High-Frequency Fault Component-Based Distance Protection for Large Renewable Power Plants

Renewable energy sources (RESs) are directly or indirectly connected to the grid through power electronic devices and the short-circuit current exhibits characteristics such as limited amplitude, nonpower frequency, and controlled phase angle, which may lead to the malfunction of the RES-side distance protection on the transmission line. In order to solve this problem, a distance protection method based on the high-frequency fault component is proposed. The voltage drop caused by the fault has a full frequency component and this can be extracted by wavelet transform. After that, the high-frequency impedance models of the inverter-interfaced renewable energy generator and the doubly-fed induction generator are established and the frequency selection principle that makes them have the stable phase angle is determined. On this basis, the internal and external faults can be determined by comparing the magnitude of high-frequency operating voltage and high-frequency voltage at the fault point. This method eliminates the influence of frequency offset and weak feed of RESs using high-frequency signals generated by voltage drops at the fault point and can tolerate some noise. At the same time, due to the larger radius of impedance circle at the high-frequency range, this method has a strong ability to withstand the fault resistance. The experimental results and the field-testing data verify the effectiveness of the method.