Transformer Daily Maintenance Guide

Introduction

Transformers are critical in power systems, and their stable operation relies on daily maintenance to prevent faults like insulation aging or short circuits, which can cause outages and losses. This guide highlights maintenance significance-safety assurance, lifecycle cost reduction, and system stability. It details core tasks: appearance checks, insulating oil testing, electrical performance verification, cooling system upkeep, and relay protection checks. It also covers environmental strategies, special condition maintenance, and typical fault solutions.

Significance of Transformer Maintenance

A. Safety Assurance

Transformers are crucial components in the power system. Malfunctions can lead to severe consequences such as large – scale power outages, equipment damage, and even fire hazards. For example, in 2023, an unmaintained transformer in an industrial park experienced an internal short – circuit due to aging insulation, resulting in a fire that caused direct economic losses exceeding 2 million yuan. Regular maintenance helps detect potential safety hazards like insulation degradation and poor connections in advance, effectively preventing such accidents.

B. Economic Benefits

The replacement cost of transformers ranges from hundreds of thousands to tens of millions of yuan. In contrast, the investment in daily maintenance is only 1% – 3% of the equipment’s original value. By properly maintaining the transformer, its service life can be extended to over 25 years (compared to an average of 15 years for unmaintained ones), significantly reducing the overall life – cycle cost. Moreover, a well – maintained transformer can maintain an operating efficiency of over 98%, minimizing power losses. For a 1000kVA transformer, this can save more than 10,000 yuan in electricity costs annually.

C. System Stability Support

Transformer failures can trigger chain reactions in the power system, disrupting the operation of medical equipment, production lines, and other critical facilities. Daily maintenance ensures the stable operation of transformers under various conditions, such as load fluctuations and extreme weather, providing stability to the entire power system.

Detailed Content of Daily Maintenance Work

1. Appearance Inspection

Case and Structural Components

• Check the transformer tank for deformation, weld cracks, and rust. If the rusted area exceeds 10% of the surface area, immediate rust removal and painting are required.
• Verify that the torque values of flange connection bolts meet the specifications (for M16 bolts, the torque should be 40 – 50N·m) to prevent leakage due to seal failure.

Bushings and Insulators

• Use an infrared thermometer to measure the temperature rise of bushings. The temperature difference between phases should not exceed 2°C.
• Measure the surface contamination degree with a salt density meter. When the equivalent salt density is greater than 0.1mg/cm², live – line cleaning is necessary. Replace bushings immediately if cracks or damage are detected.

Tap Changers

• Manually operate the tap changer to switch through all gear positions. Record the operating torque for each gear (should be ≤ 30N·m). After switching, measure the DC resistance of each gear with a multimeter, and the three – phase unbalance rate should be ≤ 1%.
• Ensure that the rainproof cover of the operating mechanism is intact and add special silicone – based grease when the internal lubricating grease is insufficient.

Accessory Integrity

• Check the clarity of the oil – level gauge in the conservator. The oil level should be within the corresponding scale lines at ±20°C.
• Ensure the pressure relief valve’s lead seal is intact, and its manual test button should operate flexibly with no leakage after reset.

2. Insulating Oil Quality Testing

Regular Testing Items

• Check the oil level and color (normally light yellow and transparent) monthly. Test the breakdown voltage (≥ 35kV), moisture content (≤ 20ppm), and dielectric loss (≤ 0.005 at 90°C) quarterly.
• Conduct oil chromatographic analysis annually, with particular attention to acetylene (≤ 5μL/L), total hydrocarbons (≤ 150μL/L), and hydrogen (≤ 50μL/L) content. If the acetylene concentration suddenly increases, stop the transformer immediately for inspection.

