Power Knowledge | What Hazards Does Transformer Oil Deficiency Pose to Operation?

I. Core Functions of Transformer Oil: A Dual Protection Mechanism

1. Insulation Protection: Transformer oil has an insulation strength far higher than air, effectively isolating live components such as windings and cores to prevent partial discharge and insulation breakdown.
2. Heat Dissipation Medium: Oil-immersed transformers rely on oil circulation to carry away heat generated by winding and core losses. For large-capacity transformers, the heat dissipation efficiency of the oil directly impacts the equipment's service life.

II. Three Core Hazards of Oil Deficiency: Gradual Risk Escalation

1. Malfunction of Light Gas Protection and Early Warning Failure
   The gas relay (Buchholz relay) inside the transformer is a key device for monitoring oil level and internal faults. When the oil level drops below the relay’s open cup, air enters the relay chamber, triggering a "light gas protection" signal. If left unaddressed, this can lead to:

• Risk of False Signals: Prolonged oil deficiency exposes the relay to air, potentially causing misoperations due to changes in humidity and temperature, misleading maintenance personnel about real faults.
• Protection System Failure: In severe oil deficiency, if an internal short circuit occurs, gas generated by arc decomposition of insulating materials cannot be effectively monitored, possibly causing the "heavy gas protection" to fail to trip, delaying fault isolation and expanding the accident scope.

2. Sharp Drop in Heat Dissipation Efficiency and Equipment Overheating
   The heat dissipation capacity of transformer oil is directly related to its volume. When the oil level is too low:

• Reduced Winding Heat Dissipation Area: Part of the coil is exposed to air, whose thermal conductivity is only 1/50 that of transformer oil, causing a rapid rise in winding temperature. For a 1000kVA transformer, the winding temperature rise in an oil-deficient state may exceed the rated value by 30°C, accelerating insulation aging (every 8°C temperature increase halves the lifespan).
• Interrupted Oil Circulation: Forced oil circulation cooling systems (such as oil pumps and radiators) cannot operate normally due to insufficient oil volume. Even under no-load operation, heat from core eddy current losses cannot be effectively dissipated, forming a "thermal accumulation effect."

3. Insulation Failure and Breakdown Accidents
   When the oil level drops below the bottom of the windings, the core and windings are fully exposed to air, facing three insulation threats:

• Direct Air Erosion: Moisture and dust in the air adhere to the insulation paper and winding surfaces, reducing the creepage discharge voltage by approximately 40%. In environments with humidity >60%, the risk of partial discharge increases significantly.
• Turn-to-Turn Insulation Damage: Exposed conductors lose the insulating support of the oil, and may come into contact due to electromagnetic vibration, causing short circuits. Test data shows that the turn-to-turn insulation withstand voltage drops from 3kV under normal conditions to 1.2kV in an oil-deficient state.
• Chain Reaction of Arc Discharge: Once partial discharge occurs, arc energy rapidly decomposes air and insulating materials, generating flammable gases (such as hydrogen and methane). If the power is not cut off in time, it may lead to transformer tank explosion, threatening substation safety.

III. Common Causes of Oil Deficiency: Multi-dimensional Fault Origins

1. Seal Failure and Leakage:

• Aging of rubber seals (service life ~8-10 years), cracks in welded joints, or loose bolts on bushing flanges cause slow oil leakage. In areas with large temperature differences, thermal expansion and contraction exacerbate seal failure.

2. Maintenance Neglect and Misoperation:

• Failure to regularly check oil levels (recommended monthly), failure to vent air when refueling, or use of 不合格 oil (e.g., water content >30ppm) leads to undetected continuous oil level decline.

3. Environmental and Design Defects:

• Outdoor transformers exposed to ultraviolet light and acid rain may develop rust perforations due to damaged anti-corrosion coatings on the tank. Some old transformers have insufficient conservator volume to accommodate oil volume fluctuations caused by load changes.

IV. Graded Protection Strategies: Prevention and Emergency Handling

1. Daily Monitoring and Preventive Maintenance

• Oil Level Visual Management: Install magnetic flap oil level gauges or electronic oil level sensors, setting early warning thresholds (e.g., alarm triggered when oil level drops below 85% of normal).
• Regular Oil Quality Testing: Conduct oil chromatographic analysis every 1-2 years. If hydrogen (H₂) content exceeds 150ppm or total hydrocarbon content exceeds 100ppm, investigate for partial discharge caused by oil deficiency.
• Periodic Seal Replacement: Replace all seals during equipment overhauls (typically every 5-10 years), using oil-resistant and high-temperature-resistant fluororubber.

2. Abnormality Handling Procedures

• Response to Light Gas Alarm: Immediately shut down the equipment, check the oil level and the state of the breather silica gel (normal is blue, turns pink when damp). After confirming no leakage, refill with the same grade of insulating oil (subject to vacuum degassing treatment).
• Emergency for Severe Oil Deficiency: If the oil level is below 1/3 of the observation window, 严禁带电运行 (forbid live operation). Perform insulation resistance testing (high-voltage to low-voltage and ground ≥100MΩ) and withstand voltage testing (2.5x rated voltage for 1 minute). Only put into operation after confirming qualified insulation performance.

3. Technical Upgrades and Design Optimization

• Intelligent Oil Level Monitoring System: Integrate pressure sensors and temperature compensation algorithms to calculate the real oil level in real time (eliminating the impact of temperature on oil volume), with data synchronized to the operation and maintenance platform.
• Self-Sealing Structure Design: Adopt fully oil-filled sealed transformers (e.g., corrugated tanks, expandable radiators) to prevent oil-air contact, eliminating the root cause of oil deficiency risks.

V. Conclusion: From "Post-Fault Handling" to "Proactive Protection"