What is the cause of capacitance attenuation of low voltage power capacitors

What is the cause of capacitance attenuation of low voltage power capacitors

tenco 2019-07-23

Low voltage power capacitor

In the operation of power capacitors, the following problems should be paid attention to: the power capacitors under the working voltage are very sensitive to voltage, because the loss of capacitor is proportional to the square of voltage, overvoltage will lead to serious heating of capacitor and accelerate aging.Capacitor insulation, shortened life, even breakdown.The grid voltage should generally be lower than the rated voltage of the capacitor itself, not more than 0% of its rated voltage.Therefore, when the operating voltage is twice the rated voltage, cooling measures must be taken.When power capacitors are installed in power grids with magnetic saturation regulators, large rectifiers, and arc furnaces, the working current and harmonic problems will generate higher harmonics in the ac.

For the NTH harmonic, the reactance of the capacitor will be base/n.Therefore, the harmonic current is very harmful to the capacitor, and it is easy to make the capacitor malfunction and cause the phase short circuit.Considering the existence of harmonics, it is stipulated that the working current of capacitor should not exceed 1.3 times of rated current.If necessary, appropriate induction reactors should be connected in series with capacitors to limit harmonic current.Since the impact current is large when the closed power capacitor bank, especially the high-voltage capacitor bank, is connected with the power grid, the arc problem in the closed power capacitor bank will appear on the switch or converter.In this case, adjust the capacitance value of the capacitor bank or replace the converter.Series reactors can be used to eliminate high voltage capacitors.

What is the cause of capacitance attenuation of low voltage power capacitors

1. High temperature aging

If the operating temperature is too high, the internal components will occur high temperature aging phenomenon, the metallized film will therefore service life attenuation, capacitance decline and other problems.

2. Over voltage operation

If the overvoltage runs, the operating temperature will increase to some extent. If the overvoltage runs for a long time, the operating temperature of the capacitor beyond the design range will shorten the service life of the capacitor, and also cause the capacitance attenuation.

3. Over current operation

At present, most low-voltage power capacitors in the market are self-healing capacitors. When running over current, the inner metallized film will have electric breakdown phenomenon, which will reduce the usable area of metallized film and slightly attenuate the capacitance. If the electric breakdown is too much, the capacitance will be seriously attenuated

4. Overload operation

Although low-voltage power capacitors can be overloaded, they are all limited by time, voltage and current, etc. If they are overloaded for a long time, the breakdown frequency inside the capacitor will be too high, the temperature will rise, and the service life of the capacitor will be reduced, the capacity will be seriously reduced, and even the fault will occur.