Oil Quality Treatment Standards

• When the breakdown voltage is less than 30kV or the moisture content is greater than 30ppm, start vacuum oil filtration. After filtration, the particle size in the oil should reach NAS 7 level.
• When the acid value is greater than 0.1mgKOH/g, the oil needs to be replaced. Before replacement, flush the inner wall of the oil tank with hot oil circulation (oil temperature 80 – 90°C, circulation time ≥ 8 hours).

Maintenance of Breather

• Check the desiccant in the breather monthly for moisture absorption (the proportion of blue desiccant turning pink should be ≤ 1/3). Bake the moist desiccant in an oven at 120°C for 8 hours before reuse. When replacing the desiccant, close the breather valve first to prevent air from directly entering the oil tank.

3. Electrical Performance Testing

Insulation Resistance Test

• Measure the insulation resistance every six months using a 2500V megohmmeter. The insulation resistance between the high – voltage side and the low – voltage side and ground should be ≥ 1000MΩ, the absorption ratio (R60/R15) should be ≥ 1.3, and the polarization index (R10/R1) should be ≥ 2.0. Discharge fully for more than 10 minutes before testing.

DC Resistance Test

• Test the DC resistance of each phase winding annually. The deviation from the previous measurement value should be ≤ 2%, and the resistance deviation of each gear position of the tap changer should be ≤ 1%. Use the four – terminal method for measurement with a test current of ≥ 10A to eliminate the influence of contact resistance.

Dielectric Loss and Capacitance Test

• Measure the dielectric loss (≤ 0.5% at 20°C) and capacitance of the windings every two years. The capacitance value deviation should be ≤ 5%. If the dielectric loss suddenly increases by more than 50%, investigate insulation aging or moisture ingress.

Partial Discharge Detection

• For newly commissioned transformers, detect partial discharge every three months within the first year, and then annually. The partial discharge amount should be ≤ 10pc (at 1.73 times the rated voltage). Use an ultrasonic locator to accurately locate the discharge position.

4. Temperature Control and Cooling System Maintenance

Calibration of Temperature Control Devices

• Calibrate the oil – temperature gauge with a standard thermometer every six months, with an error of ≤ ±2°C. Set the action values of the temperature controller as follows: start the fan at 80°C, start the standby fan at 90°C, and trip at 105°C. Simulate and test to ensure reliable action.

Cooler Maintenance

• For forced – oil – circulation air – cooled systems (OFAF), check the balance of fan blades monthly (vibration velocity ≤ 6.3mm/s) and the bearing temperature rise of the motor ≤ 40K.
• Blow the heat sink fins of the cooler with compressed air quarterly. When severely dusty, rinse with clean water below 50°C to ensure that the heat dissipation efficiency does not decrease by more than 10%.

Oil Pumps and Pipelines

• The running sound of the oil pump should be uniform without abnormal noise, and the outlet pressure should be maintained at 0.05 – 0.1MPa.
• Check the switch status of pipeline valves annually. When the differential pressure of the filter is greater than 0.02MPa, clean the filter element to prevent oil passage blockage.

5. Relay Protection and Signal System Verification

Gas Protection

• Calibrate the light – gas action value to 250 – 300mL, and set the heavy – gas flow velocity to 1.0 – 1.2m/s (for oil – immersed transformers). Use a special calibration instrument to simulate the oil flow velocity to ensure accurate signals and reliable actions. Keep the inside of the relay clean and check for water accumulation and rust annually by opening the cover.

Differential Protection

• Conduct vector testing quarterly, and the differential current value should be ≤ 0.05In. During on – load testing, the current phase and amplitude on each side should meet the setting requirements, and the differential current unbalance rate should be ≤ 5%.

Signal Loop Check

• Simulate fault signals such as high oil temperature, low oil level, and pressure relief to ensure clear audible and visual alarms and no delay (≤ 1 second) in remote transmission to the monitoring system. The grounding resistance of the signal cable shield layer should be ≤ 1Ω to prevent interference and misoperation.

Environmental Adaptability Maintenance Strategies

Maintenance Points for Special Working Conditions