There were many accidents of large-scale wind turbines disconnecting from power grid in 2011.As singlephase-to-ground fault cannot be correctly detected,single-phase-to-ground fault evolved to phase-to-phase fault.Phase-to-phase fault was isolated slowly,thus leading to low voltage.And wind turbines without enough low voltage ride-through capacity had to be disconnected from the grid.After some wind turbines being disconnected from the grid,overvoltage caused by reactive power surplus made more wind turbines disconnect from the grid.Based on the accident analysis,this paper presents solutions to above problems,including travelling waves based single-phase-to-ground protection,adaptive low voltage protection,integrated protection and control,and high impedance fault detection.The solutions lay foundations in theory and technology to prevent large-scale wind turbines disconnecting from the operating power grid.
Dong, X.Z. Shi, S.X. Wang, B. Bak, D.J. Cao, R.B. Ren, L. Lan, L. He, S.E.
High impedance faults(HIFs) are easy to occur in collective feeders in wind farms and may cause the cascading of wind generators tripping. This kind of faults is difficult to be detected by traditional relay or fuse due to the limited fault current values and the situation is worse in wind farms. The mostly adopted HIF detection algorithms are based on the 3rd harmonic characteristic of the fault zero-sequence currents, whereas these 3rd harmonics are very easy to be polluted by wind power back-to-back converters. In response to this problem, the typical harmonic characteristic of HIF arc flash based on Mayr’s arc model is first analyzed, and the typical fault waveforms of HIF in wind farm are presented. Then the performance of the harmonic based HIF detection algorithm is discussed,and a novel detection algorithm is proposed from the viewpoint of time domain, focusing on the convex and concave characteristic of zero-sequence current at zerocrossing points. A HIFs detection(HIFD) prototype implementing the proposed algorithm has been developed.The sensitivity and security of the algorithm are proved byfield data and RTDS experiments.
Bin WANGJiang NIJianzhao GENGYuanyuan LUXinzhou DONG
