The Difference between Dry Type Transformer and Oil Filled Transformer

Of course, the same is true that the power transformer will have a core for the magnetic circuit and a winding for the circuit. The biggest difference is in "oil filled" and "dry". That is to say, the cooling medium of the two is different. The former uses transformer oil (and of course 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. Oil filled transformer is to place the body consisting of iron core and winding in a fuel tank filled with transformer oil. Dry type transformer often encloses the core and windings with epoxy resin. There is also a kind of non-encapsulated type that is used nowadays. The windings are impregnated with special insulating paper with special insulating paper to prevent the windings or core from getting wet. (Because the two are derived from different categories due to different methods of process, use, and structure, we are narrowly speaking.)

In terms of production and usage, the current dry type transformer’s voltage rating is only 35kV. The capacity is small compared to oil filled transformer, about 2500kVA. Moreover, since the dry type transformer manufacturing process is complicated and costly with respect to the oil filled transformer of the same voltage level and the same capacity, the oil filled transformer is still much more in terms of the amount of oil. However, due to the environmental protection of dry change, flame retardant, impact resistance and so on, it is often used in indoor and other high-demand power supply and distribution sites, such as hotels, office buildings, high-rise buildings and so on. If you are just a transformer user, it should be enough to understand this.

Dry type transformers and oil filled transformers have their own advantages and disadvantages. Oil filled transformers are low in cost and easy to maintain, but they are flammable and explosive. Dry type transformers can be installed in the center of the load due to their good fire resistance to reduce voltage loss and power loss. However, dry type transformers are expensive, bulky, moisture-proof and dust-proof, and have high noise.

Oil filled transformers gradually withdrew from the market and dry type transformers were adopted. The dry type transformer can be disassembled, transported and drained, cleaned, easy to maintain, installed without a machine base, and without oil leakage pool.

The two are better distinguished from the outside.

The biggest difference between oil filled transformers and dry type transformers is whether there is "oil". Since the oil is liquid and has fluidity, the oil-immersed transformer must have a casing. Inside the casing is transformer oil, the oil is immersed in the coil of the transformer, and the coil of the transformer is not visible from the outside. The dry type transformer has no oil, so it does not need the outer casing, and the coil of the transformer can be directly seen. Another feature is that there is an oil pillow on the oil filled transformer, and the transformer oil is stored inside, but now the new oil filled transformer also has no oil pillow.

In order to facilitate heat dissipation, that is, for the convenience of the flow of internal insulating oil, a heat sink is designed outside the oil filled transformer, just like a heat sink. The dry type transformer does not have this radiator, and the heat is cooled by the fan below the transformer coil. The fan is a bit like an indoor unit for home air conditioning.

Due to the need for fire protection, oil filled transformers are typically installed indoors or outdoors in separate transformers. The dry type transformer is definitely installed indoors, and is usually installed in a low-voltage power distribution room and installed side by side with the low-voltage power distribution cabinet.

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