The main indicators to measure power quality are voltage, frequency and waveform. In a general sense, high-quality power supply refers to voltage quality, current quality, power supply quality and power consumption quality. It can be defined as the deviation of voltage, current or frequency that leads to the failure or failure of electrical equipment, including frequency deviation, voltage deviation, voltage fluctuation and flicker, three-phase imbalance, instantaneous or transient overvoltage, waveform distortion (harmonic), voltage sag, interruption, rise and power supply continuity.

        It is necessary to carry out real-time continuous on-line monitoring of power quality in order to determine its quality problems. The advantages of online power quality monitoring are as follows:

        The continuous monitoring data generates a detailed power quality monitoring report in the database, which provides a basis for analyzing power quality accidents and clarifying the causes of accidents, so as to provide reference for avoiding the recurrence of accidents and realize predictive maintenance.

        Online monitoring of harmonics to ensure that over time, the increase of load will not cause too much heat, affect and shorten the normal service life of electrical equipment.

        On line monitoring of power consumption and RMS (root mean square or RMS) provides a basis for system capacity expansion, adding new loads and ensuring sufficient capacity of power supply feeders and substations.

        Online monitoring can timely monitor power quality problems, send alarm information through communication network or alarm equipment, and inform staff to take timely measures to isolate faults and reduce hazards.

        Therefore, the power quality on-line monitoring system enables the power department to comprehensively and accurately grasp the power quality status of the power supply system, make a comprehensive evaluation of the power quality level of the power grid, and then find out the causes of disturbance and reduce the impact of disturbance for treatment, so as to help the power supply company correctly improve the structure of the power supply system in the planning, Improve the stability of system operation and reasonably expand the capacity and investment level of the system. Therefore, long-term monitoring of power quality of the system is a necessary work of power quality management.