The Characteristics and Maintenance of Transformer Oil Immersed Types

Ⅰ. About transformer oil immersed types

During the long-term operation of the transformer oil immersed type, the cooling oil of the transformer begins to change color and deteriorate, forming sludge or oil seepage, the resistance increases, and the temperature of the transformer maintains a high level of operation, which will inevitably lead to increased consumption and electricity safety hazards. For example, on the basis of the normal loss of 10.8KW of a 1000KVA transformer, depending on the actual usage (overload, transformer oil deterioration), the loss may be doubled or higher (for specific data we can measure its DC resistance), and the monthly electricity bill of users increases implicitly. At present, quite a lot of users have almost never done maintenance and oil changes for transformer oil immersed types. Cumulatively, the owners not only pay a large amount of electricity bills without realizing it, but also do not meet the energy policy of sustainable development of low-carbon energy conservation and emission reduction. Maintenance and inspection can be carried out after power user terminal equipment is cut off, tested, grounded and hung with warning sign of "forbidden to close, someone is working".

Ⅱ. Characteristics of transformer oil immersed types

The low-voltage windings of transformer oil immersed types generally adopt the cylindrical structure of copper foil around the shaft, except the copper wire with small capacity. The high-voltage winding adopts a multi-layer cylindrical structure, so that the ampere-turn distribution of the winding is balanced, the magnetic leakage is small, the mechanical strength is high, and the short-circuit resistance is strong. The transformer oil immersed type is fully oil-filled and sealed. The corrugated oil tank shell adapts to the expansion of oil with its own elasticity, and is a permanently sealed oil tank. Transformer oil immersed types have been widely used in various power distribution equipment. The body (winding and iron core) of the transformer oil immersed type is installed in an oil tank filled with transformer oil, and the oil tank is welded with steel plates. The oil tank of medium and small transformers is composed of a box shell and a box cover. The body of the transformer is placed in the box shell, and the body of the transformer can be lifted out for maintenance when the box cover is opened.

Ⅲ. Electric power transformer oil immersed type testing

1. The variation range of the power supply voltage of the monitoring transformer should be within ±5% of the rated voltage to ensure the quality of the secondary voltage. If the power supply voltage is overhigh or overlow for a long time, the tap changer of the transformer oil immersed type should be adjusted to make the next voltage tend to be normal.

2. Whether the oil level, oil color and oil temperature of the transformer exceeds the allowable value, whether there is oil leakage, and whether the oil quality is qualified, otherwise replace it.

3. Check the oil temperature of the upper layer of the transformer, the temperature should not be higher than 85 ℃.

4. The high and low voltage insulation resistance should not be lower than 70% of the original factory value, and the DC resistance of the winding should not exceed 2% of the average value of the three-phase difference at the same temperature, nor should it be greater than 2% compared with the last measurement.