1、Transformer inrush current suppression Transformer inrush current leads not only to the protective relaying misoperation, derived from the power grid voltage sags, harmonic pollution, and the inrush current, ferromagnetic resonance overvoltage in power system operation, to bring the negative effect
2、that cannot underestimate. For decades the people through the identification of inrush current feature method to reduce the relay misoperation rate, but did not gain a good return, malfunction rate is still high. As for the voltage sag, harmonic pollution, and the inrush current, elimination of the
3、more be nonplussed over sth. The reason is that people think the inrush current appears irresistible, can only use recognition countermeasure, namely hide countermeasure. In fact, change a train of thought - inhibition, can be fully realized, and have achieved. Introduction Transformer inrush and su
4、rge suppression capacitor chargingprinciple is completely similar to the inductance and capacitance are energy storage devices, the former does not allow current mutation, which does not allow voltage surge,power drop will induce a transient process. Access in the power transformer no-load transform
5、er outlet power failure andprotection devices to be removed, because of a side of the transformer windings to feel the surge applied voltage values are sometimes generated a great inrush current. Inrush currentpeak is not only large, and contains very many harmonics andDC component. Electrical equip
6、ment on the grid and thusresult in an extremely negative impact. 1. the danger of inrush current 1.1 caused by the transformer protection devices malfunction,the frequent failure of the transformer and put into operation;1.2 removal of the transformer short-circuit fault outlet voltage generated whe
7、n the sudden increase in the protection induced by transformermalfunction, so that each side of the transformer load all thepower;1.3 A power station access to a power transformer no-load inrush current generated, inducing other B power station nearby, C power station transformers are running a and
8、should surge (sympathetic inrush) and false tripping, resulting in a large area power failure; large inrush currentvalue of 1.4 would result in electric power transformers andcircuit breakers due to excessive damage; 1.5-induced over-voltage, damaged electrical equipment; 1.6 inrush current of the D
9、C component lead to over-current transformermagnetization and magnetic significantly reduce themeasurement accuracy and the correct action rate ofprotection devices; 1.7 magnetizing inrush current in a large number of harmonics on power quality caused by pollution.1.8 caused by voltage sags or swell
10、s, affecting the normal operation of other electrical equipment. For decades, people have taken to the inrush current approach is to hide, but because of inrush current form and characteristics ofdiversity, through mathematical or physical methods toidentify its characteristics difficult to improve
11、the accuracy ofthat inrush current in this field has been a historical problem. 2. the magnetizing inrush currentcauses Suppressor is an important feature of the strategy adopted bymagnetizing inrush current is not escape, but suppression. Inrush current theory and practice that can suppress or even
12、 eliminate, because the source of inrush current is generated in the transformer windings on either side felt the applied voltage increases, based on fluxconservation theorem, the windings in the magnetic circuit will produce a single polarity of the magnetic bias, such as partial pole and transform
13、er of exactly the same as the original remanence polarity, it may bias magnetic remanence andsteady-state flux superimposed with the result of magnetic saturation, thus greatly reducing the magnetizing reactance ofthe transformer windings , and then induced a significantinrush current value. As the
14、partial magnetic polarity and the value is applied voltage switch by selecting the phase angle control, and therefore, if we can grasp the power transformer when the last of remanent magnetic polarity, they can drop by when the control transformer the supply voltage phase angle, which allows magneti
15、c bias with opposite polarity remanence, which eliminate the inrush current of the soil -magnetic saturation, to achieve the inrush current . For a long time, people found it impossible to measure thetransformer polarity and remanence values, and thus had to abandon the use of the idea of partial re
16、manence magneticoffset. Inrush current in response to the strategy does notappear on the two smooth road, a road through the control power transformer voltage drop closing phase angle, so that it does not produce magnetic bias, in order to avoid magnetic saturation occurs when the power drops . The
