Dry type transformer vs oil type transformer

The construction of transformers in power engineering construction can be described as a very important part. Among them, what we often hear are dry-type transformers (referred to as dry transformers) and oil-immersed transformers (referred to as oil transformers). What are the main differences between transformers and oil-immersed transformers, and what are the advantages and disadvantages of each?

The biggest difference between oil-immersed transformers and dry-type transformers is whether there is "oil". Since oil is liquid and has fluidity, oil-immersed transformers must have a shell. The inside of the shell is transformer oil, and the transformer is immersed in the oil. The coil of the transformer cannot be seen from the outside; while the dry-type transformer has no oil, the outer shell is not needed, and the coil of the transformer can be directly seen; there is also an oil pillow on the oil-immersed transformer, which is stored inside It uses transformer oil, but now there are new oil-immersed transformers without oil pillows.

They are all power transformers, and they all have iron cores for magnetic circuits and windings for circuits. The biggest difference is between the "oil type" and the "dry type". That is to say, the cooling medium of the two is different. The former uses transformer oil (of course, other oils such as β oil) as the cooling and insulating medium, and the latter uses air or other gases such as SF6 as the cooling medium. The oil change is to put the body composed of iron core and winding in an oil tank full of transformer oil. Dry change often encapsulates the iron core and windings with epoxy resin; there is also a non-encapsulated type that is used more now. The windings are impregnated with special insulating paper and special insulating paint to prevent windings or iron The core is damp.

Oil-immersed transformers are designed with a radiator outside for the convenience of heat dissipation, that is, to facilitate the flow of internal insulating oil, like a heat sink, while dry-type transformers do not have this radiator, and heat dissipation depends on the fan under the transformer coil.

Oil-immersed transformers are generally installed indoors or outdoors in separate transformers due to the need for fire protection, while dry-type transformers must be installed indoors, generally in the distribution room.

In terms of output and consumption, the current dry transformer voltage level is only 35kV, and the capacity is smaller than oil transformers, about 2500kVA. And because the dry transformer manufacturing process is more complicated than the oil transformer of the same voltage level and capacity, the cost is also high. Therefore, the amount of oil is still increasing. However, due to its environmental protection, flame-retardant and impact resistance, it is often used in high-demand power supply and distribution places such as hotels, office buildings, and high-rise buildings.

It can be seen that dry transformation and oil transformation have their own advantages and disadvantages. Oil transformation has low cost and easy maintenance, but it is combustible and explosive. Because of its good fire resistance, dry transformers can be installed in the center of the load to reduce voltage loss and power loss. However, the dry change is expensive, large in size, poor in moisture and dust resistance, and loud in noise.

In summary, we can see the following differences:

1. Appearance

Different packaging forms, dry-type transformers can directly see the core and coil, while oil-immersed transformers can only see the outer shell of the transformer;

2. Different lead forms

Dry-type transformers mostly use silicone rubber bushings, while oil-immersed transformers mostly use porcelain bushings;

3. Different capacity and voltage

Dry-type transformers are generally suitable for power distribution. Most of the capacity is below 2000kVA, the voltage is 10kV and below, and some have 35kV voltage levels; while oil-immersed transformers can achieve the required full capacity and voltage levels. All voltages are reached; the UHV 1000kV line under construction in China must be an oil-immersed transformer.

4. Insulation and heat dissipation are different

Dry-type transformers are generally insulated by resin, cooled by natural air, and large-capacity is cooled by fans; while oil-immersed transformers are insulated by insulating oil, and the heat generated by the coil is transferred to the radiator (sheet) of the transformer by the circulation of insulating oil inside the transformer. ) For heat dissipation.

5. Applicable places

Dry-type transformers are mostly used in places where "fire and explosion-proof" are required. Generally, large buildings and high-rise buildings should be used. Oil-immersed transformers may be sprayed or leaked after an accident, causing fires, and they are mostly used outdoors. And there are places for digging and setting up "accident oil ponds".

6. Different load bearing capacity

Generally, dry-type transformers should be operated under rated capacity, while oil-immersed transformers have better overload capacity.

7, the cost is different

For transformers of the same capacity, the purchase price of dry-type transformers is much higher than that of oil-immersed transformers.