A Real-Time Synchrophasor-Based Zone-3 Supervision of Distance Relays Under Load Encroachment Condition

This paper deals with the implementation of a real-time supervisory protection algorithm to avert the mal-operation of third zone element of distance relays during load encroachment. The proposed supervisory algorithm controls the operation of the backup zone (Zone-3) of distance relays by analyzing the synchrophasor data obtained from the phasor measurement units (PMUs) located throughout the power system network. The combination of the inherently higher delay time of Zone-3 element and the latency associated with PMUs to communicate information to the central control center makes the algorithm suitable for transmission line protection. The superiority of the proposed method is verified by conducting extensive real-time experiments on a laboratory model for a 400-km extra high voltage transmission line and implementing the protection algorithm on the LabVIEW platform at the System Protection and Control Centre. PMUs have been realized using National Instruments (NI) Compact Reconfigurable Input-Output embedded controllers, and the synchrophasor estimation algorithm is deployed using LabVIEW field-programmable gate array software. The results obtained from the experimental setup validate the viability of the proposed algorithm for the real-time implementation.