小电流接地系统单相接地故障选线测距和定位的新技术

按照小电流接地系统单相接地故障的特点，本文提出了通过检测注入信号的路径和特征来实验现选线，测距和定位的“Ｓ注入法”选线，测距和定位新原理，导出了有关的公式和算法，研制了相应的装置，并已在较大范围内推广应用。

A NEW APPROACH OF FAULT LINE IDENTIFICATION,FAULT DISTANCE MEASUREMENT AND FAULT LOCATION FOR SINGLE PHASE-TO-GROUND FAULT IN SMALL CURRENT NEUTRAL GROUNDING SYSTEM

According to the characteristics of small current neutral grounding system and on the basis of a special signal injection method, in this paper a new approach is presented to identify the fault line,measure the fault distance and locate the fault position of single phase-to-ground fault by detecting the path and feature of the injected signal.The main features of the special signal injection method are as follows: (a) A current signal from a special signal generator is injected into the fault phase through a potential transformer (PT) because the fault phase of the PT is temporally in idle state during the period of single phase-to-ground fault. Except the PT no other primary equipment is needed,and no any harmful influence on working equipements will occur. (b) The feature of the injected signal differs from any inherent signals in the power system,and the detection of the signal will not be affected by the operation state of the power system. (c) The injected signal only flows in the faulted phase of the fault line and will not enter into any other parts of the system.Deducing relevant formulae and algorithm, a new type of protection device for single phase-to-ground fault in small current neutral grounding system is developed. About 2000 sets of this protection device are put into use in practical small current neutral grounding power systems from 1994 to 1997.The practical effects show that the problem of single phase-toground fault in small current neutral grounding system is satisfactorily solved.