Preventing Maloperation of Mho Distance Relays During Load Encroachment Conditions Through a Pilot Scheme

Distance relays are crucial components of power transmission systems, providing protection against faults and ensuring the stability and reliability of the electrical grid. However, under certain conditions, they may experience maloperations, leading to erroneous tripping or failure to trip during fault events. The proposed scheme incorporates a modified Mho characteristics for monitoring load impedance to improve loadability during load encroachment conditions and prevent false tripping. In addition, the pilot scheme Permissive Under reach Transfer Trip (PUTT) provides communication capabilities enhancing the relay’s accuracy in fault detection. Extensive simulations and tests are conducted using MATLAB/Simulink to validate the effectiveness of the pilot scheme in EMTP (Electro Magnetic Transient Program) environment. The results indicate that the proposed scheme achieves faster detection of remote circuit breaker operations by 520ms bypassing the Zone 2 set delay of 500ms also. The scheme offers a practical and cost-effective solution to mitigate the challenges associated with load encroachment and enhance the overall stability and reliability of power systems.