In short. Commissioning proves that switchgear is installed correctly, safe to energise and works as designed. It runs in stages: inspection, de-energised tests, protection and control tests, energisation, and on-load checks, with every result recorded for handover.
Stages
- Documentation and inspection: drawings, certificates, nameplates, torque marks, clearances, labels, earthing, cable terminations.
- Mechanical checks: breaker racking, interlocks, spring charging, shutters, door operation.
- Electrical tests (de-energised): insulation resistance, contact resistance of joints and breaker contacts, high-voltage tests where specified, CT and VT ratio and polarity.
- Protection tests: secondary injection of every relay function, primary injection where required. See injection testing.
- Control and interlock tests: every close, trip, interlock, transfer and alarm path.
- Energisation: staged, with phase-sequence and voltage checks.
- On-load checks: current readings, temperature, load sharing, thermography.
Typical tests
| Test | What it shows |
|---|---|
| Insulation resistance | Insulation condition, moisture, contamination |
| Contact resistance | Quality of joints and breaker contacts |
| CT ratio, polarity, burden, magnetisation | Correct measurement and protection performance |
| Breaker timing | Opening and closing speed |
| Relay injection | Settings and logic operate correctly |
| Interlock checks | Unsafe operations are blocked |
| Phase sequence | Correct rotation before paralleling |
Generator-specific
- Check synchronising, load sharing and reverse power. See DG synchronising panels.
- Run load tests with load banks. See load bank testing.
- Test transfer with simulated utility failure. See commissioning service.
Handover pack
As-built drawings, test certificates, relay settings, interlock charts, spare parts list, operation and maintenance manuals, and a punch list of open items with closure dates.
Safety
Use permits, lock-out, test-before-touch and defined energisation procedures. Commissioning is a high-risk activity and should be led by competent people.
Illustrative example
During secondary injection, a relay trip output is found not wired to the breaker trip coil. The simulated trip operated the relay display only. Finding this before energisation avoided a protection that looked fine but could not open the breaker.
Commissioning sequence for switchgear
- Documents: drawings, settings, test certificates, as-built wiring.
- Visual and mechanical: alignment, torque, clearances, labelling, interlock operation.
- Insulation resistance and contact resistance of busbars and breakers.
- CT and VT tests: ratio, polarity, burden, magnetisation.
- Protection relay tests: secondary injection of every enabled function.
- Primary injection for key circuits where practical.
- Control and interlock tests including trip and close circuits and DC supply loss.
- Energisation in stages with checks of phase sequence and voltage.
- Load tests and review of thermal behaviour.
Record table
| Test | Record |
|---|---|
| Insulation resistance | Values per phase and test voltage |
| Relay function | Setting, measured pickup and time |
| Interlock | Each sequence and result |
| Trip circuit | Operation from each trip source |
Why complete testing matters
Protection that was never tested is protection that may not work. A single swapped CT lead can disable a function silently for years.
Handover
Provide final settings, test sheets, drawings and operating instructions. Train operators on interlocks and emergency procedures. See commissioning and injection testing.
Common mistakes
- Testing the relay but not the trip path to the breaker.
- No record of as-found settings.
- Energising before interlocks are proved.
What to send us
Send the equipment list and drawings. Send your application details. See also commissioning checklist.
Questions engineers ask
Why test protection if it is factory tested?
Transport, installation and wiring can introduce faults. Site tests prove the whole chain.
What is primary injection?
Passing real current through the primary circuit to check CTs, wiring and relays together.
Who should do commissioning?
Competent, authorised engineers following a written procedure.
What documents should be handed over?
Test records, settings, drawings, manuals and a punch list.
This guide gives general principles. Follow manufacturer procedures and site safety rules.