Algorithm for the study of voltage sags on induction machines

This paper proposes an algorithm for the approximate calculation of the effects caused by a voltage sag in the induction machine supply system. The algorithm computes the current and torque peaks, and the mechanical speed loss for an extensive range of voltage sags. It has a high calculation speed because it makes two simplifications. The first supposes that speed varies insignificantly during the first cycles after the voltage drop and recovery points to solve analytically the electrical transients in these cycles. The second neglects the electrical transient during the sag duration for a quick evaluation of the speed loss. Machine sensitivity to voltage sags is graphically shown. The curves can be applied to protective relay coordination.