17、other way is the use of physical or mathematical method foridentifying the characteristics of magnetizing inrush current, in order to lock in the power transformer protection devices drop, that the aforementioned avoid strategy. The two fatal road has its problems, capture does not produce magnetic
18、bias voltage closing angle of only two, namely, the two sinusoidal voltage peak point (90 or 270 ), if you deviate from these two points, partial there will be magnetic, which requires control of the closing part of all institutions (including circuit breakers) should be accurate, stable operating t
19、ime,because, as 1 millisecond time drift action, closing phaseangle of 18 will produce the error. In addition, three-phase voltage of the peak is not at the same time coming, but the difference between 120 , to completely eliminate the three-phase inrush current, must be time-phase three-phase circu
20、it breaker closing can be achieved, and the current operating rules prohibit such power will be lead to time-sharing-phasesplit-phase operation running, not to mention some circuit breakers in the sub-phase structure can not operate. dentification with the physical and mathematical methods of magnet
21、izing inrush current rather difficult, because the characteristics of magnetizing inrush current and a lot of factors, such as closing phase angle, the electromagnetic parameters of the transformer and so on. A large number of scholars and engineers through decades of unremitting effortsstill can no
22、t find an effective way, because of its high degree of difficulty, that is to avoid strategy difficult, the Achilles heel ofthis strategy is to tolerate the other excitation inrush current occurs, the pollution of its power grid and electrical equipment,there is still destructive. Transformer diagra
23、m 2-1 Figure 2-1 is a single-phase transformer structure, we can write the no-load voltage of the primary winding of the equation Where N1, R1, respectively, for the primary winding turns and the resistance （2.2)(2.1) can be rewritten as Where t = 0, U1, such as ignoring the initial phase angleresis
24、tor R1, which Let R1 = 0, we obtain the solution (2.3)-type equations have an expression for the magnetic flux Based on flux conservation theorem, in the closing momentsmagnetic flux can not change suddenly, you can find theintegration constant C. The amplitude of the total flux from equation (2.6)
25、is not difficult to see that the applied voltage transformer u1 in the early phase angle different when closing the magnetic fluxgenerated by is not the same, the equation (2.6) is rewritten as(2.7) for the transient flux, that is, magnetic bias, in the closing moments p value of for the 90 or 270 d
26、rop at p = 0, at 0 or 180 when dropped up to the peak m p . Equation (2.7) in for the steady-state flux, as a periodic function. Figure 2-2 for the drop-closing angle = 0, the flux curve, the steady-state flux diagram s, is s and p total flux synthetic (not taking into account the remanence res), sa
27、t for the transformer saturation flux. For the lossless transformer (R1 = 0) magnetic bias p will not decay, the solid line shows, for lossy transformer (R1 0) Closing angle = 0, the flux curve of Figure 2-2 Dashed line. As can be seen from Figure 2-3 in the voltage phase angle range 1 to 2 greater
28、than the total flux saturation flux sat, magnetic saturation, resulting inrush current iy, iy has a discontinuity. For the lossless transformer and iy is about even symmetry of the waveform, while the discontinuity in theiy = 0 is the angular range of the even symmetric waveform. For and iy is detri
29、mental tothe transformer will no longer symmetrical relationship. When taking into account the remanence, the remanence will be the total magnetic flux, magnetic bias (transient flux) andsteady-state flux of the three components. Difficult to see inFigure 2-2 Bias in the case, such as remanence is p
30、ositive, the total flux curve upward shift, that more saturated magnetic circuit, inrush current amplitude will be greater. If remanence is negative, the inrush current is suppressed. Core material hysteresis loop in Figure 2-3 、 Figure 2-2 is the hysteresis loops of ferromagnetic materials,which de
31、scribes the excitation coil in the magnetic circuit on the AC voltage applied, the corresponding magnetic potential H-Hc to Hc from between the change in magnetic flux generated by H (or magnetic flux density B = / S) in the corresponding hysteresis loop changes. If the H line at some point suddenly
32、 back to zero, then B will then fall into the B-axiscorresponds to a certain point, the point corresponding to theB value is the remanence Br. Remanence values can be seenwith the removal of excitation voltage and polarity of the phaseangle, and if in the first , excitation power off quadrant (ie,H
33、= 0) then the remanence is positive or zero, in , quadrant cut off the excitation power, the remanence is negative.3.the magnetizing inrush current suppression method Transformer energized during normal working hours, the main magnetic flux in the applied voltage waveform and the waveform is basical
