Difference Between Dry-type Transformer and Oil-immersed Transformer

Advantages and disadvantages of dry-type transformer and oil-immersed transformer

Dry-type transformers are more expensive than oil-immersed transformers.
In terms of capacity, there are more oil-immersed transformers with large capacity than dry-type transformers.
Dry-type transformers are required in complex buildings (basements, floors, roofs, etc.) and crowded places. Oil-immersed transformers are used in independent substation sites.
Oil-immersed transformer can be selected when the space is wider, and dry transformer can be selected when the space is more crowded.
Oil-immersed transformers are easy to use in humid and hot regions. If a dry-type transformer is used, it must be equipped with forced air-cooling equipment.
Difference between dry-type transformer and oil-immersed transformer
1. Appearance
Different encapsulation forms, dry transformer can directly see the core and coil, while oil transformer can only see the 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 transformer is generally suitable for distribution, its capacity is mostly below 1600 KVA, voltage is below 10 KV, and some can achieve 35 KV voltage level; while oil-type transformer can achieve all capacity and voltage level from small to large; UHV 1000KV test line under construction in our country, oil-type transformer is used.
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. The biggest difference is between “oil” and “dry”. That is to say, the cooling medium of the two is different. 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 immersed transformer is to place the body consisting of iron core and winding in an oil tank filled with transformer oil.Dry-type transformer 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.)
As far as output and consumption are concerned, the 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 converter 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-change price is high, the volume is large, the moisture-proof and dust-proof property is poor, and the noise is big.
Oil immersed transformer gradually withdraws, dry type transfoemer can be disassembled transport easy, clean, easy to maintain, according to the installation does not need a seat, there is no oil seepage pool and so on.
It is better to distinguish from each other in appearance.
The greatest difference between oil-immersed transformer and dry-type transformer is whether there is “oil”. Because oil is liquid and has fluidity, oil-immersed transformer must have a shell. The inside of the shell is transformer oil, and the coils of transformer are immersed in oil, so the coils of transformer can not be seen from the outside. Without oil, dry-type transformer can see the change directly without shell. The coil of the transformer; another characteristic is that oil-immersed transformer has oil pillow on it and transformer oil is stored inside, but the new oil-immersed transformer also has transformer production without oil pillow.
Oil-immersed transformer for heat dissipation convenience, that is, for internal insulation oil flow and heat dissipation convenience, the external design of radiators, like heat sinks, while dry transformer does not have this radiator, heat dissipation depends on the fan under the transformer coil, the fan is a little like household air-conditioning indoor machine;
Oil-immersed transformers are usually installed indoors or outdoors as a result of fire protection. Dry transformers must be installed indoors. Generally, they are installed in low-voltage distribution rooms and side by side with low-voltage distribution cabinets.

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