Improved superimposed current phase selector of wind farm with crowbar system

Superimposed current phase selector (SCPS) is commonly used in transmission line protection, but it is affected by the distinction between positive and negative sequence impedances. However, this problem becomes more pronounced when it used in wind farm. In this paper, performance of SCPS is analyzed first considering the wind farm with crowbar system. It is exposed that amplitude and angle of wind farm positive and negative sequence impedances will differ significantly when crowbar system is activated, which could possibly paralyzes SCPS. Then an improved phase selection scheme is proposed, and the superimposed current is compensated by positive sequence fault current to eliminate impedances difference. Finally, simulation is performed to support the proposed scheme.