Improved Variable-Quantity Distance Protection Method Based on Impedance Compensation Under Phase-to-phase Fault Conditions

In synchronous condenser-wind farm integrated transmission systems, the inherent asymmetry between positiveand negative-sequence impedances constitutes a critical limitation for the proper operation of sudden-impedance-based distance protection. To address this challenge, this paper proposes an enhanced protection scheme incorporating setting impedance compensation. The methodology involves: firstly, real-time computation of system sequence impedances to derive the composite equivalent impedance; secondly implementation of a compensation impedance, calculated as the difference between the original positive-sequence impedance and the equivalent composite impedance during phase-to-phase short-circuit conditions; and thirdly imposition of a security constraint ensuring the modified setting impedance remains below the total line impedance to prevent maloperation. Extensive Simulink simulations validate the proposed method’s efficacy, demonstrating both reliable operation for phase-to-phase faults at the transmission outlet of synchronous condenser-wind farm systems and significantly improved tolerance to fault resistance effects.