The low voltage ride through（LVRT） capability is one of the most important problems in the large-scale wind generators connecting to the distribution grid. Since the most voltage sags in the system are caused by faults in feeders， the voltage sags propagation characteristics is key to the design of control strategy of LVRT for wind turbines. In order to enhance the LVRT capacity of wind farm by shortening fault duration from the point of the feeder protection， the profiles of line voltage variations at the fault point are presented with different un-balance fault situations. The extreme voltage aberration and the occurrence conditions in different earthing resistance and residual situations are quantified. The uncommon extreme sags with phase-phase faults is discovered， which may cause the mis-operation of relay. It is also found that the main factors causing extreme sags with phase-ground fault is the value of residual degree factor.