【文章內(nèi)容簡介】 exactly the same as the original remanence polarity, it may bias magic remanence andsteadystate flux superimposed with the result of magic saturation, thus greatly reducing the magizing reactance ofthe transformer windings , and then induced a significantinrush current value. As the partial magic 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 magic polarity, they can drop by when the control transformer the supply voltage phase angle, which allows magic bias with opposite polarity remanence, which eliminate the inrush current of the soil magic 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 remanence magicoffset. 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 magic bias, in order to avoid magic saturation occurs when the power drops . The other way is the use of physical or mathematical method foridentifying the characteristics of magizing 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 magic bias voltage closing angle of only two, namely, the two sinusoidal voltage peak point (90 176。 or 270 176。), if you deviate from these two points, partial there will be magic, which requires control of the closing part of all institutions (including circuit breakers) should be accurate, stable operating time,because, as 1 millisecond time drift action, closing phaseangle of 18 176。 will produce the error. In addition, threephase voltage of the peak is not at the same time ing, but the difference between 120 176。, to pletely eliminate the threephase inrush current, must be timephase threephase circuit breaker closing can be achieved, and the current operating rules prohibit such power will be lead to timesharingphasesplitphase operation running, not to mention some circuit breakers in the subphase structure can not operate. dentification with the physical and mathematical methods of magizing inrush current rather difficult, because the characteristics of magizing inrush current and a lot of factors, such as closing phase angle, the electromagic parameters of the transformer and so on. A large number of scholars and engineers through decades of unremitting effortsstill can not 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 diagram 21 Figure 21 is a singlephase transformer structure, we can write the noload voltage of the primary winding of the equation Where N1, R1, respectively, for the primary winding turns and the resistance （ ) () can be rewritten as Where α t = 0, U1, such as ignoring the initial phase angleresistor R1, which Let R1 = 0, we obtain the solution ()type equations have an expression for the magic flux Φ Based on flux conservation theorem, in the closing momentsmagic flux can not change suddenly, you can find theintegration constant C. The amplitude of the total flux from equation () is not difficult to see that the applied voltage transformer u1 in the early phase angle α different when closing the magic fluxgenerated by Φ is not the same, the equation () is rewritten as () for the transient flux, that is, magic bias, in the closing moments Φp value of α for the 90 176。 or 270 176。 drop at Φp = 0, at 0 176。 or 180 176。 when dropped up to the peak Φm Φp . Equation () in for the steadystate flux, as a periodic function. Figure 22 for the dropclosing angle α = 0, the flux curve, the steadystate flux diagram Φs, Φ is Φs