Transformer Vacuum Oil Filling Operation Guide

As the main electrical equipment of power plants and substations, the insulation strength of transformers directly affects the safe and stable operation of transformers. Generally, there are two ways to inject oil after the transformer arrives at the site: direct oil injection and vacuum oil injection. Transformers with voltage levels of 110KV and above are normally used for vacuum filling.

Today, PureTech will share with you the transformer vacuum oil filling operation guide sand we hope it will be helpful to you!

Advantages of transformer oil filling under vacuum

1. It can greatly reduce the oil and water content of the transformer, thereby greatly enhancing the breakdown voltage of the transformer oil, that is, reducing the oil gap distance of the insulation of the body, resulting in a great reduction in the design cost of the transformer;

2. Due to vacuum oil filling, the gas content in the oil tank is very small, so the probability of the pressure release valve and the gas relay acting is reduced, which ensures the normal operation of the transformer in the power grid.

Operation steps of vacuum oil injection

1. Transformer vacuuming

After all accessories of the transformer are installed. Open all the valves of the accessories and components connected to the main body, and make all accessories (including coolers and radiators) connected to the main body except the oil conservator and gas relay to vacuumize the main body. If the oil conservator is designed according to the full vacuum, the oil conservator and the gas relay are also evacuated together.

After adding a vacuum valve and a vacuum gauge to the oil inlet valve on the top of the fuel tank, connect the vacuum pipeline, so that before evacuating the tank, close the vacuum valve and pump the vacuum of the pipeline alone, so as to find out the actual vacuum degree that the vacuum system itself can achieve. . The vacuum degree required by the entire vacuum system (including vacuum pumps, pipes, valves and vacuum measuring instruments, etc.) should be less than 10Pa. If it is greater than 10Pa, the vacuum treatment system should be checked or repaired.

Note down the start time of evacuation, the time to check the degree of vacuum during evacuation, the corresponding pressure and the time to reach 133Pa. When it reaches 133pa, stop vacuuming, check the vacuum measuring instrument every 10 minutes and record the value P1, and check the reading of the vacuum measuring instrument and record the data P2 every 30 minutes. Through the formula leak rate η=﹤ (P2-P1)xV﹥/T

η is the leak rate

V is the volume of transformer oil in liters

T is the direct time interval between P1 and P2, in seconds

The leakage rate should be less than 2000pa.L/S. If it is greater than this value, the leakage point of the transformer should be checked and the leakage should be repaired. If it is less than this leak rate, turn on the vacuum pump to continue vacuuming. This vacuum degree (133pa) is maintained under the condition that the vacuum pump continues to run. The vacuum is maintained for no less than 24 hours. It should be pointed out that if the vacuum pump is stopped to maintain the vacuum after the leakage test (static hold), it will not only affect the complete removal of water, but also in the event of leakage, it will cause the local insulation to get wet.

PureTech provides you Vacuum Pumping System for you to perform transformer evacuation before oil filling. Or you can use PureTech Double Stage Vacuum Transformer Oil Purifier to perform this function. Contact us for details.

2. Vacuum oil filling

Use a Double Stage vacuum transformer oil purifier to inject qualified transformer oil. The temperature of the injected oil is preferably 40 to 60 °C (the outlet temperature of the Transformer Oil Purifier), but it should not be lower than 10 °C and higher than 70 °C. The oil injection speed depends on the maintenance of the vacuum degree, which is generally (3-6) ton/h. If the vacuum degree drops, the oil injection speed should be appropriately reduced.

During oil filling, the vacuum pump continues to operate, and the valve to the tank remains the same as when evacuating, so that all components are evacuated together with the body. Oil filling should be done with a vacuum transformer oil purifier. During vacuum oil filling, oil should be fed from the oil filling valve at the lower part of the oil tank, so that the oil overflows from the outside of the coil to the inside of the coil, which can reduce the opening force of the oil on the coil enclosure. In order to prevent the oil from being pumped into the vacuum pump, when the oil is injected to the oil surface about 200-300mm away from the vacuum pump inlet, close the vacuum valve and stop vacuuming. However, the Vacuum Oil Purifier still does not stop pumping oil until the oil level is close to the place where the gas relay is installed, and then the Vacuum Oil Purifier is stopped. Then add oil higher than the position required by the oil level curve, and then bleed each accessory (casing, switch, gas relay, oil pillow, etc.), and finally discharge the oil to the standard position. For transformers with oil pillow vacuuming, the oil is directly injected to the standard position of the oil level.

Hot oil circulation: Open the butterfly valve between the oil tank and the oil conservator, extract the oil from the lower part of the oil tank, heat it to 65±5℃ by the vacuum oil purifier, and then return to the oil tank from the upper part of the oil tank. Circulate the oil inside the transformer tank at least twice.

PureTech Double Stage Vacuum Transformer Oil Purifier (for 110kv and above transformer) and Single Stage Vacuum Transformer Oil Purifier (for 66 kv and below transformer) can be in service for vacuum oil filling. They are equipped with oil pump, so it can perform the function of transformer oil filling under vacuum. Besides, they have electric heaters, which can perform hot oil circulation.

More information about transformer oil purifier or vacuum pumping system, please feel free to contact us !