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Power capacitors and their main characteristic parameters
power capacitors are the main components of reactive power compensator. With the development of technology and technological renewal, paper dielectric capacitors have been replaced by self-healing capacitors. Self-healing capacitors have been evaporated on both sides of dielectric as electrodes. The biggest improvement is that the dielectric insulation of the capacitor has natural recovery performance when the dielectric breaks down, that is, when the dielectric partially breaks down, the metal coating near the breakdown place will melt and vaporize and form a cavity. This will cause the reduction of the plate area to reduce the capacitance C and the corresponding reactive power, but it does not affect the normal operation of the capacitor. The main characteristic parameters of self-healing capacitor are rated voltage, capacitance and reactive power.
1. 1 rated voltage GB 1274721991 "self-healing low voltage shunt capacitor" regulation 3. 2 states that "capacitor rated voltage priority values are as follows: 0. 23. 0.4 0.525 and 0.69 kV. "the capacitor rated voltage selection is generally 5% higher than the rated operating voltage of the electrical equipment. 1. 2 the capacitance of the capacitor is the ratio of the charge on the plate to the voltage between the electrodes, which is related to the area of the plate, the thickness of the insulation between the plates and the dielectric coefficient of the dielectric. The formula is C = 14 π ε × S D, in which ε is the dielectric coefficient of the insulator between polar plates. S is the area of capacitor plate; D is the thickness of insulation layer of capacitor.
2. In the above formula, the capacitance C value has no direct relation with the voltage. C value only depends on the area of the capacitor plate and the insulation medium, but this is only the static state of the capacitor when the grid is not in operation. After the grid is put into operation, due to dielectric breakdown caused by the reduction of the polar plate area, which will affect the value of capacitance C, so in the operation process, capacitance C is a decreasing variable year by year. The attenuation rate depends on the operating voltage condition and its own steady overvoltage capability. The capacitance value of an outgoing capacitor is defined as a static capacitor. In general, the drop rate of capacitance value should be less than 2% in the first year of operation, and 1% in the second to fifth year. After the fifth year, the capacitance value will decrease more quickly because of the aging of dielectric. When the capacitance value drops below 85% of the capacity at the time of the factory, the life of the capacitor can be considered to be over.
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