Power quality problemsINTRODUCTION        Power quality problems have become serious and common issues that are being discussed due to its effect on power system networks. Any variation in voltage, current, or frequency which may lead to an equipment failure or malfunctions is potentially a power quality problem. According to IEEE standard 1159-1995, a voltage sag is defined as a decrease to between 0.1 and 0.9 p.u. in root mean square (rms) voltage at the power frequency for durations of 0.5 cycle to 1 min.        A power system fault is a typical cause of voltage sag and have been the vast contribution of power quality problems. Other typical causes of voltage sag includes of starting of large induction motor, transformer energizing and load changes. When a system is faulted, the voltage on the particular phase will drop to certain amount and sometimes drop to zero. When certain voltage drops to zero, particularly it will become an interruption. Interruption cant be tolerated as it gives a very bad impact to the utilities.
