The operating voltage of the High Voltage Capacitor can reflect the voltage of the busbar system of the substation and directly affect the life and output function of the capacitor. The active power loss inside the high-voltage capacitor is mainly composed of dielectric loss and conductor resistance loss, and the dielectric loss accounts for more than 98% of the total active power loss of the high-voltage capacitor. The dielectric loss of the high voltage capacitor directly affects the operating temperature of the capacitor and can be expressed by:
Pr= Qctgδ=ωCU2tgδ·10-3
Where Pr is the active power loss of the high voltage capacitor; Qc is the reactive power of the high voltage capacitor; tgδ is the dielectric loss tangent of the high voltage capacitor; ω is the grid angular frequency; C is the permittivity of the high voltage capacitor; U is the high voltage capacitor Operating voltage.
It can be known from the formula that the active power loss and reactive power of the high voltage capacitor are proportional to the square of the operating voltage of the high voltage capacitor; as the operating voltage increases, the active power loss of the high voltage capacitor will increase rapidly, and the speed of temperature increase will also increase. The increase in freeness causes the insulation life of the capacitor to decrease. In addition, the overvoltage of the continuous operation of the high voltage capacitor is generally set to 1.10 times of the rated voltage. When the capacitor is operated under the overvoltage for a long time, the capacitor will be overcurrent and damaged; therefore, the high voltage capacitor assembly needs to be installed and perfected. Voltage protection device.
Overcurrent caused by high harmonics of the power grid
When the harmonic current in the power grid flows into the capacitor, it is superimposed on the fundamental current of the high voltage capacitor, which increases the operating current and also increases the effective value of the peak voltage on the fundamental voltage of the high voltage capacitor. If the capacitive reactance of the capacitor matches the inductive reactance of the system, the higher harmonics will be amplified to generate overcurrent and overvoltage, causing partial discharge of the insulating medium inside the capacitor, causing the capacitor to generate faults such as bulging and fuse bursts.
The busbar connected to the capacitor loses pressure
If the capacitor suddenly loses voltage during operation, it may cause the power supply side of the substation to trip instantaneously or the main transformer to open. If the capacitor is not removed when the power is turned off or the standby power is automatically put into use, it may cause the capacitor to be overloaded and damaged. In addition, when the substation loses voltage recovery without removing the capacitor, a resonant overvoltage may occur, which may damage the transformer or capacitor. Therefore, the capacitor should be equipped with a loss-of-voltage protection device to ensure reliable operation of the capacitor after the connected busbar loses voltage, and reliable access after the busbar voltage returns to normal.
Overvoltage generated by circuit breaker operation
Capacitor circuit breakers often use vacuum circuit breakers. When the circuit breaker is closed, the circuit breaker contacts may bounce and generate overvoltage. Although the resulting overvoltage peak is low, the effect on the capacitor is not large, but since the capacitor is switched over a thousand times a year, and the circuit breaker is disconnected, it may cause an overvoltage of the breakdown capacitor, so it must be taken Effective protection measures to limit the overvoltage generated by the operation of the circuit breaker.
Operating temperature is too high
As the temperature rises by 10 ° C, the capacitor capacity will decrease at a double speed; if the capacitor is operated at high electric field and high temperature for a long time, it will cause the dielectric medium to age and the dielectric loss to increase, which will cause the capacitor to heat up quickly and heat up. The life is reduced, and even the capacitor is thermally damaged and damaged. According to the regulations, if the ambient temperature exceeds 30 ° C and the capacitor case temperature exceeds 50 ° C, the ventilation device should be turned on to cool down. When the ambient temperature exceeds 40 ° C, the capacitor should be stopped immediately. Therefore, in order to prevent the capacitor from being damaged due to excessive operating temperature, a temperature monitoring device should be set to monitor the operating temperature of the capacitor at any time, and a forced ventilation device is used to improve the heat dissipation condition of the capacitor, so that the heat generated by the capacitor is convected and radiated. .
