Transport damage, incorrect settings and document mismatches should be found before voltage is applied. This checklist helps organize that review, but it does not replace the project commissioning procedure, manufacturer instructions, local safety rules or authorization by the responsible electrical engineer.
1. Establish the release basis
Verify the drawing revision before work begins. Any connection made to an obsolete drawing must be rechecked against the approved revision.
2. Check delivery and storage condition
- Serial number, shipping marks and packing list agree.
- Shock or tilt indicators, where specified, have been reviewed.
- Packaging shows no impact or moisture damage.
- Loose accessories are identified and complete.
- Bushings, terminals, enclosure panels and lifting points are undamaged.
- Transport braces and temporary covers are identified.
- Storage and preservation met manufacturer requirements.
Liquid-filled units
Check for leakage, damaged gasket joints, abnormal oil level, valve status, breather/conservator condition and traceability of any separately shipped oil, radiators or bushings.
Dry-type units
Confirm windings and insulation are dry, clean and undamaged; ventilation passages contain no foreign material; and enclosure panels, screens and storage-heating provisions are complete.
3. Verify mechanical installation
Do not block radiator airflow or dry-type ventilation openings with walls, cables or stored material.
4. Confirm earthing and bonding
Verify the tank or enclosure, designated earth terminals, neutral, cable screens, armour, marshalling box, doors and removable panels against the approved earthing design. Record conductor size, route, joint condition and site earth-test evidence.
5. Check HV and LV connections
- Confirm cable identity, phase designation and phase sequence.
- Match transformer terminal markings to the winding diagram.
- Verify cable type, conductor size, insulation level and termination kit.
- Maintain bending radius, support, clearances and creepage distance.
- Prepare contact surfaces and tighten joints using the approved method.
- Ensure flexible connections do not impose excessive bushing force.
- Complete gland, sealing, stress-control, barrier and joint records.
6. Verify tap position and ratio
Confirm whether the tap changer is off-circuit or on-load; record physical and indicated position; verify local and remote indication; review ratio-test results; and ensure corresponding phase taps agree. An off-circuit tap changer must not be operated while energized.
7. Prove accessories and auxiliaries
| Area | Typical checks |
|---|---|
| Liquid-filled unit | Oil level, temperature, pressure relief, gas relay, breather, valves, fans and pumps as fitted. |
| Dry-type unit | Winding sensors, temperature controller, fans, heaters, enclosure interlocks as fitted. |
| All units | Auxiliary supply, fuses, terminal blocks, alarms, trips, communications, local/remote selection and sealed entries. |
Functional testing should use the approved schematic and prove both local indication and the intended remote response.
8. Review protection readiness
Current-transformer secondary circuits must not be left open while primary current flows. Follow the approved CT safety procedure.
9. Complete the approved site tests
The exact programme and limits come from the standard, manufacturer and project procedure. Depending on scope, it may include insulation resistance, winding resistance, ratio/polarity/vector group, phase sequence, oil quality, cable/busbar tests, functional tests, protection injection and comparison with factory baseline results.
Do not copy test voltages or acceptance values from another transformer. The equipment, connection method, temperature and safety controls must suit the exact unit.
10. Construction-specific readiness
Liquid-filled transformer
Confirm oil processing records, correct oil level, absence of leaks, service valve positions, breather condition, release of trapped air only as instructed, removal/reset of transport restraints, acceptable oil results and the intended cooling configuration.
Dry-type transformer
Confirm clean and dry coils, removal of loose material and shipping supports as instructed, unchanged clearances, correctly connected sensors, fan operation, approved enclosure ventilation and suitable room airflow.
11. Final walkdown and authorization
Account for personnel; close permits; remove tools, test leads and loose material.
Control temporary earths, covers, barriers, doors, tap position and downstream circuit state under the switching programme.
Approved settings, trip circuit, control power, interlocks and SCADA status must be healthy.
Assess every punch item and document any formal acceptance.
The designated responsible person signs the energization release.
12. Observe first energization
The approved plan should define observation time and measurements. Watch for abnormal sound, vibration, smell, discharge indication, leakage, pressure, temperature, phase voltage/sequence, neutral current, alarms, cooling operation and secondary voltage at the selected tap.
Hold-point summary
| Hold point | Ready when | Evidence |
|---|---|---|
| Documents | Drawings, procedures and settings are approved. | Document register |
| Delivery | No unresolved damage or preservation issue. | Receipt inspection |
| Installation | Mechanical, cooling and access requirements are accepted. | Installation checklist |
| Connections | Power, earth and auxiliary connections are complete. | Joint and test records |
| Protection | Settings, CT circuits and trip paths are proven. | Protection report |
| Release | People, tools, temporary connections and open items are controlled. | Signed release |