低压电器短路试验功率因数的三极值点测量法

Three extreme point measuring method for low voltage electrical short circuit test

针对低压电器短路耐受强度试验中,短时大电流试验条件下测量功率因数一直没有简便而准确方法的问题,该文通过理论分析短路电流波形特性,得出试验回路时间常数与短路电流波形前3个半波电流极值点之间的时间差具有唯一对应关系,从而提出一种全新的功率因数测量方法——三极值点法,该方法不依赖于电压测量值或电流测量值大小,不需要特定的试验设备或测量设备,只需要测量短路电流波形前3个半波极值点之间的时间差和周期分量的频率,带入非线性方程中,通过求解非线性方程即可准确计算出功率因数。结合理论分析和仿真验证,表明三极值点法可简单准确地测量短路试验中的功率因数。

In the short-circuit withstand test of low voltage electrical apparatus,there has not been a simple,exact method to measure power factor under the condition of short time large current test.By theoretically analyzing the characteristic of short circuit current waveform,this paper concludes that time constant of test loop correlates well with the time difference between the first three half-wave current extreme points in the short circuit current waveform,and then presents a new power factor measurement method called three extreme point method.This method neither depends on measurement value of voltage or current measurement value nor depends on a specific test equipment or measuring equipment.It only needs to measure either the time difference among the first three half-wave current extreme points or the frequency of the periodic component.Then,in a non-linear equation,the power factor can be accurately calculated by solving the nonlinear equation.Through theoretical analysis and simulation verification,it is proved that this method is easy and effective to measure the power factor in a short circuit test.