Abnormal analysis and fault handling of power capacitors

The power capacitor is a static reactive power compensation device whose main function is to provide reactive power to the power system. The use of local compensation reactive power can reduce the transmission current of the transmission line, and plays an important role in reducing line loss, improving power quality and improving equipment utilization.

Abnormal analysis

Overvoltage: Capacitors can be allowed to continue operating within 5% of the rated voltage, and allow short-term operation at 1.1 times rated voltage. Long-term over-voltage operation will cause the capacitor to heat up and accelerate insulation aging. Capacitors should be avoided to operate at both the highest voltage and the highest temperature.

Overcurrent: Allows operation to continue at no more than 1.3 times the rated current, but should try to eliminate long-term overvoltages and higher harmonics in the line.

Leakage oil: If the seal is not tight, impurities such as air and moisture may enter the interior, causing the internal insulation to decrease. During operation, it is found that oil leakage in the power capacitor casing, welds, etc. should be immediately withdrawn to ensure the safety of the capacitor bank.

Temperature: When the air temperature is 40 °C, the temperature of the power capacitor case must not exceed 55 °C.

2. Troubleshooting

Common malfunctions:

a, the capacitor casing expands the belly or seepage;

b. The capacitor casing is broken, and a flashover occurs;

c. The capacitor is internally short-circuited, the sound is abnormal, or the fuel is fired;

d. The temperature of the capacitor casing is higher than 55 °C, and the wax sheet is melted.

deal with:

a. When the capacitor is injecting or exploding, immediately disconnect the power supply and use a sand or dry fire extinguisher to extinguish the fire. Such accidents are mostly caused by overvoltages inside and outside the system and serious internal faults in the capacitors. Capacitors shall not be used for reclosing, and shall not be forced after tripping.

b. The switch trips, and the shunt fuse is not broken. After the capacitor is discharged for 3 minutes, check the circuit breaker, CT, cable and capacitor external. If you still can't find the problem, you should conduct an inspection test.

c. When the fuse is blown, report to the dispatcher. After obtaining the consent, open the capacitor switch. After cutting off the power supply and discharging it, perform an external inspection, such as whether there is any flashover on the outside of the casing, whether the casing is deformed, oil leakage, and whether the grounding device is short-circuited. Then use the insulation shaker to measure the pole and pole. Insulation resistance value to ground. If no fault traces are found, the fuses can be replaced and put into operation. If the fuses are blown after power transmission, the faulty capacitors should be exited and the rest of the power transmission operation should be resumed.

3. Safety issues when dealing with faults

After the switch and the knife switch are opened, the capacitor should be discharged. After the capacitor is discharged through the discharge winding, an artificial discharge should also be performed. When discharging, first connect the grounding end of the grounding wire, and discharge the capacitor several times with the grounding rod until there is no discharge spark and discharge sound, then fix the grounding end. Since the faulty capacitor may have poor lead contact, internal disconnection or fuse blown, some of the charge may not be exhausted. Therefore, the inspector should wear insulated gloves before using the faulty capacitor. The faulty capacitor is short-circuited and discharged before it can be removed.