As the reliability requirements of power systems continue to rise, oil-immersed transformers have become indispensable key equipment in distribution networks. Their daily maintenance and service life management are increasingly critical concerns for plant electricians and O&M managers. With systematic and scientific maintenance, an oil-immersed transformer can operate reliably for more than 30 years. In contrast, poorly maintained equipment often experiences a sharp rise in failure rates after just 15 years and may even be scrapped prematurely. Xinhong Electrical, as a professional transformer manufacturer, has accumulated extensive practical experience in oil-immersed transformer maintenance over the years. This article systematically outlines the core points of oil-immersed transformer maintenance to help safeguard your equipment.
Insulating oil in an oil-immersed transformer serves the dual functions of insulation and cooling – it is the lifeblood of stable operation. Deterioration of insulating oil is the leading cause of transformer failures, with data showing that about 45% of transformer faults originate from insulation system failure.
Oil quality testing should follow a clear schedule and standards: Every 3–6 months, samples should be tested for breakdown voltage (≥35kV required), dielectric dissipation factor (≤0.5% at 90°C), water content (≤10 ppm), and acid value (≤0.1 mg KOH/g). When breakdown voltage falls below 35kV, it indicates that moisture, free carbon, oxides and other impurities have entered the oil, significantly reducing insulation strength. Timely oil filtration or replacement is required.
Oil level and temperature monitoring is a basic daily operation: Daily inspections should check whether the oil level in the conservator is within the marked range, ensuring the level fluctuates naturally with temperature changes. Generally, the top oil temperature of an oil-immersed transformer should not exceed 85°C, and the winding temperature should not exceed 95°C. Long-term over-temperature operation will accelerate oil aging and greatly shorten equipment life.
Breather maintenance directly affects moisture prevention: Inspect the silica gel desiccant in the breather weekly. If more than two‑thirds of the blue silica gel has turned pink, replace it immediately to prevent humid air from entering the tank and degrading the oil quality.
Transformers generate a large amount of heat during operation. The cooling capacity directly determines whether the equipment can continue working within a safe temperature range. Clogging or reduced efficiency of the cooling system will directly lead to abnormal oil temperature rise.
Radiator cleaning should be part of quarterly maintenance: Dust and oil deposits easily accumulate on radiator fins and should be thoroughly cleaned every quarter. An infrared thermometer can measure the temperature difference between the radiator inlet and outlet. If the difference is significantly reduced, it may indicate internal clogging – further cleaning is required.
Fan and oil pump operation must be checked regularly: Check that the fan motor insulation resistance is ≥1MΩ and ensure the cooling device starts/stops in coordination with the temperature control loop. Monthly inspection should verify that all cooling valves are fully open to prevent cooling failure caused by closed valves.
Periodic electrical preventive tests are the most effective way to detect potential hidden faults – they can nip problems in the bud before failures occur.
Insulation resistance testing should be performed annually: Use a 2500V megger to measure the insulation resistance of the high and low voltage windings to ground and between windings. The absorption ratio should be ≥1.3, and results should be compared with historical data. If the resistance value drops by more than 30%, further inspection for insulation aging or moisture ingress is required.
Dissolved Gas Analysis (DGA) is the most valuable diagnostic tool: Perform DGA every six months, focusing on characteristic gases such as hydrogen, methane, and acetylene. If the acetylene content reaches ≥5 μL/L or total hydrocarbons exceed the limit, it indicates possible internal partial overheating or discharge faults – immediate action is needed. Modern intelligent monitoring systems combined with DGA can detect potential faults up to six months in advance, extending transformer life by as much as 25%.
Other critical electrical tests cannot be overlooked: Annually perform DC winding resistance testing (phase deviation ≤2%), turns ratio testing, and dielectric dissipation factor testing to comprehensively assess winding condition and insulation system integrity. These maintenance activities are vital for the safe and reliable operation of oil-immersed transformers. As a professional transformer manufacturer, Xinhong Electrical strongly recommends users strictly follow these schedules.
Although each accessory on an oil-immersed transformer is relatively small, every one affects the overall reliability of the equipment.
Bushing inspection is key to preventing high‑voltage flashover: Bushing surfaces must be kept clean – wipe them every three months and check for cracks, discharge marks, or oil seepage. If cracks are found, replace the bushing immediately to prevent along‑surface flashover faults.
Terminals need periodic tightening: Copper terminals loosen over time due to thermal expansion and contraction. Loose contact increases contact resistance, causes local heating, and may eventually burn out the terminal. Tighten terminals every three months as needed.
Tap changer maintenance should follow operation count and service years: For on‑load tap changers, inspect contact wear every 5,000 operations or 5 years. For off‑load tap changers, measure DC resistance after each switching operation to ensure good contact, preventing winding overheating caused by poor tap contact.
Sealing and pressure relief devices must be calibrated regularly: Inspect flange sealing rings every 1–2 years – replace aging or hardened rings promptly to prevent oil leakage. Calibrate pressure relief valves, thermometers, oil level gauges and other protective devices annually to ensure they can release pressure in time if internal pressure rises abnormally, preventing tank rupture.
In addition to maintenance work on the equipment itself, proper operational management and environmental control have a profound impact on extending transformer service life.
Load management is central to equipment health: Never operate an oil-immersed transformer above its rated capacity for extended periods. It is recommended to keep the load factor below 80% and three‑phase current unbalance ≤5% to effectively slow the aging of the insulation system. When loads are well managed, oil-immersed transformers equipped with online oil degassing units can experience insulating oil life extended to 2–3 times that of conventional operation.
Installation environment directly affects service life: Choosing a well‑ventilated, dry location free of corrosive gases can significantly slow equipment aging. The transformer room should maintain humidity ≤85%, and rodent guards and fire‑fighting equipment must be installed with clear access.
Grounding system inspection should be carried out every six months: Measure grounding resistance – it should be ≤4Ω – and check the grounding conductor for corrosion or breakage. Ensure a reliable ground before the lightning season to prevent lightning overvoltage from breaking down the insulation.
Systematic maintenance records not only help track equipment performance trends but also provide reliable data for fault diagnosis. Each oil-immersed transformer should have its own maintenance file, recording daily oil temperature and level, each oil sample test result, electrical test data, and all repair work. With comprehensive equipment records, users can systematically track changes in equipment health, optimize future maintenance plans, and reduce unplanned downtime losses.
Maintaining an oil-immersed transformer is not a one‑off task but a systematic project that spans the entire equipment life cycle. From daily inspections to annual preventive tests, from oil quality monitoring to cooling system cleaning – strict control at every step lays a solid foundation for long‑term safe and stable operation. Through systematic and standardized maintenance management, equipment failure rates can be effectively reduced and the service life of an oil-immersed transformer extended to more than 30 years.
As a one‑stop equipment supplier and solution provider in the professional transformer manufacturing field, Xinhong Electrical is committed to delivering stable‑performance oil-immersed transformers and comprehensive maintenance technical support to customers worldwide. From initial product selection to life‑cycle maintenance guidance, Xinhong Electricalstands ready to protect your power system with professionalism and dedication. For any questions regarding oil-immersed transformer maintenance or product inquiries, please feel free to contact us
Jiangsu Xinhong Electrical Equipment Co., Ltd.
Professional Oil-Immersed Transformer Manufacturer
