Distance Protection with Dynamic Trip Region for Lines Terminated by Inverter Based Resources

As renewables are increasingly connected to the grid through inverters, inverter based resources (IBRs) affect the performance of the line distance protection and cause mal-operation of distance relays. This paper proposes an improved distance protection scheme based on dynamic trip region. The key idea is to adjust the trip region of the distance relay in real time to ensure proper operation of distance relays. First, the limitation of the traditional distance protection is presented. Second, with different fault types, fault locations and fault resistances, the expression of apparent impedance is derived as functions measured voltages/currents, to avoid the impact of varying equivalent source impedances of IBRs during faults. Third, a dynamic the trip region is proposed to ensure reliability of the proposed distance protection. Numerical experiments prove the effectiveness of the proposed method.