Current Amplitude Ratio Based Pilot Protection for the transmission Line Connected to Inverter-interfaced Renewable Energy Power Plants

The internal impedance of inverter-interfaced renewable energy generators (IIREGs) is unstable and its phase angle is affected by control systems, so the ratio braking style differential protection faces great challenges. To solve this problem, a pilot protection method based on current amplitude ratio on both sides is proposed. The method only needs to transmit the scalar signal which reduces the requirements on the communication system and synchronizing ability. It can operate correctly in the case of reclosing on permanent faults and weak output of the power plants. In addition, its principle is simple and reliable, and only requires a conventional sampling frequency and a computation speed. These features make it become a good choice for industrial application. The simulation results show that the protection method can correctly distinguish internal and external faults and field-testing data also confirm the effectiveness of the method.