Oriented silicon steel stacked rivet measuring 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/

In power engineering, current transformers convert large currents into small currents and are used for the protection, measurement and measurement of power systems. Today I will explain to you how to choose a current transformer.   The technical conditions for current transformer selection and verification include: primary circuit voltage, primary circuit current, secondary load, secondary circuit current, accuracy level and transient characteristics, relay protection and measurement requirements, dynamic stability multiple, thermal Stability factor, mechanical load and temperature rise. In addition to the above technical conditions, it should also be calibrated according to the use environment: ambient temperature, maximum wind speed, relative humidity, pollution, altitude, earthquake intensity and system wiring method.   The rated primary voltage of the current transformer should not be less than the rated primary voltage of the circuit, which is generally the nominal voltage of the system instead of the highest working voltage.   The rated primary current of the current transformer is an important and difficult point in the selection. Generally, it can be selected according to the rated current or maximum operating current of the primary equipment to which it belongs. The standard values of the rated primary current are: 10A, 12.5A, 15A, 20A, 25A, 30A, 40A, 50A, 60A, 75A and their decimal multiples or decimals. The primary current of the current transformer winding for measurement and metering should be selected strictly according to the loop operating current. In actual use, the transformation ratio difference on each side of the current transformer connected to the main transformer and busbar differential protection should not be greater than 4 times.   As shown in Figure 1, for each circuit of the 35kV bus of a 50MVA booster station, the rated current of the main transformer circuit is 866A, the outlet circuit is 600A, the reactive power compensation circuit is 300A, and the rated current of the station transformer circuit is 10A. Because the rated current of the station transformer loop is very small, the primary current of the protection level winding of the current transformer of this loop is 1/4 times the current of the main transformer side; the primary current of the main transformer loop is selected as 1000A, and the primary current of the protection level of the station transformer loop is optional. It is 250A. Considering the consistency of the transformer ratio, the primary current of the station transformer circuit protection level can be selected as 300A, and the measurement and measurement is generally selected as 50A.   When the high-voltage side of the main transformer is a directly grounded system, the primary rated current of the neutral point current transformer should be 50% to 100% of the rated current of the high-voltage side of the transformer, and meet the specified error limit. The rated primary current of the discharge gap zero-sequence current transformer of the neutral point complete device should be selected according to 100A.   The cores of the current transformers on each side used for transformer differential protection and differential protection of the same busbar should have the same core form.   For P and PR class current transformers, they are only required to meet steady-state non-saturation, while TP class current transformers are required to be non-saturated throughout the entire working cycle.   The above is the current transformer selection compiled by the editor based on specifications and actual engineering experience. Please also pay attention to the reference in practical applications.   Read more:  https://www.hemeielectricpower.com/

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.