Transformer oil treatment

1. Pressure filtration method

Using the pressure of the oil pump to make the oil pass through the filter paper with filtering function, the solid impurities are blocked, and the filter paper can also absorb a small part of the water, so that the oil can be purified. The pressure willing method has the advantages of simple equipment, convenient operation and maintenance, etc. Whether working alone or in combination with vacuum drying, the pressure oil filter works well.

Therefore, the pressure filtration method is widely used in the work.

(1) The structure of the pressure oil filter. There are various models of pressure oil filters, commonly used are domestic LY-50~150 type, mainly composed of oil inlet pipe, filter plate, filter paper, frame, crank handle, lead screw, motor, oil pump, mesh filter, pressure gauge and so on.

(2) The working diagram of the pressure oil filter is shown in Figure 1. In the figure, the incoming dirty oil passes through the filter screen 1 to remove impurities, and is sent to the oil filter 7 by the oil pump 2, and the clean oil passing through the oil filter paper is discharged through the valve 8. Pressure gauge 4 is used to test the internal working pressure of the pressure oil filter.

Transformer oil treatment
Figure 1 – Working diagram of the pressure oil filter

1- filter screen; 2- oil pump 1; 3, 5, 8- valve; 4- pressure gauge; 6- oil tank; 7- oil filter

(3) Oil filtering process. The flow of oil in the oil filter is shown in Figure 2. The oil filter paper is sandwiched between the filter plate and the filter frame. There are oil flow holes on the bottom two corners of the filter plate and the filter frame, and the dirty oil fills the entire filter frame through the oil inlet holes on the filter frame. Under the action of pressure, the oil passes through the oil filter paper and flows out from the oil outlet holes on the filter plate. The combination of filter plate and filter frame can be as many as 20 to 30, so the filtering effect is better. In order to enhance the penetration ability of the oil, the viscosity of the oil must be reduced, so the oil entering the pressure oil filter should be kept at a temperature of 50~60 °C, so as to improve the efficiency of the oil treatment.

Transformer oil treatment
Figure 2 – Oil flow in the filter press

1- filter plate; 2- filter back; 3- filter paper

Precautions for using pressure oil filter. It mainly includes the following aspects.

1) The oil filter paper used should be clean and dry. Generally, 2-3 pieces of filter paper are placed in a set of filter frames of the pressure oil filter, and the rough surface of the oil filter paper should face the direction of oil intake. The dirtier the oil, the more oil filter paper should be put, but too much oil will increase the resistance of oil passing through.

2) For oil with better quality, the paper can be changed once every 2 hours, and the paper should be changed frequently for dirty oil.

3) Before using the oil filter, check the power supply, whether the oil filter and the filter screen are clean, whether there is dried filter oil in the pole plate, whether the rotation direction is correct, whether the casing is grounded, and whether the pressure gauge indication is correct.

4) When starting the oil filter, the oil outlet valve should be opened first, then the oil inlet valve should be opened, and the operation sequence is reversed when it stops; when a heater is installed, the oil filter should be started first, and the heater should be put into operation after the oil flow has passed. The operation sequence is reversed when it stops. The pressure of the oil filter is generally 0.25-0.4MPa, and the maximum does not exceed 0.5MPa.

2. Vacuum oil filter method

Vacuum oil filtration method, also known as vacuum spray oil filtration method, is one of the better methods to remove moisture in oil. After the oil is heated, the temperature of the water in the oil also increases, and the vacuum degree in the mist tank is very high. When the oil and water are sprayed at the same time, both the oil and the water form mist-like particles. Because the particles themselves have a certain amount of heat, the saturated vapor pressure of oil is low and the saturated vapor pressure of water is high, and the water particles quickly form a vaporized state and are sucked away by the vacuum pump. Oil has a high heat capacity, so its particles can still be re-synthesized into oil particles and drop into the tank.

When working, use the pressure oil filter to filter out the solid debris and dirt in the oil, and send the hot oil to the vacuum atomization tank through the heater for atomization and evaporation of water. The vacuum atomizing tank is often maintained at the requirement of vacuum degree (95kPa), and the water vapor is quickly pumped and discharged by the vacuum pump (2X-30 type). The system can handle the oil used in transformers of 35kV and above well.

It can also be heated by winding the eddy current diagram of the tank wall of the oil storage tank, but the temperature of the tank wall generally does not exceed 95 ℃ during the treatment process, and the oil temperature does not exceed 85 ℃.

The oil pump can choose a gear oil pump with a flow rate of 100~1501/min and a pressure of 0.5MPa, or can be replaced by a pressure oil filter.

The vacuum degree of the vacuum tank can be determined according to the situation of the tank, and the general residual pressure is 0.21MPa.