Overreaching of Reactive Reach in Distance Protection Relay for Faults Involving Earth Path and Soil Resistivity as a Limiting Determinant

Overreaching has been a major concern in the transmission line network. Line differential protection to tackle the issue is not available at times due to various constraints (Monetary, OPGW network etc.) Overreaching by a relay at a local bus due to a fault in some other line at remote bus is a major concern as it leads to the blackout in a LILO (Loop-In Loop-Out) substation. Such a scenario occurs during lightning faults and solid ground faults of low resistive nature. Weak infeed from remote end also elevates the condition of overreaching. The following is a case study of such a fault and the steps taken to rectify it. It is a comparative study of the effect of change in “earth/residual compensation factor” on the reactive reach of the relay setting. Changes in the value of earth compensation factor is done by trend analysis of fault in lines over a period of time considering the physical factors associated with the calculation of earth compensation factor.