Computation of stored energy in an induction motor during symmetrical and unsymmetrical voltage sags

The ride through capability of an induction motor depends on the stored energy in the winding inductances and the rotor during voltage sags. This paper presents an analytical method to determine stored energy in the induction motor during symmetrical as well as unsymmetrical voltage sags. Voltage sags causes losses in the motor energy that influences its performance. Under such circumstance, the already stored energy in the motor comes in to action and tries to satisfy the energy deficiency for the rated output. Impact of voltage sag also depends on type of load. Two most commoc load types viz. constant load torque and variable load torque are exhibit measure of the quantum of stored energy during voltage sags. This study with the help of analytical assessment brings forth the fact that the adverse effect of voltage sags on constant load torque is more vulnerable than the variable load torque. In addition, the role of stored energy to differentiate between vulnerable and tolerable voltage sags during symmetrical and unsymmetrical voltage sags has been presented analytically. The analytical results are checked by simulating the conditions for different types of sags in MATLAB/SIMULINK.