减少Kerr效应法在油纸绝缘结构中直流电场测量误差的方法

Methods to Decrease the Measuring Errors of DC Electric Field Measurement in the Oil-paper Insulation Based on the Kerr Effects

Kerr效应法是液体电介质中电场测量的有效方法,但利用该方法在油纸复合绝缘结构中的直流电场准确测量一直是电介质中电场测量的难点。为此,基于Kerr效应法搭建了一套在线非接触式的液体电介质中光学电场测量系统,分析了引起测量系统误差的主要原因,提出了减小测量误差的方法。通过加长电极和边缘绝缘包覆处理,可将电极边缘效应相对误差减小至1.3%;通过光学器件光学特性的标定,修正了器件非理想因素的误差;通过对激光器噪声的统计分析,合理选取了交流调制电源的频率,提高了测量系统的信噪比,可将激光管同频噪声干扰所导致的直流电场测量相对误差减小到0.86%,交流电场测量相对误差减小到1.6%。经过试验测定,整个测量系统直流电场强度测量灵敏度可达到20V/mm,总体相对误差<5.4%。

The Kerr electric-optic effects could be useful for measuring electric field in liquid dielectric;however,it is difficult to apply them to accurately measure electric field in oil-paper insulation system.Thus,we established a contact-free on-line electric field measurement platform for measuring electric field in liquid dielectric based on the Kerr electric-optic effects.Based on the platform,factors leading to its measurement errors and measures to reduce these errors were analyzed and discussed.It is concluded that relative errors caused by edge effect of electrode and pressboard can be reduced to 1.3% by lengthening the electrode and covering it by oil-impregnated paper.Moreover,the actual parameters of the optical components were measured to correct the errors caused by the non-ideal characters of the optical components.In order to increase the signal noise ratio of the system,the frequency of AC modulated voltage applied to the testing model was carefully selected based on a statistical analysis of the frequency spectrum of the laser output noise by FFT,and then the relative errors caused by the source noise could be reduced to 0.86% for DC electric field measurement,and 1.6% for AC electric field measurement.At last,a sensitivity test of the measurement platform was performed with a plate electrode,indicating that the system was capable of measuring DC fields with accuracy of 20 V/mm and a relative error lower than 5.4%.