Problems that should be paid attention to in operation of power capacitor (III)

4. Working current and harmonic problem

When capacitors work on power grids containing magnetic saturation regulators, large rectifiers and electric arc furnaces, high-order harmonics will appear in alternating current. For n harmonics, the capacitor reactance will be fundamental when 1/n, therefore, the harmonic effect on the current is very powerful, the equivalent of the voltage influence degree of N2 times. For example, as far as the 5 harmonic is concerned, if its reactive power is 6% of the fundamental wave, the voltage it causes is only (1/5) x 6%=1.2% of the rated voltage of the fundamental wave, and the current provided by it is 5 * 6%=30% of the base wave current. This current of harmonics is very harmful to capacitors, which makes it easy for capacitors to breakdown and cause interphase short circuit. Considering the existence of harmonics, it is stipulated that the working current of capacitors should not exceed 1.3 times the rated current. If necessary, a suitable inductive impedance should be connected to the capacitor to limit harmonic currents.

5. The problem of arc light during closing

When some capacitor banks, especially high voltage capacitors, are connected to the grid, there will be arc light on the circuit breaker or the converter because of the large inrush current. In this case, the capacitor value of the capacitor bank should be adjusted or the converter should be replaced. The series reactor can be used to eliminate the high voltage capacitor.

6. The problem of radio sound in operation

7. Explosion problem

When a plurality of capacitors are running in parallel, if one of them breaks down, the other stations will pass through the discharge at the same time.

The discharge energy is very large, and the pulse power is very high, which makes the capacitor oil vaporize quickly, causing explosion and even fire. In order to prevent such accidents, an appropriate reactor or fuse can be connected to each capacitor in series and run in parallel.