Power quality is the quality of power in power system. The ideal electric energy should be a perfectly symmetrical sine wave. Some factors will make the waveform deviate from the symmetrical sine, which will cause power quality problems. On the one hand, we study what influencing factors will lead to power quality problems, on the other hand, we study what problems these factors will lead to, and finally, we study how to eliminate these factors, so as to make power close to sine wave to the greatest extent.
First, the quality index of electric energy
Frequency: rated frequency: 50Hz；; Frequency deviation: 0.2 Hz (≥ 3000 MW system) 0.5 Hz (< 3000 MW system)
Quality standard: See the table below for sine wave voltage and current.
Harm and suppression of harmonics: it will have a negative impact on power grid, power equipment and communication;
Second, the allowable deviation of voltage
The operation index and rated life of electrical equipment are related to its rated voltage. When there is voltage deviation at its terminal, its operating parameters and service life will be affected, and the degree of influence will vary depending on the size, duration and equipment condition of the deviation. The voltage deviation calculation formula is as follows:
Voltage deviation (%) = (actual voltage-rated voltage)/rated voltage × 100%
The allowable deviation of power supply voltage for power quality (GB 12325-90) stipulates that the allowable deviation of power supply voltage at the power receiving end of the user is:
(1) The sum of absolute values of positive and negative deviations above 1)35kV power supply is less than 10%, and users with special requirements on voltage quality are+5% ~-5% of rated voltage;
(2) The users of high-voltage power supply and low-voltage power supply of 2)10kV and below are+7% ~-7% of the rated voltage;
(3) Low-voltage lighting users are+5% ~-10% of rated voltage.