A Novel Pilot Protection Based on Transient Current Time-Frequency Matrix Distance for Power-Frequency Transmission Lines Connected to M3C

The limited fault current amplitude and controlled phase angle of M3C power frequency side AC line lead to low sensitivity and speed reduction of traditional pilot protection. To address the problem, this paper proposes a novel pilot protection based on transient current time-frequency matrix distance for power-frequency transmission lines connected to M3C. By analyzing the transient current analytical expression of the synchronous generator side and the M3C side in the time domain, which concluded that in the time-frequency domain, the fault current on the M3C side has obvious dynamic offset in the fundamental frequency component compared with the fault current on the synchronous side. In view of this difference, the S transform is used to extract the time-frequency characteristic matrix of the fault current, and the principal component analysis (PCA) is used to reduce the dimension of the high-dimensional time-frequency matrix to improve the speed. The time-frequency matrix distance is introduced as a protection criterion to quantify the difference in time-frequency characteristics of transient currents on both sides, which is used to distinguish internal and external faults. The matrix distance of external faults is greater than 0.8, and the matrix distance of internal faults is less than 0.5, which is significantly different. The simulation results show that the method takes into account both high sensitivity and speed.