I. Daily Maintenance (conducted daily/weekly)

• Check the transformer body, bushings, and cooling system for damage, oil leakage, or seepage (focus on tank welds, valves, gaskets, etc.).
• Observe whether the surface of porcelain bushings is clean and free of cracks, damage, or discharge marks (such as creepage, which may cause insulation breakdown).
• Check if the oil level in the tank and conservator is within the normal range (the oil level gauge scale should match the ambient temperature; a too-low level may indicate oil shortage, and a too-high level may cause oil spray).
• Check the temperature displayed by the oil temperature gauge (or thermostat) to ensure it does not exceed the rated value (generally, the top oil temperature ≤ 85℃, with slight differences for different models).

• Listen to the transformer's operating sound: normally, it is a uniform "buzzing" electromagnetic sound. If there are abnormal noises (such as "cracking" discharge sounds or "gurgling" bubbling sounds), internal faults may occur.
• Inspect the cooling system: check if fans and oil pumps are operating normally (for air-cooled/forced oil-air cooled types) and if radiators are blocked or dusty.
• Check the breather: observe if the silica gel color is normal (blue when dry, turning pink or white when damp). If dampness exceeds 1/2, replace it.
• Inspect the grounding device: ensure the shell and neutral point grounding are firm, without looseness or rust.

II. Regular Overhaul (conducted monthly/quarterly/annually, with cycles adjusted based on capacity and operating environment)

1. Monthly/Quarterly Overhaul

• Oil Quality Inspection: Take a small amount of oil sample for observation. Normally, it should be transparent and light yellow. If it is turbid, black, or contains impurities, further testing (for moisture, dielectric loss, breakdown voltage, etc.) is required.
• Accessory Function Testing:
  • Tap Changer: Manually/electrically switch gears to check flexibility and accuracy of gear indication (to avoid overheating due to poor contact).
  • Protection Devices: Test the operational reliability of gas relays, pressure relief valves, and thermostats (such as light gas alarm and heavy gas tripping functions of gas relays).
• Cleaning and Fastening: Remove dust and oil stains from the surface of bushings and radiators; check if terminal blocks and bolts are loose and if there are signs of overheating and oxidation (use an infrared thermometer for detection).

2. Annual Overhaul (or every 2-3 years, combined with preventive tests)

• Oil Quality Testing: Entrust professional institutions to conduct a full analysis, including moisture content, acid value, dielectric loss, flash point, breakdown voltage, etc. If indicators exceed standards, oil filtering or oil replacement is required.
• Insulation Inspection:
  • Measure the winding insulation resistance and absorption ratio (using a megohmmeter) to judge the degree of insulation aging (for transformers of 35kV and above, the insulation resistance at room temperature is generally ≥ 3000MΩ).
  • Check if the iron core grounding is good and measure the grounding current (should be ≤ 0.1A to avoid eddy current overheating due to multi-point grounding).
• In-depth Maintenance of Cooling System: Clean radiators and cooler pipes to clear blockages; replace fan bearings and oil pump seals, and add lubricating oil.
• Tap Changer Overhaul: Lift out the switch core, clean contacts, check wear, apply special grease; measure the contact resistance of each gear (should be ≤ 50μΩ).

III. Special Maintenance (for abnormal conditions or long-term idle equipment)

• In case of gas relay operation, short-circuit faults, etc., disassemble and inspect windings, iron cores, and leads for deformation or burnout; test dissolved gases in oil (such as acetylene and hydrogen content to determine if there is internal arc discharge or overheating).
• After repair, re-conduct insulation tests, no-load tests, and load tests, and put into operation only after passing.

• Regularly (every 15 days) start the cooling system to run for 10-15 minutes to prevent component rust.
• Maintain normal oil level, seal bushings and valves tightly to prevent moisture intrusion; if the ambient humidity is high, add moisture absorption devices or heating devices.
• Before re-commissioning, measure insulation resistance and conduct withstand voltage tests to confirm qualified insulation.

IV. Maintenance Notes

• Safety Specifications: Before maintenance, ensure power is cut off, electricity is tested, grounding wires are connected, and safety warning signs are set up; wear safety belts for high-altitude operations (such as inspecting the top of bushings).
• Record Keeping: Record oil level, temperature, test data, abnormalities, and handling measures in detail during each maintenance, and establish equipment records for traceability and trend analysis.
• Spare Parts Reserve: Reserve vulnerable parts in advance (such as gaskets, silica gel, fuses, tap changer contacts) to avoid delays in maintenance during faults.