Dry type transformer and oil immersed transformer difference

1. About dry transformers

Dry type transformer refers to the transformer whose iron core and windings are not impregnated with insulating oil. Dry type transformer cooling methods include natural air cooling (AN) and forced air cooling (PF). There are two types of dry type transformer construction: fixed insulation wrap (SCB type) and unwrapped winding structure. From the relative position of high and low voltage winding, there are two concentric and overlapping types. Concentric type is simple in structure and convenient in manufacture. Most dry type transformers adopt this structure. Overlapping type is mainly used in the manufacture of special transformers.

2. Dry type transformer specifications

Take SCB-11-1250kva /10KV/0.4KV dry type transformer as an example to explain the significance of dry type transformer model: In the above model specifications, S stands for three-phase power transformer, C stands for resin cast solid transformer winding, G in the position of letter C stands for air insulating medium outside the winding, B is the moored winding, R in the position of B stands for winding winding, 11 is the series number, 1250KVA is the rated capacity of the transformer, 10KV is the rated voltage of the primary side of the transformer. 0.4KV is the rated voltage of the secondary side of the transformer.

3. Technical parameters of dry transformer

Dry type transformer technical parameters are:

① Frequency 50Hz

② No load current, the requirement is less than 4%

③ Low pressure strength: 2KV/min no breakdown

④ The low voltage side of insulation resistance shall not be less than 2MΩ

⑤ Winding connection mode: /Y/yn0 and D/yn0

⑥ Coil allows temperature rise of 100K

⑦ Heat dissipation mode: natural air cooling or temperature control air cooling

⑧ The noise factor is less than 30dB

The loss parameters of dry type transformers (SCB type) with various capacities are shown in Table 1.


4. Operating environment requirements of dry type transformer

Environmental requirements for dry type transformer operation are as follows:

① The ambient temperature is -10--45°

② Air relative humidity: the daily average is not more than 95%, the monthly average is not more than 90%

③ The height of the sea dial is below 1600 meters (under the rated capacity).

5. Advantages and disadvantages of dry type and oil immersed type transformer respectively


Dry transformer is more expensive than oil - immersed transformer in cost. Capacity The capacity of oil-immersed transformers is larger than that of dry transformers. Dry transformers should be used in underground floors, floors and crowded places. Oil-immersed transformers are used in independent substations. Box substations generally use dry transformers. When the space is large, use oil-immersed transformer, and when the space is crowded, use dry transformer. When the regional climate is humid, the oil immersed transformer is used. Dry transformers are used where "fire and explosion proof" is required. The capacity of dry transformer to bear load is worse than that of oil - immersed transformer. Dry type transformer shall operate at rated capacity. Oil - immersed transformers allow short - time overload.

6. SCB type dry type transformer and SGB type transformer difference

In winding coil: SCB type dry transformer low-voltage coil using foil winding. Winding structure: copper foil is wound in a single layer, and the interlayer material contains epoxy resin with latent curing agent and the lower composite foil. Winding material: The use of excellent conductivity of oxygen free copper, copper content 99.99%. The low voltage coil of SGB dry transformer is wound by wire. Winding structure: cylindrical coil, many ordinary glass - wrapped flat copper wire.

SGB type dry transformer is stronger than SCB type dry transformer.

In terms of heat dissipation, SCB type dry transformer is better than SGB type transformer.

SCB type dry transformer is lower than SGB type dry transformer in terms of load loss.

In terms of temperature rise, SCB type heat dissipation is better than SGB type.

7. Price comparison of SGB, SCB and S13 power transformers

Take the rated capacity of 1250KVA power transformer as an example, find the same type of manufacturers on the Internet quotation for comparison.


SGB11-- 1250KVA/10KV/0.4KV, SCB11 --1250KVA/10KV/0.4KV, S13 --1250KVA/10KV/0.4KV power transformers, before a factory quoted 93800 yuan/machine, 95600 yuan/machine 59600 yuan/machine. From this point on, the price difference between SCB type and SGB type is not big, dry transformer is about 1.5 times the price of oil-immersed transformer.

8. Loss parameters of S13 oil-immersed power transformer

The loss parameters of S13 oil-immersed power transformer are shown in Table 2.


It can be seen from Table 1 and Table 2 that the no-load loss of dry transformer is larger than that of oil-immersed transformer. Dry transformer load loss is smaller than oil - immersed transformer.

9. Power transformer selection guidelines

In the selection of transformer should refer to GB/T17468-- 2008 "power transformer selection guidelines" and GB4208----2008 "shell protection level (IP code)", choose suitable for the site environmental requirements of the power transformer.

General principles of selection of power transformer: when choosing transformer technical parameters, should be based on the overall reliability of the transformer, comprehensive consideration of the advanced and rational technical parameters, economy, combined with the operation mode, put forward technical and economic indicators. At the same time, we should consider the possible impact on the safe operation of the system, environmental protection, material saving, transportation and installation space.

10. Examples of power transformer selection

SCB type dry type transformer used in three transformers (1250KVA transformers 2, 400KVA1 transformers) designed for a new cold strip rolling mill on an industrial platform. Owner unit supervisor to the author to consult the price of these 3 transformers. According to the site, environment and load of this plant, the author suggests that the oil immersed sealed S13- M power transformer should be selected for cold strip mill. This factory accepted the author's suggestion, which not only saved a lot of precious funds, but also met the production requirements economically and with high performance. Oil-immersed power transformer technology is mature, natural air cooling, stable quality, strong short-circuit resistance, suitable for high humidity and high temperature environment, strong overload capacity, long life, the price is about two-thirds of dry transformer. Therefore, unless there are fire requirements to choose dry transformer requirements, otherwise, oil-immersed sealed power transformer should be preferred.