Power quality disturbances such as voltage sag, transient, swell and harmonic are serious problem to the power system equipments. The power industry faces a big challenge due to these disturbances. These will cause many problems for influenced loads such as malfunctions, instabilities and short lifetime. Voltage sags are short-durations in RMS voltage due to faults, motor starting and transformer energizin, switching of heavy load, typically caused by a loose connection and the most common power quality disturbance.
Noor Khumairah Othman (Mon,) studied this question.