Power quality is a topic that most electricity companies and even subscribers pay close attention to. A key factor in the review is the expansion of the use of new electrical equipment in the networks. The development of power electronics equipment such as microprocessors, computers, electronic devices, power supply systems, lighting systems and induction furnaces, etc., which are sensitive on the one hand and must possess the highest quality electrical power and on the other hand lack Delivering optimum power to these devices causes effects such as transient or oscillatory phenomena, decreasing or increasing voltage, waveform deviation, frequency shift, voltage imbalance and harmonics. The old reliability index is often used to express power quality in the power grid. In calculating the reliability of power utilities, they mainly base the rate of shared power outages and calculate the average rate of access to electricity. This index is defined as the ratio of the hours of electricity to subscribers and industries to the total hours of a year, and most electricity distribution companies operate with a confidence factor of more than 99.99%. But reliability is not enough to evaluate and express the quality of today's power networks.