Electric energy can also be seen as a kind of commodity entering the market. Like other commodities, it is undoubtedly necessary to pay attention to quality. Electric energy is a kind of material that can't be touched or seen, but it is real. How can we distinguish its quality? This is a more complex problem. Through the power quality on-line monitoring device, the power quality of the power grid system is monitored on-line in real-time, and the indicators of power quality are analyzed to judge whether it is good or bad.

Power quality refers to the quality of AC power supplied to users through public power grid. In an ideal state, the public power grid should supply power to users with constant frequency, standard normal wave and rated voltage. At the same time, in the three-phase AC system, the amplitude of each phase voltage and current should be equal, and the phase symmetrical phase difference should be 120 degrees. However, due to the nonlinearity or asymmetry of generators, transformers and lines in the system, the nature of the load is changeable, and the control means are not perfect, and the operation, external interference and various faults and other reasons, this ideal state does not exist. Therefore, there are various problems in the operation of power equipment and power supply and consumption in the power grid, which leads to the concept of power quality.

Power quality monitoring is a complex system engineering. It involves power system, automatic control, modern communication and so on. The scale of modern power grid is becoming larger and larger, and the monitoring points are more and more. The monitoring of live energy quality is not only limited to a certain point, but also to realize the unified power supply system, power quality monitoring of different locations, and even centralized monitoring of multiple different power supply systems. In terms of function, more emphasis on intelligence, in addition to calculation, display and other functions, but also a certain degree of judgment, analysis, decision-making and other functions.