Core Type Transformer
In the core type transformer , the windings surround the laminated sheet steel core. Both the are divided and half of each winding is placed on each limb to reduce the leakage flux. Since insulation of low voltage (LV) windings is less, it is placed next to core and then high voltage (HV) winding is placed around the LV coil. In such an arrangement only one layer of HV insulation is required and repair of the HV winding, which is more liable to faults than the LV winding is easy and convenient. It is shown in Fig. (a).
Advantages of Core Type Transformer
- Core type transformer offers good mechanical strength.
- Core type transformer has the advantage of preventing condensed flux leakage and iron loss.
- Core type transformer is efficient for high frequencies.
Disadvantages of Core Type Transformer
- Core type transformer is not good to use outdoors.
- Core type transformer can be noisy.
Shell Type Transformer
In Shell Type Transformer, the laminated insulated sheet steel core surrounds the copper windings. The core is shown in Fig. (b). The entire flux pass through the central part sheet steel core, but outside this central core, it divides into two parts half going in each direction. Sandwich type winding is used in which the sections of the primary winding are sandwiched on between the sections of the secondary winding. This way the leakage flux is reduced to a very small value. To minimize the amount of If V insulation, LV coils arc placed adjacent to the sheet steel core.
Comparing, the core type transformer has a longer mean length of magnetic core and a shorter mean length of turn. The core type transformer has less cross section of iron and therefore a greater number of turns. Core type has more space for insulation, so it is preferred for high voltage. Shell type coils are better braced mechanically, so that they are less easily displaced by the high electromechanical forces that frequently develop during short circuits.
Applications : Shell type transformer is better for low voltage and large output. On the other hand core type for high voltage and smaller output.
Advantages of Shell Type Transformer
- Good short circuit strength
- Mechanical & dielectric strength is high
- Controlling of leakage magnetic flux is good.
- The cooling system is efficient
- Size of this transformer is compact
- Design is flexible
- It has a high seismic-withstand ability
- Easily transported
- These are protected from outflow magnetic flux.
- Wire size can be selected flexibly so that it prevents local heating.
- The windings of this transformer can be simply separated with the help of a sandwich coil to prevent the leakage.
Disadvantages of Shell Type Transformer
- shell type transformer needs special manufacturing services to design this transformer.
- shell type transformer uses more iron in construction
- shell type transformer is complex
- Manufacturing cost will be high due to labor cost
- We cannot provide natural cooling.
- Repairing of this transformer is not easy.
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