A transformer differential protection algorithm is proposed based on the third-order dynamic time warping (DTW). This method makes use of the current sample value within the bilateral data window of differential protection to constitute the shortest distance matrix. Via the shortest distance searching algorithm

a shortest path can be found in the matrix and take the average value of local shortest distance elements in the matrix through which the path passes as the differential current of bilateral sample current. Should data delay and data packet-loss happen in a digital substation for communication reasons

by using this differential protection algorithm

protection malfunction due to external faults can be avoided and protection can act reliably during internal faults. Simulation has verified the action performance of conventional phase differential protection and DTW differential protection during external or internal faults in different delay circumstances and different packet loss rates conditions. The results show that DTW differential protection has obvious advantages over conventional phase differential protection in delay-resistant

packet loss-resistant performance and sensitivity.