Transformer deoiling process requirements

Transformer deoiling process requirements

Transformer deoiling (such as draining, flushing, and vacuum deoiling) is a key step in destruction, oil change, or fault handling. It is necessary to strictly follow the process standards to ensure equipment safety and oil quality stability. The following are specific process requirements:

1. Preparation before deoiling

(I) Safety measures

- Power outage and power failure: Confirm that the transformer is powered off and the high and low voltage sides are grounded.

- Gas protection signal change: Prevent the gas relay from tripping when draining oil.

- Preparation: Fire extinguishers (such as dry powder, CO2) are equipped on site, and open flames are prohibited for firefighting.

(II) Environmental conditions

- Humidity control: Relative humidity ≤ 60%, avoid working in rainy days or in high humidity environments.

- Oil temperature control: The oil temperature should be between 20 and 50 °C (low temperature oil has high viscosity, which affects the oil discharge speed).

(3) Equipment inspection

- Oil pipeline sealing: Check valves, flanges, and oil pumps for leakage.

- Cleanliness of oil storage tank: Spare oil tanks must be dry and undamaged (to prevent contamination of old oil).

2. De-oiling process requirements

(1) Oil drainage method

- Gravity oil drainage: natural discharge through the oil drain valve at the bottom of the transformer (applicable to small-capacity transformers).

- Oil pumping: Use a vacuum oil filter or gear pump to accelerate oil drainage (commonly used for large-capacity transformers).

- Vacuum de-oiling: Use a vacuum pump to vacuum the transformer and completely remove residual oil (applicable to blockage or oil change).

(2) Oil drainage speed control

- Frequent oil drainage: ≤100 L/min (to avoid oil flow electrification or oil tank deformation).

- Vacuum de-oiling: vacuum extraction rate ≤10 kPa/min (to prevent insulation parts from being subjected to mechanical stress).

(3) Residual oil treatment

- Residual oil at the bottom of the oil tank: Use an oil suction machine or a lint-free cloth to clean it to ensure that there is no residue.

- Dead corners, such as brackets and supports, need to be drained or flushed separately.

3. Key quality control points

(1) Oil quality inspection (before and after oil drainage)

| Inspection items | Standard requirements | Inspection methods |

|--------------------|------------------------------------------|--------------------|

| Breakdown voltage | ≥40 kV (operating oil) | GB/T 507|

| Moisture content | ≤20 mg/L (operating oil) | GB/T 7600|

| Acid value | ≤0.1 mg KOH/g | GB/T 264|

| Gas content | ≤1% (volume ratio) | DL/T 423 |

(2) Vacuum deoiling process (if required)

- Vacuum requirements:

- 110 kV and below: residual pressure ≤133 Pa

- 220 kV and above: residual pressure ≤50 Pa

- Pumping time:

- 110 kV: ≥4 hours

- 220 kV: ≥8 hours

- 500kV: ≥24 hours

(3) Secondary pollution prevention

- Oil pipe sealing rubber: Use stainless steel or oil-resistant pipes to avoid plastic pipe failure.

- Oil tank identification: Old oil and new oil are stored in separate tanks, and the oil quality status is marked (such as "to be filtered" and "scrap").

4. Post-deoiling treatment

(1) Transformer internal inspection

- Iron core and bracket: Check for moisture and drainage marks (use hot air drying if necessary).

- Oil tank cleaning: Rinse with anhydrous ethanol or transformer oil to remove sludge and metal particles.

(2) Oil filling or sealing

- Immediate oil filling: If re-oiling is required after the pollutants are absorbed, it should be completed within 24 hours to prevent moisture from the insulating parts.

- Long-term sealing: If the transformer needs to be idle, it should be filled with dry low-pressure (pressure 0.01~0.03 MPa) to prevent moisture.

5. Safety precautions

1. Explosion-proof requirements:

- Do not knock on the oil tank or use tools that are prone to sparks when draining oil.

2. Environmental protection requirements:

- Waste oil is recycled according to GB 14554 standards and direct discharge is prohibited.

3. Personal protection:

- Operators wear oil-proof gloves and goggles to avoid contact with high-temperature oil.

6. Common problems and countermeasures

| Problems | Causes | Solutions |

|---------------------|------------------------|----------------------------------|

| Slow oil drainage | Oil temperature is too low or valve is blocked | Heat oil to 40~50℃, clean valve |

| Vacuum degree does not meet the standard | Poor sealing or vacuum pump failure | Check flange gasket and ｒｅｐｌａｃｅ vacuum pump oil |

| High gas content in oil | Insufficient vacuum pumping time | Extend vacuum pumping time to standard requirements |

The core of the transformer deoiling process is safety, thoroughness and pollution-free, and the following should be focused on:

1. Control of oil drainage speed and vacuum degree to avoid equipment damage.

2. Oil quality detection to ensure that subsequent treatment (such as filtration and oil change) has a basis.

3. Environmental protection and safety, standardize the treatment of waste oil, and eliminate fire and pollution risks.

Strictly following the standard operation can extend the life of the transformer and ensure the stable operation of the power grid.