The saturated iron core of the voltage transformer is in a saturated state, the measurement calibration is inaccurate, and the CT ratio difference and angle difference increase. 

1. Principle of power acquisition by collection unit The fault indicator acquisition unit uses the electromagnetic induction principle of "moving electricity generates magnetism, and moving magnet generates electricity" to generate electricity on the secondary coil through the electromagnetic coupling of the permalloy core. Voltage and current realize the transmission of electric power and achieve the purpose of drawing electricity from the conductor. As shown in the figure, when a primary current flows through the primary winding N1, an alternating magnetic flux Φ1 is generated in the core magnet. This alternating magnetic flux Φ1 passes through the core magnetic circuit and generates an induced voltage value U on the secondary winding. Compared with other electromagnetic mutual inductance transformations, the primary winding here is a cable or wire, and the number of turns is 1 turn. When the alternating magnetic flux Φ1 forms a closed loop in the magnetic core, it will be hindered by magnetic resistance Φr, magnetic space radiation (magnetic leakage ΦL), etc. Part of the magnetic flux will be lost, and only this part of the magnetic flux that passes through the secondary winding Φ2 can effectively transfer electric energy to the secondary side, that is, Φ1=ΦL+Φr+Φ2. It can be seen that under the same working conditions, the smaller the reluctance Φr and magnetic leakage ΦL, the greater the power output by the secondary side will be. Since the permalloy magnetic core acquisition unit needs to meet the requirements of live installation and disassembly, the magnetic core needs to adopt the cutting and snapping mode, that is, the magnetic core needs to be cut into two halves during production and then closed to form a ring magnetic circuit during installation. When the magnetic circuit is closed, an air gap will be generated due to the cutting gap. Compared with the original annular core, its magnetic resistance Φr and magnetic leakage ΦL are greatly increased. Under the same working conditions, the better the cutting process, the smaller the air gap, and the smaller the magnetic resistance. The smaller the resistance Φr and magnetic leakage ΦL will be, the greater the secondary side output power will be. In order to reduce the magnetic circuit loss and increase the secondary side output power level under the same wire current, it is necessary to use magnetic core materials with high magnetic permeability and high saturation magnetic flux density Bs value, making the selection of magnetic core materials tend to be high-end. . After our many experiments, the materials that meet the power extraction requirements of the fault indicator collection unit are: permalloy 1J85, iron-based nanocrystal 1K107.   Physical Properties/Magnetic Properties of Magnetic Materials: 2. The relationship between magnetic flux and power/correlation calculation between theoretical formulas: (1)Φ1=B*Ae (2)B=μ*H (3)μ=AL*Le/0.4*π* N²*Ae(N²=1) (4) H=0.40π*N*I/Le in: μ: magnetic permeability B: Magnetic flux density Ae: core cross-sectional area H: magnetic field strength AL: inductance coefficient Le: equivalent magnetic circuit length It can be seen that at the same primary side current, the higher the magnetic permeability μ, the shorter the equivalent magnetic path length Le of the magnetic core, the larger the core cross-sectional area Ae, and the larger the primary side magnetic flux Φ1.   In order to minimize the losses of Φr and ΦL after the magnetic flux on the primary side is transferred to the secondary side, it is necessary to reduce the reluctance loss and magnetic leakage loss, that is, to increase the magnetic permeability, optimize the effective magnetic path length of the magnetic core, and adopt excellent technology to ensure The cut surfaces of the core fit snugly. In our actual processing practice, the magnetic permeability of 1K107 iron-based nanocrystalline magnetic core after cutting can reach more than 15,000, and the magnetic permeability of 1J85 permalloy magnetic core after cutting can reach more than 12,000. What is the magnetic permeability of permalloy core after cutting? To be broken down in the next episode.   3. Analysis of the reasons for burnt power coil Since the power coil works under power frequency conditions, if the magnetic core is properly designed, the iron loss caused by the eddy current in the magnetic core will not be too large, so the permalloy magnetic core will not burn out. The situation is mainly caused by improper design of the secondary winding. When the operating current on the primary side of the fault indicator rises, the output current on the secondary side will also rise accordingly, that is, I1:I2 =N1:N2 is satisfied. Therefore, it is necessary to consider the winding copper wire according to the possible continuous maximum current on the primary side conductor. The wire diameter and current density on the winding should not be too large, otherwise high heat will be generated on the winding, causing the coil to burn out.   4. Example application 1J85 (0.2mm permalloy) and 1K107 (0.025mm iron-based nanocrystal) are both ultra-high permeability soft magnetic materials. Under power frequency conditions, the eddy current loss is almost negligible. In the current fault indicator acquisition unit In power applications, its excellent magnetic properties are unmatched by other permalloy core magnetic materials. The price of magnetic cores between 1J85 and 1K107 is about 2:1. In large-volume applications, 1K107 has outstanding magnetic performance advantages and price advantages.

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.