In short. Protection can fail silently, so it has to be tested on a schedule. A lifecycle plan covers breakers, relays, instrument transformers, DC systems and connections, with intervals based on manufacturer advice, duty and site risk, and records that show trends.
Maintenance activities
| Item | Activities |
|---|---|
| Breakers | Clean, lubricate, check mechanisms, operate, measure timing and contact resistance, replace worn parts |
| Relays | Settings check, secondary injection, trip path test, firmware record |
| CTs and VTs | Visual checks, insulation, burden, ratio where indicated |
| Busbars and joints | Torque checks, cleaning, thermography. See thermal engineering |
| DC system | Battery load tests, charger checks, earth-fault checks. See DC systems |
| Interlocks | Function tests |
| Earthing | Continuity and resistance tests |
| Generator protection | Reverse power, voltage and frequency checks |
Approaches
- Time-based: fixed intervals according to manufacturers and standards.
- Condition-based: use measurements and diagnostics, such as breaker operation counts, contact wear, partial discharge and temperature.
- Risk-based: more frequent maintenance for critical or harsh-environment equipment.
Record keeping
Keep as-found and as-left data, settings, test results and defects. Trends reveal deterioration, for example rising contact resistance or increasing breaker operating time.
Operating the unused
Breakers and mechanisms that rarely operate can stick. Scheduled operation exercises them. Generators’ protection should be tested under real conditions where practical, since a protection never operated is not proven.
End-of-life planning
- Watch for obsolete relays, unsupported firmware and unavailable spares.
- Track breaker operations against rated life.
- Plan replacement or retrofit before failure. See legacy modernisation.
- Maintain critical spares.
Illustrative example
An annual maintenance programme includes thermography under load, which finds a hot joint at a breaker. The joint is retightened and cleaned during a planned outage. Records show contact resistance on one breaker rising year over year, so it is scheduled for overhaul before it fails. See also annual maintenance contracts.
A lifecycle test plan
| Interval (typical) | Activity |
|---|---|
| Monthly | Visual check, alarms review, DC supply and charger status |
| Annually | Thermography, breaker exercise, operation check, cleaning |
| Every 2 to 5 years | Relay functional testing, trip-time tests, insulation and contact resistance |
| As needed | After a trip, fault or settings change |
Set intervals using the maker’s guidance and the criticality of the site.
Condition indicators
- Breaker operation count and time.
- Contact wear and resistance.
- Trip-coil and spring-charge motor condition.
- Battery capacity trend.
- Hot spots on thermal images.
Why lifecycle testing matters
Rarely operated breakers can stick through lubricant ageing and dust. A breaker that has not moved in years may not open when needed, so periodic exercise matters.
Records and trending
Keep a history for each device so changes are visible. Compare results with the baseline from commissioning.
Spares and obsolescence
Identify devices near end-of-support and plan replacement or retrofit. See legacy modernisation and preventive maintenance.
Common mistakes
- Testing relays but never operating breakers.
- No record of changes.
- Skipping outages because the plant is busy.
What to send us
Send equipment lists and maintenance history. Send your application details. See also preventive maintenance.
Questions engineers ask
How often should protection be tested?
Follow manufacturer guidance and site policy, with shorter intervals for critical or harsh sites.
Do I need to shut down to test?
Many tests need an outage. Plan them, or design redundancy so tests can be done without losing supply.
What is condition-based maintenance?
Maintenance triggered by measured condition rather than a fixed calendar.
When should I replace a relay?
When it is obsolete, unreliable or lacks needed functions, ideally before failure.
This guide gives general principles. Intervals should follow manufacturer and regulatory advice.