Capacitors are prone to four types of faults
The reactive power compensation equipment used in power systems predominantly consists of shunt compensation devices, primarily comprising shunt power capacitors, which account for over 98% of the total capacitive compensation capacity. Technical personnel must frequently inspect and patrol the power capacitors, promptly removing defective capacitors from operation to prevent accidents.
The defects that occur during the operation of capacitors are mostly oil leakage and bulging, followed by fuse failure, bursting, and even explosion accidents.
Oil leakage. If a power capacitor leaks oil, moisture and dampness will enter its interior, reducing the insulation resistance.
The oil leakage causes the oil level to drop, exposing the upper end of the lead or component above the oil surface, which can lead to discharge to the external shell or breakdown of the component. The areas where oil leaks are mostly located at the welds on the tank wall, the flange at the root of the bushing, and the cap.
Bulging. During normal operation, due to temperature rise of the capacitor and changes in ambient temperature, the shell will expand and contract as the temperature changes. However, capacitors with obvious bulging or plastic deformation of the shell should be stopped from use. This is caused by internal partial discharge, decomposition of insulating oil producing a large amount of gas, and increased internal pressure.
Explosion. The explosion of a capacitor is mainly due to the internal energy exceeding the tolerance of the casing. When the inter-electrode insulating medium breaks down, an electric arc and thermal effect are generated, causing the medium to decompose and produce gas, leading to an increase in pressure inside the box and ultimately causing an explosion. The energy for the explosion comes from the discharge current of the power system and the power capacitors connected in parallel with it. Under the long-term effect of small current faults, the energy input into the capacitor is sufficient to cause the casing to rupture.
The fuse is blown. For power capacitors with blown fuses, a visual inspection should be conducted to check for any signs of bulging, overheating, cracking, or component fusing. If there are no obvious fault characteristics on the appearance, a test should generally be conducted to measure the capacity of the power capacitor and shake-test the insulation resistance to ground. However, there have been cases where fuses were blown due to poor fuse quality, insufficient heat capacity, or poor contact, and the situation returned to normal after replacing the fuse. There are many cases of fuse blowing due to heating caused by poor contact of the fuse terminal in a single large-capacity power capacitor. For single small-capacity power capacitors, if the fuse is blown during operation and the circuit breaker does not trip, the operation can continue until too many power capacitors are removed, causing the current imbalance to exceed the allowable value. At this point, a power outage test and treatment should be carried out.