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What is the difference between dry-type transformer and oil-immersed power transformer? How to choose between the two?

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What is the difference between dry-type transformer and oil-immersed power transformer? How to choose between the two?

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What is the difference between dry-type transformer and oil-immersed power transformer? How to choose between the two?

1. About dry-type transformer
Dry-type transformer refers to the transformer whose iron core and winding are not immersed in insulating oil. Dry-type transformer cooling methods areNatural Air Cooling (AN)withForced air cooling (PF)Two kinds. Dry-type transformer structure types areFixed Insulation Enclosure (Type SCB)andUnwrapped winding structureTwo kinds. From the relative position of the high and low voltage windings, there are two kinds of concentric and overlapping. The concentric structure is simple and easy to manufacture, and most dry-type transformers use this structure.The overlapping type is mainly used in the manufacture of special transformers.

 

2. Dry-type transformer specification
toSCB-11-1250KVA/10KV/0.4KV dry type transformerFor example, to explain the meaning of dry-type transformer model: in the above model specification, s means three-phase power transformer, c means transformer winding is resin cast solid, g means winding external insulation medium is air, B means parking winding winding, r means winding winding winding, 11 is series number, 1250KVA is transformer rated capacity, 10KV is transformer primary side rated voltage, 0.4KV is the rated voltage of transformer secondary side.

 

3. Technical parameters of dry type transformer
Dry type transformer technical parameters are:
① Frequency 50Hz
② No-load electric power, less than 4% required
③ Low voltage compressive strength: 2KV/min without breakdown
④ Insulation resistance at low voltage side shall not be less than 2MΩ
⑤ Winding connection mode:/Y/yn0, and D/yn0
The coil allowable temperature rise of 100K
⑦ Heat dissipation mode: natural air cooling or temperature control air cooling
Noise figure less than 30dB
 
The loss parameters of various capacity dry-type transformers (SCB type) are shown in Table 1.
 
4. Operating environment requirements for dry-type transformers
The environmental requirements for dry-type transformer operation are as follows:
① Ambient temperature -10-45 °
② Air relative humidity: daily average not more than 95%, monthly average not more than 90%
③ Altitude below 1600 m (at rated capacity)

 

5. Dry-type and oil-immersed transformer respective advantages and disadvantages

Dry-type transformers are more expensive than oil-immersed transformers in cost. The capacity of the oil-immersed transformer is larger than that of the dry-type transformer. Dry-type transformers shall be used in underground floors, floors and crowded places. Oil-immersed transformers are used in independent substation. Dry-type transformers are generally used in box-type substations. When the space is large, the oil-immersed transformer is used, and when the space is crowded, the transformer is used. When the regional climate conditions are humid, use oil-immersed transformers. Dry-type transformers shall be used in places requiring "fire and explosion protection. Dry-type transformers are less capable of withstanding loads than oil-immersed transformers. Dry-type transformers shall be operated at rated capacity. The oil-immersed transformer is allowed to be overloaded for a short time.

 

6. The difference between SCB type dry type transformer and SGB type transformer
In the winding coil:The low-voltage coil of SCB type dry-type transformer is wound with foil.Winding structure:The use of copper foil single-layer winding, interlayer materials containing latent curing agent of epoxy resin and lower composite foil.Winding material:Excellent conductivity of oxygen-free copper, copper content of 99.99%. The low-voltage coil of SGB dry-type transformer is wound with wire.Winding structure:Cylindrical coil, a plurality of ordinary glass wire coated flat copper wire.
 
SGB type dry-type transformer anti-short circuit ability is stronger than SCB type dry-type transformer.
 
In terms of heat dissipationSCB type dry-type transformer is better than SGB type transformer.
In terms of band load lossSCB type dry transformer is lower than SGB type dry transformer.
In terms of temperature rise,SCB type heat dissipation is better than SGB type.

 

7. Price Comparison of SGB, SCB and S13 Power Transformers
Taking the rated capacity of 1250KVA power transformer as an example, we can find the same type of manufacturer's quotation on the Internet for comparison.
SGB11---1250KVA/10KV/0.4KV, SCB11-1250KVA/10KV/0.4KV, S13-1250KVA/10KV/0.4KV power transformers, previously quoted by a factory were 93800 yuan/set, 95600 yuan/set 59600 yuan/set respectively. From this, we can see that the price difference between SCB and SGB is not big,Dry-type transformers are about 1.5 times the price of oil-immersed transformers.

 

8. Loss Parameters of S13 Oil-immersed Power Transformer
The loss parameters of S13 oil-immersed power transformer are shown in Table 2.

From Table 1 and Table 2,The no-load loss of dry-type transformer is larger than that of oil-immersed transformer. Dry-type transformer load loss is smaller than the oil-immersed transformer.

 

9. Guidelines for selection of power transformers
When selecting transformers, refer to GB/T17468---2008 "Guidelines for Selection of Power Transformers" and GB4208----2008 "Enclosure Protection Level (IP Code)" to select power transformers suitable for the environmental requirements of the site.
 
General principles for the selection of power transformers:In the selection of transformer technical parameters, should be based on the overall reliability of the transformer, comprehensive consideration of the technical parameters of the advanced and reasonable, economic, combined with the operation mode, the technical and economic indicators. At the same time, it is also necessary to consider the possible impact on the safe operation of the system, environmental protection, material saving, transportation and installation space.

 

10. Power transformer selection examples
SCB type dry-type transformers were originally designed for three transformers (1250KVA transformer 2 and 400KVA1) in a newly-built cold-rolled strip steel mill on an industrial platform. The owner unit supervisor to the author to consult the 3 transformer price. According to the plant site, environment and load conditions, the author suggests that the cold-rolled strip steel plant should choose oil-immersed sealed S13--M power transformer instead. This factory accepted the author's suggestion, which not only saved a lot of valuable funds, but also met the production requirements economically and with high performance. Oil-immersed power transformers have mature technology, natural air cooling, stable quality, strong short-circuit resistance, suitable for high humidity and high temperature environments, strong overload capacity, long life, and the price is about 2/3 of dry-type transformers.Therefore, unless there are fire requirements for dry-type transformers, oil-immersed sealed power transformers should be preferred.

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