Impact of Inverter-Interfaced Renewable Energy Generators on Distance Protection and an Improved Scheme

With different structures and control strategies, inverter-interfaced renewable energy generators (IIREGs) have different fault characteristics from synchronous generators. This makes the conventional distance protection used in networks with synchronous generators not applicable for transmission lines emanating from IIREGs. Therefore, supported by the fault current analysis, operating performances of distance relays on both sides of the transmission line are unveiled. It reveals the problem that the conventional distance relay on the IIREG side has a high risk of malfunction or refusing to operate. To cope with this adaptability problem, an improved scheme based on time delay and zero-sequence impedance is proposed. To validate the operating performances of the scheme, a detailed IIREG model is built in Real Time Digital Simulator (RTDS) and simulation tests are carried out. Apart from these, a field short-circuit test is performed in a real wind power plant to examine the practical feasibility of the proposed scheme. Both the simulation results and the field test confirm the problem of the conventional distance protection and verify the reliability of the improved scheme.