When switchgear malfunctions, the consequences are often catastrophic. Damage to the switchgear itself can be extremely expensive, but that pales in comparison to corollary damage and the potential hazards to people. That’s why implementing an effective switchgear testing, inspection, and maintenance program is essential.
According to National Fire Protection Association (NFPA) 70B Recommended Practice for Electrical Equipment Maintenance, a switchgear assembly is assembled equipment that includes, but is not limited to, one or more of the following: switching, interrupting, control, metering, protective, or regulating devices together with their supporting structure, enclosure, conductors, electric interconnections, and accessories. They might be found outdoors as a part of a substation, or indoors as a power distribution center.
Recommended frequency of maintenance depends on environmental and operating conditions but at the least an annual inspection of the entire switchgear assembly is recommended.
The InterNational Electrical Testing Association (NETA) Maintenance Testing Specifications recommends that during these inspections the following should be performed:
- Inspect physical, electrical and mechanical condition including evidence of moisture or corona
- Inspect anchorage, alignment, grounding, and required area clearances
- Prior to cleaning the unit, perform as-found tests, if required
- Clean the unit
- Verify that fuse and/or circuit breaker sizes and types correspond to drawings and coordination study as well as to the circuit breaker’s address for microprocessor-communication packages
- Verify that current and voltage transformer ratios correspond to drawings
- Inspect bolted electrical connections for high resistance
- Confirm correct operation and sequencing of electrical and mechanical interlock systems
- Use appropriate lubrication on moving current-carrying parts and on moving and sliding surfaces
- Verify correct barrier and sutter installation and operation
- Exercise all active components
- Inspect mechanical indicating devices for correct operation
- Verify that filters are in place and/or vents are clear
- Perform visual and mechanical inspection of instrument transformers
- Inspect control power transformers for physical damage, cracked insulation, broken leads, tightness of connections, defective wiring, and overall general condition. Verify that primary and secondary fuse ratings or circuit breakers match drawings. Verify correct functioning of drawout disconnecting and grounding contacts and interlocks
- Perform as-left tests
Also during the annual inspection process, the following electrical tests should be performed:
- Resistance measurements
- Insulation-resistance tests on each bus section, phase-to-phase, and phase-to-ground
- Overpotential test on each bus section and each phase-to-ground
- Insulation-resistance tests on control wiring with respect to ground
- Electrical tests on instrument transformers
- Ground-resistance tests
- Insulation-resistance test on control power transformers
- Verify correct function of control transfer relays
- Verify operation of switchgear heaters and their controller
- System function tests
Staying on top of a switchgear maintenance program can be difficult. Maintenance is often considered a low priority and deferred or ignored until a failure occurs. However, when you fail to conduct the proper maintenance, the risk of loss is high including personnel injury or death, equipment damage, and lost production. Emerson’s electrical reliability experts can work with you to develop and implement a solid maintenance program to ensure the safety of your people and reliability of your electrical switchgear.
