The traditional power quality only includes three aspects: frequency, voltage and reliability (i.e. no power failure). Subsequently, some accidents and user complaints made people realize the serious harm of harmonics and three-phase imbalance in the power grid. Since then, enough attention has been paid to voltage fluctuation and flicker, which has been included in the power quality standard.

        Voltage drop is harmful to some equipment. For example, during chip test, when the voltage is lower than 85%, the tester stops working, and the chip and motherboard may be destroyed. For the influence of computer, when the voltage is lower than 60% and the duration is checked for 12 cycles, the calculation work is affected, such as data loss.

        Through power quality monitoring, the system background power quality indexes can be objectively evaluated, including the index value level, whether it meets the provisions of relevant standards, and which indexes have problems or have deterioration trend.