The Research On Fault Line Selection Non-Solid Earthed Networks

The non-solid earthed neutral, also isolated or Petersen coil compensated neutral, is adopted widely in medium voltage distribution networks in China. But the existing earth protections are not suitable in practical situations due to the nature of weak fault capacitive current and unstable fault arc in this network. Therefore, on the basis of detailed analysis of the amplitude characteristics of transient currents in single phase earthed distribution network with non-solid earthed neutral, two novel earth fault protection methods with transient zero sequence and phase signals in special amplitude and frequency bands are presented in this paper. The faulty feeder is selected by comparing the amplitude of selected component of transient zero sequence currents and transient phase currents of all feeders respectively.Based on the characteristics of a single phase earthed distribution networks as follows: the amplitude of transient zero sequence current in faulty feeder is larger than that in healthy feeder, a synthetic algorithm comparing the amplitude of the transient zero sequence currents of most feeders is proposed in this paper. This algorithm is made up of two sub-algorithms: the one based on the amplitude comparison of transient zero sequence current in a self-adaptive special frequency band, and the other based on the amplitude comparison of active components of zero sequence current in low frequency band (around 50Hz). The former using the transient signals in the first capacitive band is suitable for obvious fault in compensated networks and all kinds of fault in isolated networks. In the compensated networks, the active current component of the resistance that is connected in series (or parallel connection) with Petersen coil flows only through the fault feeder. Based on this principle, the latter is suitable for weak fault in compensated networks, which is through comparing amplitude of active components of zero sequence current to select the faulty feeder. The synthetic algorithm is suitable for all kinds of fault and has higher sensitiveness and veracity.Finally, Simulation of MATLAB is used in carrying out calculations to prove the algorithms are effective in feeders'selection.