34、ly the same, that is a sine wave. Magnetic flux lags the supply voltage of 90 , by monitoring the supply voltage waveform to achieve the flux waveform monitoring,then get off when the supply voltage polarity remanence. Dropon the power transformer magnetic bias p also generatedas a result of magneti
35、c bias, the power supply voltage when the initial phase angle in , quadrant bias generated within the range of magnetic polarity is positive, while the initial phase angle in , quadrant bias generated within the range of magnetic polarity is negative. Clearly, the remanence polarity shows that the m
36、agnetic polarity bias control, so long as the power drop and remanence magneticpolarity opposite side, he incurs surge suppression. Figure 3-1for the transformer primary voltage u, the main magnetic flux , and the bias magnetic remanence Res p with sub-gate the relationship between the angle and clo
37、sing angle curve, and the sub-gate supply voltage u beginning ofthe phase angle with the remanence Res curve. The main transformer in the steady state flux lag the supply voltage u 90 , tTransformer no-load power generated when the magnetic bias must correspond with the steady state voltage u at pow
38、er point on the curve of steady-state flux power equal,opposite polarity, The maximumsteady-state flux up to the peak m, while the amplitude of magnetic remanence Res material characteristics. Easy to see the early phase corresponds to the same angle or closing the sub-gate initial phase angle and t
39、he resulting magnetic remanence of the very partial.Transformer primary voltage u, the main magnetic flux , and the bias magnetic remanence Res p with sub-gate the relationship between the angle and closing angle curve of the opposite, that is measured by the sub-gate sub-gate voltage angle , and pr
40、eserved, the selection of the transformer in the next drop in the closing angle equal to , when coupled with power, and bias magnetic remanence can reverse, theywill be less than the synthesis of magnetic flux saturation flux sat .(Due to saturation flux is generally larger than the steady-state flu
41、x peak selection), the magnetic circuit is not saturated, in order to achieve inrush current suppression. As the three-phase three-phase supply voltage of the circuit breaker when the linkage has been cut three-phase sub-phase of thedifference between the gate 120 , the phase difference between the
42、remanence polarity is 120 , and when closing the three-phase three-phase co-linkage initial phase angledifference between the gate is 120 , the phase difference between the partial pole is also 120 , so that the naturalrealization of the three-phase transformer magnetic circuitbias magnetic and rema
43、nence are offset to avoid a circuit breaker must be with a time share in order to suppress inrush current demanding, that support for three-phase three-phasecircuit breaker linkage surge suppression. As long as the partial inhibition of inrush current and remanent magnetic polarity opposite to, are
44、not required to fully offset,so when the closing angle relative to a greater angle of the previous sub-gate bias, as long as no magnetic bias and remanence are added together, the magnetic circuit not saturated, which greatly reduces the operating time of circuit breaker operating mechanism precisio
45、n requirements for the practical application of this technology laid the foundation.Suppressor and fast cutting of such devices and equipmentcan be realized from the investment unit linked by cold stand by spare transformer run, which will greatly reduce no-load transformer hot standby mode energy c
46、onsumption.Figure 3-3presents selected four inrush current Iy and thesub-gate angle and the closing angle of the curve, you can see, in the closing angle of 90 or 270 , drop the transformer inrush current and transformer before sub-sub-gate angle has nothing to do, because the transformer primary vo
47、ltage over peak power does not produce magnetic bias, regardless of whether the original transformer magnetic saturation remanence will not. Of course, if you use three-phase circuit breaker is not possible linkage phase of themagnetic bias is zero. And when the closing angle is 0 or180 when the dro
48、p the transformer inrush current and the previous sub-gate angle is closely related to, when and are similar (about a difference of 60 ) when the inrush current is suppressed, then and the greater the deviation,the greater the inrush current. It can be seen as closing the circuit breaker when the time shift at 3ms surge suppression for no influence. Todays vacuum circuit breakers and SF6 circuit breaker, closing time drift are within1ms, can accurately achieve the inrush current suppression. Tripping angle and closing angle of the inrush cur
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