A DFIG Wind Farm Collective Line Protection Based on Composite Modulus Current Difference Factors

To address the contradiction between the existing collective line protection and the transformer protection fuse of generators in new energy stations, in this article we propose a station collective line protection method based on the composite modulus current difference factors. The first step involves establishing a unit transient model suitable for the combination of electricity line protection. On this basis, the 1-mode and 2-mode current expressions of the collective lines fed into the bus are obtained with the effect of the phase change of the transformer taken into account, and an AC system fault attachment network with fault power supply is constructed. Further, the fault direction is determined by comparing the difference characteristics of composite modulus current flowing into the collector port under the two conditions of internal and external faults of the collective lines. A current protection criterion is subsequently established by constructing a difference factor of composite modulus current based on the principle of model parameter variation in both internal and external fault scenarios. Finally, the RT-LAB simulation results validate that our method is accurate and is capable of realizing the protection coordination between the collective line and transformer protection fuse. Moreover, it possesses the attributes of not expanding the fault cutting range, remaining unaffected by both new energy characteristics and high resistance ground.