IMPORTANCE OF CHECKS AND MAINTENANCE
Installed in clean, well ventilated or air-conditioned locations, switchgear will require little routine maintenance. Major inspection should be scheduled for power plant shutdowns and concentrate for low voltage switchboards on identifying contact wear, correct operation of interlocks, correct overload settings and fuse sizes, signs of overheating, and undue dirt or corrosion.
For MV switchgear similar considerations apply although more extensive checks on protective devices, circuit breaker oil, vacuum bottle contact distances are required as specified by the Manufacturer.
Exceptions to the above rule are devices which operate frequently, where inspection/overhaul may need to be based on the number of operations. Also, MV isolating devices which have cleared a short circuit will require confirmation that the insulating medium and the circuit contacts are fit for continued service.
Gas Insulated Switchgear (GIS) shall be maintained in accordance with the manufacturer’s recommendations. Where extensive (intrusive) maintenance is required, the Manufacturer is involved in the activity.
For older switchgear, a condition assessment should be performed to establish that the equipment remains in a suitable condition for further service.
Partial discharge testing and infrared scanning can be used to obtain data on the performance of the insulation system and the integrity of the switchgear busbars and cable terminations. The frequency of such tests will depend on the duty, age and condition of the switchgear.
The effectiveness of infra-red scanning depends on the ability to access the current-carrying components under loaded condition. Scanning through metallic enclosures has generally proved ineffective. Removal of enclosures of live equipment may not be possible without compromising electrical safety.
INSPECTION
- General external condition.
- Cable boxes internal.
- Circuit breakers internal.
- Fused contactors internal.
- Busbar compartments internal.
- Metering:
- Correctness main voltmeters.
- Correctness main ammeters.
- Correctness of other measuring systems.
- General internal condition of outdoor equipment.
TEST AND MEASUREMENT
CIRCUIT BREAKERS IN/OUTGOING AND FUSED CONTACTORS:
- Operating mechanism.
- Draw-out system/interlocks.
- Control equipment.
- Insulation resistance
- Dielectric strength across open contacts.
- Ductor test across closed contacts.
- Electrical protection/tripping.
- Certified Ex’e’ thermal protection.
- Contact distance.
- Dielectric test oil.
- Insulation resistance of cable (incl. motor if applicable).
- Restart system.
BUSBAR SYSTEMS
- Torque bolts.
- Insulation resistance.
- Dielectric strength.
- Continuity (ductor).
- Correctness of kW, kVAr, max. demand of measuring systems.