Safety capacitors requirements for operating current and voltage

Safety capacitors are one of the indispensable capacitors in our lives and are widely used in circuits. Recently, some customers have asked questions: "I bought the wrong safety capacitors. The voltage withstand voltage of the capacitor is different from the withstand voltage of the circuit. Can it be used?" The answer is no, voltage and current will affect the capacitor.

If the voltage is a little higher, it can be used, and it cannot be too high. Safety capacitors are very sensitive to voltage changes. Long-term overvoltages can cause severe heating of capacitors, capacitor insulation can accelerate aging, life is shortened, and even electrical breakdown or thermal breakdown occurs. The grid voltage should generally be lower than the rated voltage of the capacitor itself. The long-term power-frequency steady-state over-voltage should not exceed 1.1 times the rated voltage. Therefore, the shunt capacitor device should operate at the rated voltage. Generally, it should not exceed 1.05 times the rated voltage. The operating voltage should not be Exceeding 1.1 times the rated voltage.

The current can be used if it is only a little higher, not too much. When safety capacitors work on a grid with a core-saturated device, high-order harmonics appear during operation. For n-order harmonics, the reactance of the capacitor will be 1/n of the fundamental, so harmonics current will be significant. increase. The harmonics current is very harmful to the capacitor, and it is easy to cause breakdown of the capacitor due to heat generation. Considering the existence of harmonics, the working current of the capacitor must not exceed 1.3 times of the rated current. If necessary, the appropriate reactance should be connected in series with the capacitor (series reactor). ) to suppress harmonic current.

The current and voltage of the safety capacitors must also meet their rated current and voltage in order to operate stably.