A capacitor is a silent piece of equipment with no moving parts and no circulating oil — which tempts neglect. But its importance in power factor improvement and the danger of its stored energy demand a disciplined periodic maintenance program, starting above all with the golden discharge rule.
Periodic Maintenance Checklist
- Cleanliness: ensure the capacitor body and its insulators are free of dust, dirt, and bird droppings — surface contamination on insulators is a path for surface leakage.
- Stability: check that the capacitor has not shifted or loosened due to wind and weather.
- Paint: integrity of the body's metal coating against scratches and rust — rust is a gateway to tank corrosion.
- Nameplate: verify its data remains legible, as it fades over time and you lose the unit's reference data.
- Insulators: clean the bushings — which are the same type used on transformers — and check for cracks.
- Connections: tightness of connection and joint points to prevent looseness, and inspect them with thermal imaging under load.
- Earthing: check the connection points at the earthing point between the capacitor body and ground.
- Listening: confirm the absence of abnormal sounds (buzzing, crackling) for any reason.
- Control cabinet: verify it is closed, if present, so birds and rodents cannot get in.
- Visual inspection of units: bulging of a unit's casing or leakage of its dielectric fluid = replacement, not monitoring.
The Golden Rule Before Any Contact
Disconnecting the electrical source does not mean the electricity is gone from the capacitor — its very function is to store energy! You must wait for the discharge time, then manually discharge and earth it before touching it, and avoid any contact between the capacitor's terminals that could cause a harmful discharge. Full details in Capacitor Discharge and Safety Precautions.
Indicators Requiring Immediate Action
- A bulging unit or leaking dielectric — immediate replacement.
- Repeated fuse blowing at the same location — investigate, don't just replace the fuse.
- Operation of unbalance protection — a comprehensive inspection of the bank's units before restarting.
Sample answer: Among the most important: cleaning the body and insulators of dust and bird droppings, checking the capacitor's stability and that it has not loosened due to weather, ensuring the connection and joint points are tight, checking the earthing connection between the body and ground, and verifying the legibility of the nameplate, the integrity of the metal paint, the absence of abnormal sounds, and the absence of bulging in the units. Before any direct work: discharging the stored energy and earthing — since a capacitor retains its charge after the source is disconnected.
Starting to remove connections immediately after disconnecting the bank from the source. The stored charge remains and can be lethal — discharge time, then verification, manual discharge, and earthing, then work.
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