Fault identification method based on unified inverse-time characteristic equation for distribution network

Traditional inverse-time overcurrent (ITOC) relay adapts itself to the severity of the fault and can be used for fault identification in the main/backup relays. A fault identification method based on a unified inverse-time characteristic equation is proposed to aim at the problems of large setting workload and easy misoperation of inverse-time overcurrent relay after distributed generation access. It does not require a step-by-step setting and communication, and can realize adaptive coordination of multilevel relays. Firstly, the distribution law of positive sequence fault component voltage and the influence of distributed generation on its distribution characteristics are analyzed. Secondly, the setting principles and problems in implementing a unified equation for the multilevel coordinated relays are analyzed for the standard ITOC characteristic equation. The functional form of the user-defined inverse-time characteristic equation is derived from the ITOC equation and the setting principles considering the influence of fault conditions are given. The expression of the unified inverse-time characteristic equation is given, and the action sequencing of the adaptive fault position is obtained from the calculated tripping time. Finally, the simulation results validate the effectiveness of the proposed method.