Common Faults Of High-voltage Capacitor Damage

The operating voltage of the capacitor is too high

The operating voltage of high-voltage capacitors can reflect the voltage status of the substation busbar system and directly affect the lifespan and output function of capacitors. The active power loss inside high-voltage capacitors during operation is mainly composed of dielectric loss and resistance loss, and the dielectric loss accounts for more than 989% of the total active power loss of high-voltage capacitors. The dielectric loss of high-voltage capacitors directly affects the operating temperature of the capacitors, which can be represented by the following equation:

Pr=Qctg6=0CU2tg6? 10-3

In the formula, Pr represents the active power loss of the high-voltage capacitor; Qc is the reactive power of the high-voltage capacitor; US is the tangent value of the dielectric loss angle of high-voltage capacitors; 0 Is the grid angular frequency; C is the capacitance of the high-voltage capacitor; U is the operating voltage of the high-voltage capacitor.

According to the formula, the active power loss and reactive power loss of high-voltage capacitors are directly proportional to the square of the operating voltage of high-voltage capacitors. With the increase of operating voltage, the active power loss of high-voltage capacitors will rapidly increase, and the speed of temperature rise will also increase, leading to an increase in free energy and a decrease in the insulation life of capacitors? In addition, the overvoltage of high-voltage capacitors during continuous operation is generally set at 1.10 times the rated voltage. When the capacitor is operated under overvoltage for a long time, it can cause overcurrent and damage to the capacitor; Therefore, the assembly of high-voltage capacitors requires the installation of complete overvoltage protection devices.

Overcurrent caused by high-order harmonics in the power grid

When the harmonic current in the power grid flows into the capacitor, it will be added to the fundamental current of the high-voltage capacitor, causing an increase in its operating current. At the same time, it will also increase the effective value of the peak voltage on the fundamental voltage of the high-voltage capacitor. If the capacitance of the capacitor matches the system inductance, it will amplify the higher-order harmonics and produce overcurrent and overvoltage, causing partial discharge of the insulation medium inside the capacitor, resulting in bulging of the capacitor Faults such as fuse burst.

Loss of voltage on the busbar connected to the capacitor

If the capacitor suddenly loses voltage during operation, it may cause instantaneous tripping on the power side of the substation or disconnection of the main transformer. If the capacitor is not removed when the power supply is switched on or when the backup power supply is automatically put into use, it may cause overvoltage and damage to the capacitor under load. In addition, not removing capacitors when the substation loses voltage and recovers may result in resonant overvoltage, causing damage to the transformer or capacitor? Therefore, capacitors should be equipped with a voltage loss protection device to ensure reliable operation of the capacitor after the connected busbar loses voltage, and can be reliably connected after the busbar voltage returns to normal.

Overvoltage generated by circuit breaker operation

Capacitor circuit breakers often use empty circuit breakers. When the circuit breaker is closed, the contact of the circuit breaker may bounce and generate overvoltage. Although the resulting overvoltage peak is low and has little impact on the capacitor, the annual switching frequency of the capacitor is more than a thousand times, and the circuit breaker may cause overvoltage to breakdown the capacitor when it is opened. Therefore, Effective protective measures must be taken to limit the overvoltage generated by circuit breaker operation

Operating temperature too high

Due to a temperature increase of 101C, the rate of capacitor capacitance decrease will double. If the capacitor is operated under high electric field and high temperature for a long time, it will cause insulation medium aging and increased dielectric loss, leading to rapid heating and heating inside the capacitor. This will reduce the lifespan of the capacitor and even cause thermal breakdown and damage. According to regulations, if the ambient temperature exceeds 301C, the temperature of the capacitor shell will exceed 501C, Ventilation devices should be turned on to cool down. When the ambient temperature exceeds 401C, the operation of the capacitor should be immediately stopped. Therefore, in order to prevent damage to capacitors due to high operating temperatures, temperature monitoring devices should be installed to monitor and control the operating temperature of the capacitors at any time, and forced ventilation devices should be used to improve the heat dissipation conditions of the capacitors. The heat generated by the capacitors should be dissipated through convection and radiation.