Development of a Substation-Area Backup Protective Relay for Smart Substation

A substation-area protective relay is proposed to overcome the inherent defects of the traditional backup protection system. The relay performs local backup protective functions for the whole substation and its connected transmission lines. The setting coordination of backup protections will be simplified by this relay with a shorter fixed time-delay. The algorithm of locating the faulted component employs the current differential principle with a self-adaptive restraint characteristic. The current sampled values are obtained by process-level networks inside the smart substation and by wide-area Ethernet between adjacent substations. The relay also works with the breaker states and the tripping generic object oriented substation event (GOOSE) from primary protections. A prototype based on the proposed scheme and IEC61850 standards has been developed by digital signal processor / field programmable gate array. The performance of the prototype was evaluated through the complete digital testing system using real time digital simulator / gigabit transceiver network and a communication simulator. Tests were carried out under different typical scenarios, such as fault transition resistances, inrush currents, current transformer saturations, and abnormal communications.