Design of a Distance Relay Using Adaptive Data Window Filters
Ghotra, Daljit Singh
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Transmission lines are generally protected by distance relays. Most distance protection relays presently available use microprocessor technology. They estimate fundamental frequency phasors from the quantized values of voltage and current samples. The relays use filters that use fixed sample data windows of one cycle of the nominal frequency. Therefore, the transient response of the filter is about one cycle and the estimated impedances do not converge before this time. However, it is possible to use different lengths of data windows at different sampling instants and improve the transient response. This thesis describes a distance relaying technique, which uses adaptive data window filters. Relay algorithms that use adaptive data window filters and fixed data window filters were also developed and their performances were compared by using data from simulations using the electromagnetic transient program, EMTDC/PSCAD. Results obtained from a sample power system and a part of the SaskPower transmission network are presented. Different operating conditions of these power systems and, faults of different types and at various locations were simulated for performance evaluation. It was observed from the simulation results that the seen impedances obtained using the adaptive and fixed data window techniques converged to the same values. The results indicated that the convergence of the seen impedance was significantly faster when the algorithm using the adaptive data window technique was used. Selected results are presented in the thesis. The adaptive data window technique and the fixed data window technique were implemented to form prototype distance relays using a general-purpose relay. The hardware and software constituents of the relay are presented in this thesis. The relays were tested using the Real-Time Playback Simulator (RTPS) for a variety of faults simulated on a part of the SaskPower system using the EMTDC/PSCAD program. The procedure for testing the relay by using a playback simulator is reported.. The test results indicated that the relays operated correctly for all the faults simulated inside the protection zone and did not issue a trip command for the outside faults. The test results also confirmed that the adaptive data window-based relay is able to issue trip commands in lesser time compared to the time taken by the fixed data window-based relay, while the impedances computed by both relays converged to the same values. Selected results are included in the thesis.