Performance of negative sequence pilot protection applications in transmission line with open-phase operation

The performance of the negative sequence pilot protection (NSPP) is less deteriorated by the phase-ground shunt capacitance since the negative sequence current loops in phase-phase lines. Hence NSPP is a good candidate for the main protection in UHV lines with the special characteristic of larger charging current. But as we all known, NSPP is not suit to the open-phase operations in transmission line, which limited its wide applications in HV/EHV lines in history. In response to this question, the performance of NSPP in transmission line with open-phase operation is analyzed, and the mal-operation reason of the NSPP relay is discovered. Then an improved algorithm for faults detection is proposed in open-phase line, and the simulation results verified its validity. The work in this paper is only the basic steps, the more research, such as the sensitivity and transient characteristics of ground fault detections in open-phase line should be discussed further.