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A Brief Analysis of Fault Handling Methods for Capacitors

Release time:

2024-01-05 17:26

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1. Common faults of capacitors: If any of the following conditions are detected in a capacitor, the power supply should be immediately disconnected.
(1) The capacitor casing is swollen or leaking oil.
(2) The casing has cracked, causing flashover and sparking.
(3) Abnormal sound inside the capacitor.
(4) If the shell temperature rise exceeds 55℃, the temperature-indicating strip will fall off.
2. Troubleshooting Capacitors
(1) When a capacitor explodes and catches fire, immediately disconnect the power supply and extinguish the fire using sand and a dry chemical fire extinguisher.
(2) When the fuse of a capacitor blows, you should report to the dispatch center and only open the capacitor’s circuit breaker after obtaining their approval. Before proceeding, disconnect the power supply and discharge the capacitor. First, conduct an external inspection: check whether there are any flashover marks on the bushings, whether the enclosure is deformed, whether there is oil leakage, and whether the grounding device shows any signs of short circuits. Also, measure the insulation resistance between the terminals and between each terminal and ground. Verify that the capacitor bank wiring is complete and secure, and check for any phase failures. If no faults are found, you may re-energize the capacitor after replacing the fuse. However, if the fuse continues to blow after re-energizing, you must remove the faulty capacitor and restore power to the remaining sections. If the circuit breaker trips simultaneously with the fuse blowing, do not attempt to re-energize the system forcefully. Instead, wait until the above inspections have been completed and the fuse has been replaced before attempting to re-energize the system.
(3) If the circuit breaker for the capacitor trips while the branch fuse remains intact, first discharge the capacitor for three minutes before inspecting the circuit breaker’s current transformer, power cable, and the capacitor’s exterior. If no abnormalities are found, the issue might be caused by voltage fluctuations on the busbar due to an external fault. After thorough inspection, a trial energization can be attempted; otherwise, a comprehensive energization test of the protection system should be conducted. If, after all the above inspections and tests, the cause still remains unidentified, the capacitor must be tested gradually according to established procedures. No trial energization shall be attempted until the root cause has been determined.
3. Safety precautions when handling faulty capacitors: Since the two terminals of a capacitor tend to retain residual charges, it is essential first to discharge these charges completely; otherwise, electric shock accidents may easily occur. When handling a faulty capacitor, the first step is to open the circuit breaker and the disconnect switches above and below the capacitor bank. If fuses are used for protection, remove the fuse links first. At this point, although the capacitor bank has already begun discharging through its internal discharge resistors, some residual charges will still remain. Therefore, it is imperative to perform manual discharge as well. During discharge, first securely connect the grounding end of the grounding wire to the grounding grid, then use a grounding rod to repeatedly discharge the capacitor until no sparks or discharge sounds are heard. Finally, ensure that the grounding wire is firmly secured. It should also be noted that if a capacitor has an internal open circuit, a blown fuse, or poor contact at its leads, residual charges may still remain between its two terminals. Such residual charges will not be discharged during automatic or manual discharge procedures. Hence, before coming into contact with a faulty capacitor, operating and maintenance personnel must wear insulated gloves and short-circuit the two terminals of the faulty capacitor using a shorting wire to ensure complete discharge. Additionally, for capacitors connected in series, each capacitor should be discharged individually.

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