Practical Considerations for Single-Pole-Trip Line-Protection Schemes

This paper discusses some practical aspects of implementing single-pole tripping schemes in transmission-line protection. Implementation and techniques will vary in the design of protective relaying systems that implement single-pole trip (SPT), as well as in the philosophy of the users applying these devices; however, the intent is to discuss issues that need to be considered for SPT systems. We present a quick review of the benefits and implementation of SPT, emphasizing the benefits for power system stability with a relatively minor incremental cost compared to three-pole trip (3PT) systems for EHV and many HV transmission systems. We also discuss specific aspects of implementing single-pole-tripping in line-protective relaying schemes. In addition, we discuss using a faulted-phase selection algorithm, some reclosing scheme philosophy, and the greater flexibility that improved communication channels give to SPT systems. We analyze the open-pole period of an SPT system to gain some insight into the behavior of the measured quantities and protective relaying elements