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The short-circuit current value of distribution network is small when high impedance grounding faults (HIGFs) occur,which cannot be detected tripped by the traditional over-current protection devices. If short-circuit cannot be tripped in time,it will lead to serious results. To solve the above problems,the fault components of microgrid in the operating conditions of HIGFs are analyzed. The phase differences characteristics between positive-sequence fault component of bus voltage and positive-sequence current fault components in the feeders are explained in detail. And based on the phase differences characteristics,the fault criterion for HIGFs in distribution network is proposed. Meanwhile,to overcome those problems caused by the imbalanced distribution network,the starting criterion is proposed. Based on the above fault criterion and the starting criterion,the new fault detection method is proposed. Finally,a medium distribution with the model of overhead lines is established in PSCAD/EMTDC,and simulation results verify the correctness of the fault detection method.

[Introduction] The paper aims to study the transient stability of the wind power system and that how the injection of reactive power to the wind power system affects the stability. [Method] So we established the mathematic model of the wind power generator, the frequency converter, and a three-machine-nine-node power system model was constructed based on PSAT. We realized the the time simulation in condition of the three phase fault. [Result] Then we get the voltage and power angel figure of direct drive wind power system, double-fed wind power system and constant speed wind power system under different bus short circuit fault time. [Conclusion] It demonstrates that the wind power system has different stability based on different wind power generator, disturbance and duration.