Impact Of LVRT Of Wind Turbine Generators On Transmission Line Relay Protection

Relay protection is critical for security and stability of power systems. With quickly increasing integration of wind powers recently, their participation to gird fault can not be ignored. Wind turbine characteristic differs from traditional synchronous generator, therefore, relay protection configuration must consider its influence.Based on the wind turbine fault current characterisitic, combining with the low voltage ride through (LVRT), this paper analysis the impact of wind farm on relay protection on its export transmission line. The work includes the influence of squirrel cage induction generator (SCIG) with LVRT measures on overcurrent protection, the characteristic of short circuit current of doubly fed induction generator (DFIG) considering LVRT measures and the impact of crowbar on the two sections current protection of transmission line in distribution network..The details as the following:1) For the wind power system with SCIGs, impact of LVRT measures, i.e. series braking resistors (SBR) and static var compensator (SVC), on short current components and overcurrent protection is analyzed.2) Considering stator transient, control to rotor-side converter (RSC), voltage angle change, as well as current of grid-side converter (GSC) of DFIG, the short-circuit current expression without crowbar operation is deduced. Considering the stator resistance, voltage angle change, and current transient of GSC, the short current expression with crowbar operation is deduced.3) Ansysising the short circuit current expressions, the post-fault steady-state and transient equivalent model of DFIG are obtained by the steady-state and transient component. Furthmore, the possible error produced by the simplification of the process.4) Considering the activation time of crowbar, the rotor voltge constant, the value of crowbar under different steady-state condition of DFIG is obtained. Then, analysis the impact of crowbar and its value on the two sections current protection of transmission line in distribution network.