Computation of Energy Loss in an Induction Motor During Unsymmetrical Voltage Sags—A Graphical Method

Symmetrical and unsymmetrical voltage sags are a major cause of energy loss in induction motors affecting the efficiency and longevity of the motor. A comprehensive and novel graphical method to determine energy loss during unsymmetrical sags is proposed. The energy is computed using torque-speed characteristics of the induction motor. Due to unbalance in the voltages during unsymmetrical sags, oscillations are observed in torque-speed characteristics. Throughout these oscillations, motor torque and speed attain extreme values. Area under the curve of torque and speed during oscillation is computed using MATLAB/Simulink simulation, which is a measure of the output power during unsymmetrical sags. The sag duration is measured to compute the energy loss. The analytical expression to assess output power of an induction motor during unsymmetrical sag is derived. The graphical results are validated using analytical calculations. Graphical representation is easy and faster to construct than analytical methods; in addition, the graphical method proposed makes it easier to assess the comparative magnitudes. Assessment of energy loss provides a useful tool for optimal injection of energy for sag mitigation techniques.