Transformers in factories and businesses can suffer failures, fires or explosions when maintenance is neglected. Repairing a damaged transformer may take considerable time. Regular maintenance is therefore important for reliable operation.
I. General inspection
- Visually inspect external, mechanical and electrical parts for discharge marks or moisture.
- Check equipment positioning, grounding and safety clearances.
- Check continuity to the main grounding system.
- Inspect transformer oil level, silica-gel breather and nameplate.
- Recheck control, alarm and temperature indication settings; the customer must provide clear, legible technical drawings.
- Check continuity of relay circuits, including thermal protection and alarms.
- Check thermostat operation, where fitted.
- Clean using a vacuum cleaner, cloth and alcohol.
- Check bolts with a torque wrench according to the manufacturer's standard or Tables 100.12 and 100.23.
II. Tests
1. Insulation resistance
Measure insulation between windings and between windings and earth. Use the manufacturer's test voltage instructions; where none are given, follow Table 100.5 referenced in the source article.
2. Transformer turns ratio
The test ratio should not differ by more than 0.5% from the adjacent winding result or calculated ratio.
3. DC winding resistance at the operating tap
Compare measurements with the manufacturer's published data. Where such data is unavailable, resistance between windings should not differ by more than 2%.
4. Oil sample breakdown voltage test
5. No-load and short-circuit tests
6. Other testing
