The main differences and advantages and disadvantages of dry-type transformers and oil-immersed transformers

The construction of transformers in power engineering construction can be described as a very important part. Among them, we often hear dry-type transformers (referred to as dry-type transformers) and oil-immersed transformers (referred to as oil-type 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 soaked in the oil. The coil of the transformer cannot be seen from the outside; while the dry-type transformer has no oil, it does not need the outer casing, and the coil of the transformer can be seen directly; another feature is that the oil-immersed transformer has an oil pillow on it, which is stored inside. Transformer oil is used, but now new oil-immersed transformers are also available without oil pillows.

All power transformers have iron cores for magnetic circuits and windings for circuits. The biggest difference is in "oil type" and "dry type". That is to say, the cooling medium of the two is different. The former uses transformer oil (of course there are other oils such as beta 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 place the body composed of the iron core and the winding in an oil tank full of transformer oil. Drying often encapsulates the iron core and winding with epoxy resin; there is also a non-encapsulated type that is used more now, and the winding is impregnated with special insulating paper and then special insulating paint, etc., to prevent winding or iron. The core is damp.

For the convenience of heat dissipation, that is, the flow of internal insulating oil in the oil-immersed transformer, a radiator is designed on the outside, just like a heat sink, while the dry-type transformer does not have this radiator, and the 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, usually 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 that of oil transformers, about 2500kVA. In addition, because the dry transformer manufacturing process is more complicated than the oil transformer with the same voltage level and the same capacity, the cost is also high. Therefore, the amount of oil is still increasing. However, due to the advantages of dry change environmental protection, flame retardant, impact resistance, etc., it is often used in indoor and other high-demand power supply and distribution places, such as hotels, office buildings, high-rise buildings, etc.

It can be seen that dry transformer and oil transformer have their own advantages and disadvantages. Oil transformer has low cost and convenient maintenance, but it is flammable and explosive. Due to its good fire resistance, the dry transformer can be installed in the central area of ​​the load to reduce voltage loss and power loss. However, dry change is expensive, bulky, has poor moisture and dust resistance, and is noisy.

Next, let us summarize the differences mentioned above into the following seven points:

1. Appearance

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

2. Different lead forms

Most dry-type transformers use silicone rubber bushings, while most oil-immersed transformers use porcelain bushings;

3. Different capacity and voltage

Dry-type transformers are generally suitable for power distribution, the capacity is mostly below 2000kVA, the voltage is 10kV and below, and some have a voltage level of 35kV; while oil-immersed transformers can achieve all the required capacity and voltage level. When it comes to all voltages; the UHV 1000kV lines under construction in my country must be oil-immersed transformers.

4. Insulation and heat dissipation are different

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

5. Applicable places

Dry-type transformers are mostly used in places that require "fireproof and explosion-proof", and are generally suitable for large buildings and high-rise buildings; while oil-immersed transformers may have oil ejection or leakage after an "accident", causing fire, and most of them are used outdoors. And there are places where "accident oil pools" are dug.

6. Different load bearing capacity

Generally, dry-type transformers should operate at 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.