An improved scheme for the detection of permanent and transient earthed faults in reactor-compensated transmission lines

Three-phase reclosure with dead time is widely applied in robust grid, but its blind reclosing in the case of permanent faults or arcing transient faults may cause serious damage in power system. It is important to detect the nature of an earthed fault before reclosing for three-phase reclosure, which is helpful to improve successful reclosing rate and meet the increasing requirement on self-healing ability in smart grid. Some researchers have developed schemes based on parameters recognition in relaying protection, which is independent of damping direct current component and various harmonic components etc. On the basis of the discussion of parameters detection of zero-mode equivalent model in transient faults without arc, the proposed model is acted as reference model to develop nature detection scheme of earthed faults using model parameters recognition. Moreover, this paper put forward detection criterions of permanent earthed faults, which are based on the parameters recognition such as the inductances of shunt reactors, neutral reactor and the inductance combined by the former respectively. After analyzing the performance and applicability of the proposed criterions theoretically, the criterion based on inductance of neutral reactor is of better performance than the others in earthed faults. Simulations under different conditions show that the optimized detection scheme in earthed faults is of higher sensitivity and reliability.