Maintenance Tips for Dry-Type Power Transformers

Part 1: Working Principle of Transformers

In electrical equipment and wireless communication circuits, transformers are commonly used to step up/down operating voltages, match characteristic impedances, and provide isolation protection. In generator sets, an electromotive force can be induced in coils whether coils move through magnetic fields or magnetic fields move past stationary coils. In both scenarios, the magnitude of magnetic flux remains unchanged, yet the total flux linked with the coils varies — this forms the fundamental principle of mutual induction. A transformer is a component that utilizes electromagnetic mutual induction to convert voltage, current and characteristic impedance.

Part 2: Maintenance Practices to Extend the Service Life of Dry-Type Power Transformers

1. Switch to the standby transformer, disconnect the low-voltage circuit breaker of the transformer under maintenance, remove the operating fuse of the control power supply, and hang a "No Closing Operation" warning sign on the cabinet door handle.

2. Disconnect the high-voltage circuit breaker of the transformer under maintenance, close the earthing switch, fully discharge the transformer, lock the high-voltage cabinet, and hang a "No Closing Operation" warning sign on the cabinet door handle.

3. For dry-type transformer maintenance: first clean the porcelain bushings and cabinet housing. Next, inspect the cabinet housing, gaskets and porcelain bushings for cracks or discharge marks, check if rubber pads are aged, and examine cables and busbars for deformation. Replace any damaged components with cracks.

4. Inspect the busbar surfaces to ensure they are clean. Remove oxide layers on surfaces and coat with electrical compound grease.

5. Verify reliable transformer earthing; check if earthing wires are corroded, and replace severely corroded wires.

6. Tighten lead terminals, pins, earthing bolts and busbar connecting bolts. For loose connections, remove the bolts, lightly file contact surfaces with a flat fine file, or replace spring washers and bolts until sound electrical contact is achieved.

7. Clean dust from the transformer periphery and accessories, and inspect the integrity of fire-fighting equipment and ventilation systems.

8. Open the high-voltage earthing switch and lock the high-voltage switch cabinet. Measure insulation resistance with a 2500V megohmmeter, then compare readings with factory test values. The measured insulation resistance shall not be lower than 70% of the original factory record. Report non-compliant results for immediate rectification.

9. Close the high-voltage earthing switch again to discharge the transformer.

10. Check the transformer room and transformer body for leftover tools, then evacuate the work site.

11. Reinstall the operating fuse for the low-voltage circuit breaker control power supply, and rehang the "No Closing Operation" warning sign to prevent reverse power feed to the transformer.

12. Open the high-voltage earthing switch, re-inspect the transformer site and low-voltage control wiring. After confirming no abnormalities, close the transformer high-voltage circuit breaker for trial operation, then remove the warning sign on the high-voltage cabinet.

13. Complete maintenance and trial operation records.