1. About dry type transformer

 

Dry type transformers refer to transformers which are not immersed in insulating oil and iron core. The dry type transformer has two kinds of cooling methods: natural air cooling (AN) and forced air cooling (PF). There are two types of dry-type transformers: fixed insulation encapsulation (SCB type) and non enclosed winding structure. From the relative position of the high and low voltage winding, there are two concentric and overlapping modes. Concentric structure is simple and easy to manufacture. Most dry transformers use this structure. The overlap type is mainly used for 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 the type of dry-type transformer: in the above model specifications, S means three-phase power transformer, C means that the transformer winding is Resin-Cast solid, in the position of C letter, G means that the outer insulation medium of the winding is air, B is a parked winding, and R is in the position of B. It represents winding type winding, 11 is series number, 1250KVA is rated capacity of transformer, 10KV is rated voltage of primary side of transformer, and 0.4KV is rated voltage of secondary side of transformer.

 

3. Technical parameters of dry type transformer

 

The technical parameters of dry-type transformer are as follows: (1) frequency 50 Hz, (2) no-load power, less than 4%, and (3) low-voltage withstand voltage strength: 2KV/min without breakdown, (4) insulation resistance, low-voltage side not less than 2M, (6) winding connection mode: / Y/yn0, with D/yn0, (1) coil temperature allowed to rise 100 K, (1) heat dissipation mode: natural air cooling or temperature controlled air cooling, and (1) noise. The coefficient is less than 30dB. The loss parameters of various capacity dry type transformers (SCB) are shown in Table 1.

 

4. Requirements for dry transformer operation environment

 

The environmental requirements of dry-type transformer operation are as follows: 1. ambient temperature - 10 - 45 degrees, 2. air relative humidity: the average daily is not more than 95%, the average monthly is not more than 90%, 3. offshore height of 1600 meters (under rated capacity).

 

5. Advantages and disadvantages of dry and oil immersed transformers

 

In terms of cost, dry type transformers are more expensive than oil immersed transformers. The capacity of oil immersed transformer is larger than that of dry type transformer. Dry-type transformers are needed in underground, storeys and densely populated areas. Oil immersed transformers are used in independent substations. 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. Oil immersed transformers are used when the regional climate is relatively humid. Dry explosion-proof transformers are needed for fire protection and explosion protection. The capacity of dry type transformer to bear load is worse than that of oil immersed transformer. Dry type transformers should be operated at rated capacity. The oil immersed transformer is allowed to overload for a short time.

 

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

 

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

 

The SGB type dry type transformer is better than the SCB type dry type transformer in resisting short circuit.

 

In terms of heat dissipation, SCB type dry type transformers are better SGB transformers. In terms of load loss, the SCB type dry transformer is lower than the SGB type dry type transformer. In terms of temperature rise, the SCB type heat dissipation is better than the dry SGB type.

 

7, price comparison of SGB, SCB and S13 power transformers

 

Taking the rated capacity 1250KVA power transformer as an example, we compare the quotations of the same type manufacturers on the Internet. SGB11 11-1250KVA/10KV/0.4KV, SCB11-1250KVA/10KV/0.4KV, S13-1250KVA/10KV/0.4KV power transformer, Zhejiang Wenzhou factory quoted 93800 yuan / set, 95600 yuan / set 59600 yuan / set. From this we can see that the price difference between SCB and SGB is not big, and the price of dry-type transformer is about 1.5 times that of oil-immersed transformer.

 

8, loss parameter of S13 oil immersed power transformer

 

The loss parameter of S13 type oil immersed power transformer is shown in Table 2.

 

It is learned from table 1 and table 2 that the no-load loss of dry type transformers is larger than that of oil immersed transformers. The load loss of dry type transformer is smaller than that of oil immersed transformer.

 

9. Guide for selection of power transformers

 

The selection of transformer should refer to GB / T17468 - 2008 "Power Transformer Selection Guidelines" and GB4208 - 2008 "Shell Protection Grade (IP Code)" to select the power transformer suitable for the site environment requirements.

 

The general principle of selecting power transformer is that when selecting technical parameters of transformer, the technical and economic indexes should be put forward on the basis of the overall reliability of transformer, considering comprehensively the advancement, rationality and economy of technical parameters and combining with operation mode. At the same time, the possible impact on the safe operation of the system, environmental protection, material saving, transportation and installation space should also be considered.

 

10. Examples of power transformer selection

 

Three SCB dry-type transformers (2 1250KVA transformers and 400 KVA1 transformers) were originally designed for a new cold-rolled strip mill on an industrial platform. The owner of the unit advised the author about the price of the 3 transformers. According to the site, environment and load conditions of the plant, the author suggests that the cold-rolled strip mill should change to oil-immersed sealed S13-M power transformer. The factory accepted the author's suggestion, which not only saved a lot of valuable funds, but also met the production requirements economically and efficiently. Oil-immersed power transformer has mature technology, natural air cooling, stable quality, strong short-circuit resistance, suitable for high humidity and high temperature environment, strong overload capacity, long life and price is about two-thirds of the dry-type transformer. So, unless there are fire requirements to choose dry.