1The three-phase voltage imbalance is specified in the national standard GB/T15543-2008 "Power Quality - three-phase voltage imbalance":Power quality monitoringdeviceThe allowable value of normal voltage imbalance at the public connection point is 2%, and it should not exceed 4% in a short time. For each user of a public connection point, the allowable value that causes voltage imbalance at that point is generally 1.3%, and should not exceed 2.6% in a short time.

2. The frequency deviation of the power system is specified in the national standard GB/T15945-2008 "Power Quality Power System Frequency Deviation": the standard frequency of China's power system is 50Hz, and the allowable value of frequency deviation is ± 0.2Hz. When the system capacity is small, the deviation can be relaxed to ± 0.5Hz, and the standard does not specify the limit of capacity size. In the National Power Supply Regulations, it is stipulated that the allowable deviation of power supply frequency for power supply bureaus is ± 0.2Hz for power grid capacity of 3 million kilowatts and above, and ± 0.5Hz for power grid capacity below 3 million kilowatts.

3. Voltage deviation, according to the national standard GB/T 12325-2008 "Power Quality - Voltage Deviation of Power Supply", the sum of the positive and negative deviations of 35kV and above power supply voltage shall not exceed 10% of the rated voltage; The allowable deviation of three-phase power supply voltage of 10kV and below is ± 7% of the rated voltage; The allowable deviation of 220V single-phase power supply voltage is -10%~+7% of the rated voltage.

4. Harmonics in public power grids, as stipulated in the national standard GB/T14549-1993 "Power Quality - Harmonics in Public Power Grids": the total harmonic distortion rate of voltage in public power grids at all levels of 6~220kV is 5%, 6~10kV is 4%, 35~66kV is 3%, and 110kV is 2.0%; The allowable value of harmonic current injected into the power grid by users should ensure that the harmonic voltage of all levels of the power grid is within the limit range. Therefore, according to the national standard, the voltage harmonic distortion rate generated by harmonic sources at all levels of the power grid is: 2.6% for 0.38kV, 2.2% for 6-10kV, 1.9% for 35-66kV, and 1.5% for 110kV. For power users of the 220kV power grid and its power supply, refer to this standard for 110kV implementation.

5. Voltage fluctuation and flicker, according to the national standard GB/T12326-2008 "Power Quality - Voltage Fluctuation and flicker", the long-term (2-hour) flicker value Plt at the public connection point of the power system meets: ≤ 110kV, Plt=0.1 At 110kV, Plt=0.8.