电桥法测定电缆三相绝缘故障的新方法

Novel Method for Locating Insulation Failure of Three phase Cables by Bridge Circuit

在电缆三相同时发生绝缘故障时，用电桥法定位将产生较大误差。本文通过理论分析导得一校正公式：ｌｃｘ＝（ｋ＋１／ｋ－１）ｌｍｘ－２ｌ／（ｋ－１），其中ｋ为近似完好相与故障相绝缘电阻比，ｌ为电缆的全长，ｌｍｘ为故障位置的测量值，ｌｃｘ为ｌｍｘ的校正值。实验表明，如ｋ＞２，经校正的定位误差将小于±１％，其准确度能完全满足工程测量的要求。

If insulation failures exist in all three phase of a cable,the failure point locating error caused by bridge circuit will be large.By means of theoretical analysis,a corrective formula is deduced in this paper:l c x=k+1k-1l m x-2lk-1,where k is the insulation resistance ratio of the approximate normal phase to the fault phase, l is the cable's total length, l m x is the measured value of the failure point location, l c x is the corretive value of l m x .Experiments indicate that if k>2 ,the corrective locating error is less than ±1%,which is accurate enough for engineering application.