Abnormal phenomena and fault handling during capacitor operation

Leakage oil

Due to improper handling methods, the porcelain casing is pulled, causing cracks in the flange weld, or the force of tightening the nut during wiring is too large, causing damage to the weld of the porcelain sleeve and some defects in the manufacturing process. The capacitor is leaking. At the same time, since the temperature changes drastically after the capacitor is put into operation, the internal pressure increases, which makes the oil leakage phenomenon more serious. In addition, due to long-term operation, the coating of the capacitor casing may be peeled off, and the iron corrosion is also a cause of leakage of the capacitor during operation.

The consequence of leakage of the capacitor is that the impregnating agent is reduced, the upper part of the component is easily wetted and penetrated to damage the capacitor, so repairs must be made in time.

2. Shell expansion

Since the internal medium of the capacitor is freed by the voltage, the medium is decomposed to precipitate a gas or the dielectric is precipitated due to the breakdown of some components and the discharge of the pole to the outer casing. These gases will cause an increase in pressure in the sealed outer casing, thus causing the outer casing to expand. Therefore, capacitor casing expansion is a sign of a capacitor failure or failure. If the capacitor casing is found to be inflated during the operation, measures should be taken in time. If the expansion is serious, stop using it immediately to avoid accidents.

3. Capacitor explosion

When an interpolar or pole-to-case breakdown occurs inside the capacitor, the capacitor bank operating in parallel with it will discharge it, at which point the capacitor may blast due to extreme energy. Since the inside of the low-voltage capacitor is generally equipped with a component protection fuse, such an accident occurs mostly in a high-voltage capacitor bank in which internal component protection is not installed. The consequences of capacitor blasting can jeopardize other electrical equipment and even cause a fire in the capacitor room (cabinet). In order to prevent the blasting accident of the capacitor, in addition to the requirement to strengthen the patrol inspection in operation, the most important time is to install the protection device of the internal components of the capacitor, so that the capacitor is cut off from the power grid in time before the explosion accident occurs.

4. The temperature is too high

Due to the poor design and installation of the capacitor chamber (cabinet), the ventilation conditions are poor, the capacitor bank has long-term over-voltage operation, and the capacitors are over-current due to the influence of high-order harmonic currents caused by nearby rectifying components. The temperature rises. In addition, due to the aging of the capacitor after long-term operation of the capacitor, the dielectric loss (tgδ) is continuously increased, and the temperature rise of the capacitor may be too high. Capacitors operating for longer than the specified temperature will seriously affect their service life and cause damage to the capacitor due to accidents such as insulation breakdown.

Therefore, the ambient temperature should be strictly monitored and controlled during operation and measures should be taken to prevent it from exceeding the allowable temperature rise. If the specified allowable temperature rise is still exceeded after taking measures, the capacitor bank should be stopped.

During the summer operation, the on-duty personnel must open the low-pressure chamber exhaust fan in time according to the inspection and temperature conditions to reduce the temperature of the low-pressure chamber to facilitate the operation of the capacitor bank.

5. Porcelain insulation surface flashover

Due to the lack of cleaning and maintenance of the capacitor during operation, the porcelain insulating surface may cause discharge due to contamination. In areas with serious pollution, especially in bad weather conditions (such as wind, rain, snow, thunder, etc.), or in the case of various internal and external overvoltages and system resonances, the porcelain insulation surface can cause flashover accidents. Causes damage to the capacitor and tripping of the switch. Therefore, regular cleaning inspection should be carried out on the capacitor bank in operation, and other appropriate measures should be taken in areas with serious pollution.

6. Abnormal noise

The capacitor should not emit a special noise during operation. If there is a "sniff" or "click" sound during operation, there is a partial discharge phenomenon externally or internally. The “click” sound is a precursor to the internal insulation breakdown of the capacitor, so it must be stopped immediately to find the faulty capacitor.

When handling a faulty capacitor, first open the switch of the capacitor and the upper and lower switches. If fuse control and protection are used, the fuse tube should be removed. At this time, although the capacitor bank has self-discharged through the discharge resistor, there is still some residual charge, so manual discharge must be performed. When discharging, first connect the grounding end of the temporary grounding wire to the grounding grid, and then discharge the capacitor several times with the grounding rod until there is no cremation and no discharge. Finally, connect the ground wire to the capacitor busbar firmly.

Special attention should also be paid to the faulty capacitor itself, which may also have residual charge between the two poles. This is because the faulty capacitor may be internally broken or fuse blown, or it may be poor lead contact, so that its residual charge will not be discharged during automatic or manual discharge. Therefore, the operating or maintenance personnel should also bring the insulating gloves before touching the faulty capacitors, short the two poles of the faulty capacitor with a short-circuit wire, and discharge them before starting the disassembly. In addition, capacitors connected in series should also be discharged separately. In short, because the two poles of the capacitor have the characteristics of residual charge, it is necessary to exhaust the charge from various aspects, otherwise an electric shock accident is likely to occur.