Fault Locator

Author: Dr. Juergen Holbach and Michael Claus, Siemens PT&D, USA

Introduction

Single-ended fault locators are normally based on an impedance measurement. Only the fault reactance is used to determine the distance to the fault. The distance protection is based on the same principle. All protection engineers know about the limitations of this measurement and use only 80-90% of the line impedance for a zone 1 setting. Even more difficult for the fault locator is, that an accurate measurement is expected along the whole line and not only on one setting point like on the distance protection function. This is especially a challenge for lines with a non linear impedance distribution along the line. In the diagrams of figure 1 is an evolving fault shown on a 50 miles long line. The fault was at 5 miles from the shown location. The figure shows the signals of a C-G fault on the parallel line with a BC evolving fault on the actual line after approx 2.5 cycles. The fault locator result from the single ended fault location from both ends (red) and the double ended fault locator (blue/green) are presented in Figure 2. The common factors that influence the accuracy are described below. Hereafter, the fundamental improvement provided by the "two ended" fault locator, which in addition uses the measured values from the opposite line end, are described.

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