Capacitor cabinet "belly"? Don't rush to change it! The power grid is "warning"!

2025-09-11 20:03:36

Those capacitors with bulges at the top are not of poor quality, but rather the "barometer" of the power grid environment. They are using deformation to tell you: the power quality here is "sick"!

The electricity bill of a certain commercial complex is unusually high, and the compensation controller is frequently burned out. During the electrical inspection, it was found that the top of many capacitors in the capacitor cabinet was severely bulging, like "little buns". After replacing the new capacitor, it bulged up again in just one month. The ultimate truth is that a certain tenant's privately added variable frequency central air conditioning produced a large amount of harmonics and became a "capacitor killer."

Why does the capacitor have a "belly"?

The root cause of the capacitor bulge is internal overheating, which causes the insulation medium to decompose and produce gas. There are two main culprits:

1. Harmonic pollution (most common): The harmonic current generated by the frequency converter and rectifier equipment flows into the capacitor, causing overcurrent heating.

2. Overvoltage operation: The system voltage is higher than the rated voltage of the capacitor for a long time (for example, the system voltage of 400V is as high as 420V), which aggravates its burden.

The cost of ignoring it: the bulging capacitor may burst and leak oil at any time, even causing phase short-circuit and fire, with extremely high risk.

Two steps for on-site quick self-examination

1. Look at the appearance (operate after power off! ): Open the capacitor cabinet regularly and use a flashlight to check if there are any bulges, oil leakage, or deformation on the top and shell of each capacitor. This is the most intuitive method.

2. Measure temperature (without power outage): Scan the capacitor shell with an infrared thermal imager or thermometer gun.The normal temperature should not exceed the ambient temperature by more than 15K (℃).If the temperature of a certain capacitor is abnormally high, it is a hidden danger point.

Treating the symptoms is more important than treating the root cause: how to eradicate it?

Changing the capacitor alone is "treating the symptoms but not the root cause," and the root cause must be found:

If you suspect harmonics, you can use an energy quality analyzer to measure the harmonic content on site (focus on 3rd, 5th, and 7th harmonics). If it exceeds the standard, an inductor should be connected in series with the capacitor circuit (e.g., a 7% inductance rate to suppress 5 or more harmonics), which is the only effective method to protect the capacitor.

If the system voltage is too high, adjust the transformer tap or choose a capacitor with a higher rated voltage (e.g., 450V) during the design phase.

summary

Goodbye bulging capacitor, don't treat it as a simple consumable replacement. It is a clear warning signal!

Action mantra:

The bulging capacitor should be replaced immediately, and the root cause should be investigated. Measure the harmonic voltage, and the series reactor is the savior.

Remember: The cost of managing capacitor bulges is much lower than the cost of increased electricity bills and equipment damage caused by poor power quality.