An inspection analysis of the physical condition of a plant’s distribution system can be utilized (hopefully on a continual basis) to improve plant reliability. The following inspection requires little, if any, capital investment while providing a favorable increase in reliability:
a) Equipment should be periodically checked for proper condition, and programs should be initiated for preventive maintenance procedures as required.
1) Oil in transformers and circuit breakers should be periodically checked for mineral, carbon, and water content as well as level and temperature.
2) Molded case circuit breakers should be exercised periodically (that is, operated “on” to “off” to “on”).
3) Terminals should be tightened. Each terminal should be inspected for discoloration (overheating), which is generally caused by either a bad connection or equipment overload. Cabinets, etc., should be checked for excessive warmth. Remember that circuit breakers and fuses interrupt as a result of heat in the overload mode.
4) Surge arresters should be checked for their readiness to operate.
b) Distribution centers should be checked to see that spare fuses are available. Spare circuit breakers may also be necessary for odd sizes or special applications.
c) Switches, disconnect switches, bus work, and grounds should be checked for corrosion, and unintentional entry of water or corrosive foreign material. It may be wise to operate suspected switches to see that their mechanisms are free, so that faults can be properly isolated and switches safely re-fused.
d) The mechanical part of the electrical system should be checked.
1) The conduit, duct, cable tray, and busway systems should be well supported mechanically, and the grounding system should be electrically continuous. Employees can be shocked or injured if a circuit faults to ground without a solid continuous return path to the source interrupter.
Supports, such as wood poles, should be checked for excessive rusting or rotting, which would significantly reduce their mechanical strength.
2) Open wire circuits should be checked for insulator and surge arrester failure and contamination.
3) The system’s key locations (open area distribution centers and lines) should be checked for foreign growth, such as trees, weeds, shrubs, etc., as well as for general accessibility. The distribution centers should be free from storage of trash, flammables, or even general plant inventory.
4) Permanent and portable wiring should be checked for fraying or other loss of insulating value.
5) In general, the system should be checked for any obvious situations where accidents could precipitate an interruption.
e) The electrical supply room(s) should be thoroughly checked.
1) The relay and control power fuses should be intact (not blown).
2) All indicating lights should be operable and clearly visible.
3) All targets should be reset so that none show a tripping. Counters (if any) should be checked and the count (number) should be recorded.
4) The control power, batteries, emergency lighting, and emergency generation should be tested and checked to see that they are operational. In many cases, plants have been unable to transfer to their spare circuit or start their standby generator because of dead batteries.