Selective detection of simple grounding faults in medium voltage power networks with resonant earthed neutral system

In this paper the influence of the medium voltage lines insulation ageing on some network parameters, namely the capacitive zero-sequence impedance of the network, the zero-sequence impedance of the grounding and arc-suppression coils taken together, as well as the equivalent zero-sequence impedance as seen from the grounding fault location, is analyzed. As a result of the analysis useful criteria to selectively detect faulty lines during a single grounding fault are formulated. These criteria are implemented by a digital protection block BYCD - 2. Measurements done in a real medium voltage network, during purposely provoked faults, validate the concepts the block is based on.