1. Overvoltage
Overvoltage is extremely harmful to power capacitors. The lifespan of power capacitors is closely related to the duration, amplitude, and frequency of overvoltage. Especially prolonged overvoltage can cause power capacitors to heat up, thereby accelerating insulation aging. Therefore, when the grid voltage exceeds 1.1 times the rated voltage of the power capacitor, it should be taken out of operation. The power frequency withstand voltage test device is suitable for withstand voltage tests of large hydro/thermal generators, using multiple reactors in parallel, and adjusting the inductance of the adjustable reactor.
2. Overcurrent
When the capacitor current exceeds 1.3 times the rated current or the three-phase unbalanced current exceeds 5%, it should be taken out of operation. Because excessive current can cause capacitor burnout accidents.
3. Oil Leakage
Power capacitors are fully sealed devices. If the seal is not tight, air, moisture, and impurities may enter the interior of the capacitor. When oil leakage occurs in the capacitor, the load should be reduced or the ambient temperature lowered, but long-term operation is not advisable. If severe oil leakage is found in the power capacitor, it should be taken out of service as soon as possible.
4. Bulging Deformation
When a fault occurs inside the capacitor tank during operation, the insulating oil is decomposed by the high temperature of the arc, producing a large amount of gas, which can cause the tank to bulge and deform. In this case, it should be immediately taken out of operation and replaced with a spare.
5. Automatic Tripping of Capacitor Circuit Breaker
After the circuit breaker trips, it must not be forcibly reclosed. At this time, first check the protection action and the relevant primary circuit, such as checking whether the capacitor has exploded, bulged, or sprayed oil. Also inspect the capacitor's circuit breaker, current transformer, voltage transformer, power cable, etc., to determine the nature of the fault. If there is no such situation, but the circuit breaker tripped due to bus voltage fluctuation caused by an external fault, a trial closing is allowed after 15 minutes. Do not attempt to reclose before the cause is identified.
6. Capacitor Shutdown Handling
In case of any of the following faults, the capacitor bank should be shut down and the duty dispatcher and department leader should be reported.
(1) Capacitor explosion;
(2) Capacitor bushing rupture with flashover discharge;
(3) Severe oil spraying or fire from the capacitor;
(4) Obvious expansion of the capacitor shell, oil leakage, or three-phase current imbalance exceeding 5%, or abnormal sounds inside the capacitor or reactor;
(5) Severe overheating of joints;
(6) Oil temperature of dense capacitors exceeding 65°C, or pressure relief valve action
