Abnormal phenomena and faults of power capacitor and matters to be observed in handling accidents

(1) Oil leakage

Due to improper handling method, or lifting the porcelain bushing, cracks are produced at the welding joint of the injection flange. When wiring, the welding joint of the porcelain bushing is damaged due to excessive screw force, and some defects in the product manufacturing process may cause leakage and oil leakage of the capacitor. At the same time, due to the drastic temperature change after the capacitor is put into operation, the increase of internal pressure will cause leakage In addition, after a long time of operation, the paint layer of the capacitor shell may peel off and the iron sheet may be rusted, which is also a reason for the leakage of the capacitor in operation. The consequence of the leakage of the capacitor is that the impregnant is reduced, and the upper part of the component is prone to moisture and breakdown, which will damage the capacitor. Therefore, it must be dealt with in time.

(2) Shell expansion

Due to the dissociation of the dielectric in the power capacitor under the action of voltage, the dielectric will decompose and release gas, or due to the breakdown of some components and the discharge of the electrode to the shell, the dielectric will release gas. In the sealed shell, these gases will cause the increase of pressure, which will cause the expansion of the shell. Therefore, the expansion of the capacitor shell is a symptom of the capacitor failure or before the failure. In the process of operation, if it is found that the capacitor shell expands, measures should be taken in time. If the expansion is serious, it should be stopped immediately to avoid the expansion of the accident.

(3) Electric passenger explosion

When the internal components of the capacitor break down from pole to pole or from pole to shell, other capacitors in parallel will discharge it. At this time, due to the great energy released, it may be suitable for the capacitor explosion. Because the low-voltage capacitor is generally equipped with the component protection fuse inside, this kind of accident often occurs in the high-voltage capacitor bank without the internal component protection, It may endanger other electrical equipment, and even cause fire in the capacitor room. In order to prevent the explosion accident of the capacitor, in addition to strengthening the inspection in operation, the most important thing is to install the protective device of the internal components of the capacitor, and remove the capacitor in time before the explosion accident.

(4) High temperature rise

Due to the unreasonable design and installation of the capacitor room, poor ventilation conditions, long-time over-voltage operation of the capacitor and the influence of high-order harmonic current caused by the nearby rectifying device, the capacitor over-current can make the capacitor exceed the allowable temperature rise. In addition, due to the dielectric aging after the long-term operation of the capacitor, the increasing dielectric loss ('rd) may also make the capacitor temperature rise The temperature rise of the container is too high. Long term operation of capacitor beyond the specified temperature will seriously affect its service life, and lead to insulation breakdown and other accidents, which will damage the capacitor. Therefore, in operation, its environmental temperature should be strictly monitored and controlled, and measures should be taken to make it not exceed the allowable temperature rise. For those who still exceed the allowable temperature rise after taking measures. We should stop the dangerous traffic.

(5) Flashover of porcelain insulation surface

In operation, the capacitor may discharge due to its lack of cleaning and maintenance. The ceramic insulation surface may cause discharge due to pollution. In the area with serious pollution, especially in the case of severe weather conditions (such as rain pouring snow), or in case of various internal and external overvoltage. It can cause pollution flashover accident on the surface of porcelain insulation, damage of capacitor and trip of circuit breaker. Therefore, the capacitor in operation is the Bank of the capacitor, and it should be cleaned and inspected regularly. In the area with serious pollution, other anti pollution construction shall be taken.

(6) Abnormal sound

There should be no special noise during the operation of capacitor. If it is running. If it is found that there is a "squeak" or "coo" sound, it means that there is partial discharge outside or inside. It is the precursor of the internal insulation collapse of the capacitor. Therefore, the operation should be stopped to find the fault capacitor. When dealing with the fault power capacitor, the circuit breaker of the capacitor bank and its upper and lower isolating switches should be opened first. If the fuse protection is adopted, the fuse tube should be removed At this time, although the capacitor bank has discharged by itself through the discharge resistance, there will still be some residual charges, which must be artificially discharged. When discharging, the grounding terminal of the grounding wire should be fixed with the grounding grid, and then the grounding baseball should be used to power the capacitor for many times until there is no spark and discharge sound. Finally, the grounding wire should be fixed

It should also be noted that if the capacitor is internally broken, the fuse is blown or the lead is in poor contact, there may be residual charge between the two poles. In this way, the residual charge will not be discharged during automatic discharge or manual discharge. Therefore, before contacting the faulty capacitor, the operation or maintenance personnel should also wear insulating gloves and use a short line to short the two poles of the faulty capacitor to discharge it. In addition, capacitors connected in series should also be discharged separately.

In a word, because the two poles of capacitor have the characteristic of residual charge. Therefore, we must try to discharge its charge, otherwise it is easy to get electric shock.