In the whole power system, the online power quality monitoring device plays an irreplaceable role. According to the power quality standard, it can continuously track and monitor the voltage deviation, frequency deviation, harmonic, voltage fluctuation and flicker, three-phase imbalance and other indicators.

The voltage deviation is that the actual voltage amplitude changes slowly and deviates from the rated voltage in a certain period of time. Bias is steady state, that is, we often say that the voltage is high or low. The magnitude of voltage deviation mainly depends on the operation mode of power system, line impedance and the change of active and reactive load.

The influence of voltage deviation on the normal operation of power grid system is relatively large. When the system operating voltage is low, the limit of transmission line will be greatly reduced, which may cause the instability of system frequency, even lead to frequent collapse of power system, and bring great losses. However, the operation performance of electrical equipment is deteriorated, the output of power supply is reduced, and the power transmission capacity of transmission and transformation equipment is reduced. It is difficult for the motor to start. Long term operation will lead to motor burnout and reduce the utilization rate and economic benefits of electrical appliances. The normal operation and product quality of the production process will be affected. Not only the operation efficiency will be reduced, but also the equipment will be damaged due to over-voltage or over-current.

When the power grid operates at high voltage, it will accelerate the insulation aging of electrical equipment, shorten the service life of electrical equipment, increase the harmonic of power grid and pollute the power system environment.

Therefore, it is necessary to conduct real-time on-line monitoring of power quality in the whole power grid, so as to develop high-quality power quality solutions.