SPS Software Distance Protection Relay

Simulates a MHO distance protection relay for transmission line fault detection using impedance-based protection zones using SPS Software.

This example presents a complete implementation of a digital distance protection relay applied to a high-voltage transmission network. Two 735-kV, 200-km transmission lines link equivalent power systems transferring approximately 1660 MW between buses. The transmission line is protected by MHO-type distance relays located at both ends of the line.

The relay algorithm continuously measures three-phase voltages and currents and computes phase-to-ground and phase-to-phase impedances using Fourier-based phasor estimation. Fault detection is performed by evaluating whether the calculated impedances enter predefined MHO protection zones represented by circular characteristics in the impedance plane. Zone 1 protection covers 80% of the protected line, while Zone 2 extends to 120% to provide backup protection.

The model supports various fault scenarios including single-line-to-ground and phase-to-phase faults. It also demonstrates permissive trip communication logic, where relays exchange trip signals to accelerate fault clearing for remote faults detected in Zone 2.

Users can analyze impedance trajectories, relay operating regions, breaker opening delays, and protection coordination during transient events. The example provides insight into the practical implementation of transmission line protection systems and serves as a valuable educational and validation tool for protection engineers, researchers, and students working on power system protection studies.