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Differences between Dry Type Transformer & Oil Filled Transformer

March 29, 2019

What is the Differences between Dry Type Transformer & Oil Filled Transformer? Here is the answer.

transformer types

transformer types


Different encapsulation forms, dry transformer can directly see the core and coil, while oil transformer can only see the transformer shell;

2.Different Lead Forms

Silicone rubber bushing is mostly used in dry-type transformer, while porcelain bushing is mostly used in oil-type transformer.

3.Different capacities and voltages

Dry-type transformers are generally suitable for distribution applications, with capacity mostly below 1600 KVA, voltage below 10 KV, and individual 35 KV voltage levels; while oil-type transformers can achieve all capacities from small to large, and voltage levels can also achieve all voltages; UHV 1000 KV test lines under construction in China must adopt oil-type transformers.

4.Insulation and heat dissipation are different

Dry-type transformers are generally insulated by resins, which are cooled by natural air and large capacity by fans. Oil-type transformers are insulated by insulating oil, which circulates in the transformer to heat the heat sink of the transformer.

5.Places of application

Dry-type transformers are mostly used in places requiring “fire prevention and explosion protection”, which are easy to be used in large buildings and high-rise buildings. Oil-type transformers may emit or leak oil after an accident, causing fires. Most of them are used outdoors, and there are places where “accident oil pools” are excavated.

6.Different Bearing Capacity to Load

Generally, dry-type transformer should operate under rated capacity, while oil-type transformer has better overload capacity.

7.The cost is different

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

Dry-type transformers generally start with SC (epoxy resin casting encapsulation), SCR (non-epoxy resin casting solid insulation encapsulation), SG (open type)

“Of course, the same thing is that all power transformers have iron cores for magnetic circuits and windings for circuits.

8. The cooling medium are is different

The biggest Differences between Dry Type Transformer & Oil Filled Transformer is “oil” and “dry”.

The former uses transformer oil (and other oils such as beta oil) as cooling and insulation medium, while the latter uses air or other gases such as SF6 as cooling medium. Oil type is to place the body consisting of iron core and winding in an oil tank filled with transformer oil.

Dry type often encapsulates iron core and winding with epoxy resin casting. There is also a kind of non-encapsulated type which is used more nowadays. The winding is impregnated with special insulating paper and special insulating paint to prevent dampness of winding or iron core. (And because the classification methods of technology, usage and structure are different, they derive different categories, so we think in a narrow sense.)

9. Production quantity and Consumption

At current, dry transformer voltage level is only 35 kV, and its capacity is smaller than that of oil transformer, which is about 2500 kVA. Moreover, the manufacturing process of dry transformer is more complex and costly than that of oil transformer with the same voltage level and capacity. So at present, the amount of oil is increasing.

However, due to the advantages of environmental protection, 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’re just a transformer user, it’s enough to know about this.

Each has its own advantages and disadvantages. Oil transformer has low cost and convenient maintenance, but it is flammable and explosive. Dry transformer can be installed in the load center area to reduce voltage loss and power loss due to its good fire resistance. But the dry-type price is high, the volume is large, the moisture-proof and dust-proof property is poor, and the noise is big. Oil type gradually withdraws, with dry change, dry change can be disassembled, transport easy, clean, easy to maintain, according to the installation without seat, no oil seepage pool and other advantages.

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