Assessment of voltage sag based on improved fault positions method

An improved fault positions method based on analytical expression is proposed for fault position selection to overcome the blindness of traditional methods.Considering the fault distribution and fault types of transmission lines,it divides the transmission lines according to the relationship curve between the voltage sag depth and fault distance and takes each division as a fault position.Thus fewer fault positions are set and their frequency of voltage sag is assessed by fault probability distribution.It calculates the critical points of different voltage threshold by the relationship curve to determine the vulnerable area.The application to IEEE 30-bus test system validates its correctness and practicality.It works for both symmetric and asymmetric faults of power grid of any size.