Panels and Cabinets
* Check air circuit breaker or other panels of insulation material for cracks and
cleanliness. Check condition of enclosing cabinets including hinges, latches, locks,
door gaskets, and paint.
Bushings or Insulators
Weekly Check for chipped or broken porcelain, excessive dirt film, oil level and oil or
* Clean porcelain with water, chlorothene, or other suitable cleaner. Repair chipped
spots by painting with lacquer such as red glyptal. Inspect gaskets for leaks.
Tighten bolts. Check insulation resistance with contacts closed and power factor.
Check oil sample from bottom of bushing for dielectric strength and presence of
water and dirt which may be entering at top. Replace or replenish oil if necessary.
Check and clean interior at least once every 5 years.
Bushing Current Transformers and Potential Devices
* Check tap settings and adjustments at terminal board to see that they agree with
diagrams. Check insulation resistance of wiring with devices connected. Check
ration and phase-angle adjustments of potential devices if changes have been made
in secondary connections or burden. Tighten connections, including potential device
tap into bushing.
Main Terminals and Ground Connections
Daily or Weekly Check for presence of foreign materials, birds' nests, etc. in or near
connecting buswork; loose or overheating connections; and loose or broken frame
* Tighten all bus and ground connections. Refinish joint contact surfaces if they have
been overheating. Inspect ground cable to see that it is not loose or broken.
* Remove the tanks or drain out oil so that the contacts can be inspected. Dress
contacts, if rough, with a fine file. It is necessary to remove only the projecting
beads. Pits in a flat, smooth surface are not objectionable. Check contact drop with
"ducter" or by direct-current millivolt drop. Frequency of breaker contact
maintenance should be based on number and severity of faults interrupted rather
than a definite time period. Experience will tell how many faults can be interrupted
before contact repairs are necessary. Data should be kept on each breaker to guide
future maintenance. Inspection schedules might be extended further as oil-handling
methods, methods for determining oil condition, and other improvements are made.
The following factors should be established before intervals between inspections can