DRY-TYPE TRANSFORMER COMPREHENSIVE MAINTENANCE PROCEDURE

DRY-TYPE TRANSFORMER COMPREHENSIVE MAINTENANCE PROCEDURE

I. SCOPE OF APPLICATION
- Dry-type transformers in operation or idle state: Routine maintenance once per year
- Dry-type transformers stored for a period awaiting commissioning: Pre-commissioning maintenance prior to energization

II. PRE-OPERATIONAL PREPARATIONS
1. Engage the backup transformer to ensure continuity of power supply.
2. Open the low-voltage (LV) side circuit breaker of the transformer to be serviced and remove the control power fuse.
3. Attach a "DO NOT CLOSE" warning sign to the switch handle.
4. Open the high-voltage (HV) side circuit breaker of the transformer to be serviced and close the earthing switch.
5. After allowing the transformer to fully discharge, lock the HV switchgear and attach a "DO NOT CLOSE" warning sign to the switch handle.

III. BODY AND VISUAL INSPECTION MAINTENANCE
1. Clean bushings and enclosure: Use a soft brush and vacuum cleaner to remove dust and dirt. Do not spray water or any liquid directly onto the transformer surface.
2. Inspect external condition: Check enclosures, gaskets, and bushings for cracks or discharge traces. Examine cables and busbars for deformation. Inspect rubber gaskets for aging. Replace any cracked or severely aged components.
3. Inspect main components: Examine winding and core surfaces for damage, corrosion, or deformation. Perform necessary repairs.

IV. ELECTRICAL CONNECTIONS AND CONTACT SURFACE MAINTENANCE
1. Inspect busbar contact surfaces: Keep surfaces clean, remove oxide layers, and apply electrical conductive grease.
2. Tighten fasteners: Inspect and tighten terminal lugs, pins, earthing screws, and connecting busbar screws. If loose, remove the screw, gently file the contact surface with a fine flat file, or replace spring washers/screws to ensure good contact.
3. Inspect wiring and electrical connections: Ensure cables, terminal boxes, and earthing wires are free from looseness or damage.

V. EARTHING AND INSULATION SYSTEM MAINTENANCE
1. Check earthing: Verify that the transformer has proper earthing. Inspect earth wires for corrosion; replace if severely corroded.
2. Measure earth resistance: Perform periodic measurement of earth resistance to ensure reliability of the earthing system. Address values that exceed the set limit promptly.
3. Check insulation: Inspect insulation layers for damage and insulators for cracks. Repair or replace any anomalies immediately.
4. Measure insulation resistance:
- Open and lock the HV side earthing switch. Use a 2500V megohmmeter to measure insulation resistance.
- Compare measurements with factory test values. Insulation resistance shall not be less than 70% of original data.
- Report immediately any不合格 results.

VI. VENTILATION, FIRE PROTECTION, AND ENVIRONMENTAL CHECKS
1. Clean ventilation system: Periodically clean or replace ventilation system filters to prevent dust accumulation that impairs cooling efficiency.
2. Check fire protection equipment: Ensure firefighting equipment in the transformer vicinity is intact and effective.
3. Clean surrounding area: Remove dust from the transformer vicinity and all auxiliary components. Maintain good ventilation.
4. Check operating environment temperature: Avoid operating in high-temperature or humid environments. Ensure adequate heat dissipation conditions.

VII. PARAMETER MONITORING AND PREVENTIVE MAINTENANCE
1. Periodically measure operating parameters: Monitor temperature, current, voltage, etc., compare with normal values, and adjust/repair any abnormalities promptly.
2. Check temperature: Regularly check transformer body and ambient temperatures to ensure normal operation.
3. Periodic testing: Measure winding voltage and insulation resistance to identify potential issues early and take corrective action.

VIII. WORK CLOSURE AND SERVICE RESTORATION
1. Close the HV side earthing switch again to discharge the transformer.
2. Inspect transformer room and transformer: Verify no tools are left behind. Confirm inventory and leave the site.
3. Reinstall the LV side circuit breaker control power fuse. Re-attach the "DO NOT CLOSE" warning sign to prevent backfeed to the transformer.
4. Open the HV side earthing switch. Re-inspect the transformer site and LV side control wiring.
5. After final confirmation, close the HV side circuit breaker to energize the transformer for trial operation. Remove the HV side warning sign.

IX. SAFETY PRECAUTIONS
- The entire maintenance process must strictly implement safety measures: de-energization, voltage verification, discharge, earthing, and signage.
- The transformer must be fully discharged both before and after insulation resistance testing.
- Dry-type transformers are oil-free. Routine maintenance does not involve oil analysis.
- Keep detailed records of all maintenance activities and establish equipment maintenance files.