RokBench · Maintenance checklist
Transformer
Dry-type, 600 V class. Dry-type and liquid-filled power and distribution transformers.
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De-energize, verify absence of voltage and apply lockout/tagout before any work inside equipment (NFPA 70E). Compare every measured value with the manufacturer's data, the referenced tables and the equipment's own history. This checklist contains no pass/fail values.
Inspection
| ✓ | Item | Instrument | Measured / observed | Notes |
|---|---|---|---|---|
| Compare nameplate data with the drawings and the protective device settings. See: Single-line diagram · Coordination study | — | |||
| Inspect enclosure, ventilation openings and cooling fans for blockage, dust, moisture and signs of overheating. Field tip: Discolored insulation or a burnt smell near a connection usually points to a loose joint, not a winding problem. See: NFPA 70B (2023), transformer maintenance chapter · Manufacturer's instructions | — | |||
| Perform an infrared survey of terminations and the enclosure under load before shutdown. Field tip: Scan with the load as high as practical and record the load at the time of the survey. See: ANSI/NETA MTS Section 9 (thermographic survey) · NFPA 70B (2023), thermography | Thermographic camera | |||
| Verify grounding of the enclosure, core (where accessible) and neutral per the drawings. See: NEC 2023 450.10, 250.30 · Drawings | — |
Electrical Test
| ✓ | Item | Instrument | Measured / observed | Notes |
|---|---|---|---|---|
| Insulation resistance: winding to winding and each winding to ground. Field tip: Record insulation temperature and correct readings to a common reference before trending. See: Compare against ANSI/NETA MTS Table 100.1 and the equipment test history · RokBench: IR temperature correction | Insulation resistance tester 1 kV class | |||
| Turns ratio on every tap position in service, compared with nameplate and previous results. See: ANSI/NETA MTS 7.2.1 / 7.2.2 · IEEE Std C57.12.90 | Transformer turns ratio (TTR) test set | |||
| Winding resistance on each winding and tap in service. Field tip: Demagnetize the core after DC winding tests if the manufacturer recommends it. See: ANSI/NETA MTS 7.2.1 / 7.2.2 · IEEE Std C57.152 | Winding resistance meter (DC) |
Mechanical Check
| ✓ | Item | Instrument | Measured / observed | Notes |
|---|---|---|---|---|
| Check bolted connections at terminals and bus links. See: Torque to the manufacturer's values (ANSI/NETA MTS Table 100.12 where none are published) | Calibrated torque wrench or low-resistance ohmmeter | |||
| Verify tap changer position matches the design setting and the mechanism operates freely (de-energized tap changer). See: Manufacturer's instructions · Drawings | — | |||
| Clean insulators, windings and enclosure with methods approved by the manufacturer. See: Manufacturer's instructions | — |
Functional Check
| ✓ | Item | Instrument | Measured / observed | Notes |
|---|---|---|---|---|
| Test temperature alarms and trips, fan controls and any sudden-pressure or gas relay by simulation. See: Manufacturer's instructions · Control schematics | — | |||
| After re-energizing, verify secondary voltage and phase rotation. See: Drawings | Multimeter and phase rotation meter CAT III or IV for the location |
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| Technician signature | |
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RokBench is a screening tool intended to assist qualified engineers. It does not constitute engineering services, does not produce sealed or certified deliverables, and does not replace applicable codes, standards, manufacturer documentation, or the judgment of a licensed professional responsible for the design. Verify all results independently before use. Pointers refer to NFPA 70B, ANSI/NETA MTS and IEEE documents as published by their owners; verify against the edition in use.