杂散参数对冲击电流波形影响的数学分析

在冲击电流试验回路中,输出波形必须满足IEC标准规定的要求。已有研究表明,杂散参数对陡波冲击电流发生回路的影响尤为严重,而且避雷器等试品具有非线性U-I特性,在冲击电流发生回路的设计中必须考虑。针对此问题,首先研究了回路的剩余电感对输出波形的影响。对于波前时间小于1μs的陡波冲击电流发生器,回路需要的总电感在1μH左右,所以要尽量减小回路的剩余电感,否则会使波前时间增大,超出IEC标准要求。然后在线性回路情况下推导了考虑杂散电容时回路输出电流的表达式,进而研究杂散电容对输出波形的影响。研究表明,随着杂散电容的增大,波前时间和波尾时间增大,回路效率降低。但只要杂散电容小于0.1μF,其对冲击电流波形参数引起的误差都在IEC标准规定的误差容限之内。实际回路杂散电容以pF计,因此可以忽略不计。最后,同时考虑试品的非线性特性和杂散电容,分析了杂散电容对输出波形的影响,结论与在线性回路情况下一致。另外避雷器试品有助于提高波头陡度,这是陡波冲击试验中的有利因素。

Mathematical Analysis on the Effect of Stray Parameters on Impulse Current Waveforms

In the impulse current test circuit,the output waveform must be satisfied with the requirements of IEC standard.The previous investigations have proved that the stray parameters have more serious impacts on the steep front waveform.Due to the nonlinear U-I characteristics of example under test(EUT),such as surge arresters,it must be considered in the designing of impulse current generator circuit.For these problems,firstly,the impact of the residual inductance on the output waveform has been investigated.For the steep wave impact current generator with the waveform front time less than 1μs,the required total inductance in the circuit is about 1μH,so the circuit inductance must be decreased as far as possible.Otherwise,the waveform front time would be increased,which will exceed the IEC standard requirement.Then,in the case of linear circuit,the expression of circuit output current,which take the stray capacitance into account,is deduced,and then the impact of the stray capacitance on the output impulse wave is studied.It is indicated that,the wave front time and the wave tail time increases with the increase of stray capacitance,but the circuit efficiency reduces.As long as the stray capacity is smaller than 0.1μF,the caused error of impulse current waveform parameters is in the permission range of IEC standard.However,in practice,the stray capacitance is in pF,consequently,the stray capacitance can be ignored.Finally,when the nonlinear characteristic of EUT and stray capacitance are both considered,the impact of the stray capacitance on the output impulse wave was investigated.The conclusion is consistence with that in the case of linear circuit.Additionally,the EUT of lightning arresters is in favor of decreasing the wave front time,which is an advantageous factor in the steep wave impulse test.