New algorithms for earthfault distance protection in insulated and compensated networks

Abstract

Through the analysis of transient signals after the occurrence of an earthfault it is possible to evaluate fault direction and fault distance. The faulty line is simulated by using a three phase Tl‐model. The result is a differential equation of a higher order, which only consists of voltages and currents, which are measured at the installation point of the relay. If the capacities of the part of the network without earthfault are considerably larger than those of the faulty line, the line capacities of the faulty line can be ignored in the differential equation. This results in afirst‐jorder differential equation, which can be solved by integration in the time domain. A second algorithm takes the line capacities into consideration. The derivatives of the input signals are calculated in the frequency domain. A third algorithm calculates the equivalent fault inductivity in the frequency domain by complex division. The last algorithm deals with the line capacities by using correction factors. The mode of operation of the earthfault distance algorithms presented here will be shown with the example of a 22‐kV‐overhead line network.

SLG(Single-Line-to-Ground) Fault Location in NUGS(Neutral Un-effectively Grounded System)

“…In ref [7], a method using the Fourier-transform to calculated the line impedance in frequency domain. The reactance of the faulty line length is obtained directly as the imaginary part of the impedance calculated from the corresponding frequency spectrum components of the voltage and current.…”