Pilot Protection for Transmission Line of Offshore Wind Power Based on Directions of Fault Current Variation and Cosine Distance

The grid-connected offshore wind farm via voltage source converter based high voltage direct current transmission (VSC-HVDC) is an important part of new energy power generation. When its AC transmission line fault, it presents a fault characteristic that is obviously different from the traditional power grid. This makes the traditional pilot protection face the risk of decreasing sensitivity or even refusing to operate. Therefore, the fault current on both sides of the line will change in the same direction when an internal fault occurs. When an external fault occurs, the fault current changes in the opposite direction. This paper forms the protection principle according to this characteristic. The cosine distance algorithm is selected as a method to measure the correlation between the direction of fault current changes on both sides. A new pilot protection method for transmission line of offshore wind power based on directions of fault current variation and cosine distance is proposed. The feasibility of the protection method under different fault types and transition resistances is verified by simulation.