Novel algorithm for earth-fault location in compensated MV-networks

Abstract

This paper presents a novel earth-fault location algorithm, which enables the estimation of the earth-fault distance in compensated MV-networks. The novelty of the algorithm is that the fault location can be calculated with reduced number of settings compared to prior-art methods. This improves the practical usability and accuracy of the earthfault location. The key idea of the novel algorithm is to provide a set of equations based on an equivalent circuit valid for singlephase earth fault so that for the first time four unknown variables can be determined, that is, the fault distance and fault resistance, but also the conductance and susceptance parts of the shunt admittance of the protected line. Until now it has been mandatory to give the shunt admittance value of the protected line as a setting to enable impedance based fault location computation in compensated MV-networks. With the suggested algorithm the earth-fault distance can be estimated without setting the shunt admittance value, although its influence is included in the method. In the paper, the basic theory of modeling the phase-to-earth fault loop and the challenges related to it are shortly reviewed first. Secondly, the theory of the novel algorithm is introduced. Finally, the performance of the novel algorithm is compared to one of the prior-art solutions. This is done using data from comprehensive field tests conducted in a typical rural 20 kV overhead line network with central compensation. The results clearly demonstrate the significance of the shunt admittance parameter in providing meaningful results when the prior-art methods are used. The results also show that the novel algorithm extends the application of computational fault location in terms of fault resistance from solid earth faults into low-impedance earth faults. However, the practically achievable maximum fault resistance of an earth fault that can be located with adequate accuracy is limited e.g. by the practical measurement accuracy of the whole measurement chain including the measurement transformers and the IED.