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Shell Type Transformer

Transformers are stationary devices which we can use to step up or down the voltage. They are made up of two coils which are electrically separated but magnetically linked through a low reluctance (magnetic resistance) path.
Construction-wise, we can divide transformers into two types
  1. Core Type Transformer
  2. Shell Type Transformer

A recent development is the spiral-core or wound-core type. Also 3-phase Shell-type transformer.

Core of Shell Type Transformer

We use ‘E’s and ‘L’s shape laminations to make the core of the shell-type transformer. We try to reduce the width of laminations as possible to reduce the effects of eddy currents. Core of Shell Type Transformer

Limb of Shell Type Transformer

Shell type transformer is made up of 3 limbs or legs which we can use to increase the mechanical strength of its core. Our windings are also well-protected from any mechanical damage due to the shell-type core.

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We wound the HV and LV windings around the central limb which will carry the whole flux (Φ), whereas the side limbs will carry half flux (Φ/2). Hence to accommodate the flux we design the cross-section of the central limb such that it is twice the size of the side limbs. transformer core limb The advantage we get over here is that magnetic flux can flow through two closed magnetic paths which will decrease the core losses generated and increase the efficiency of the machine. So, we tend to get more output from shell type when compared to core type.

Winding of Shell Type Transformer

We wind both the HV and LV windings longitudinally along the core alternately. We sandwich the HV coils between two LV coils as shown in the figure below. shell type transformer Since both HV and LV coils are wound together in the central limb, we tend to require less number of conductor for wounding shell type. We require more insulation material as they are sandwiched between each other which could give rise to short-circuits.

The design of shell-type is a bit complex compared to core-type due to its core structure and winding nature. We need to remove a large number of windings for better maintenance which makes it very hard for repair works.

Cooling System of Shell Type Transformer

We need to implement forced air or oil cooling as heat generated during working is not easily dissipated from windings since the core surrounds it.

Applications of Shell Type Transformer

We use shell-type transformers for low voltage applications and are usually used in power circuits as well as electronic circuits. We also use them when we require reducing our expenses as they have square or rectangular cross-sections.

Advantages of Shell Type Transformer

One of the main benefits we get using shell-type is that the core gives a good support against the electromagnetic forces that can occur between the current carrying conductors during the case of a short-circuit. They also tend to have large window area which can be used for the large no. of copper conductors which will be needed when used for low-voltage applications.

Disadvantages of Shell Type Transformer

We need special fabrication facilities for the construction of a shell-type due to its complexity which will lead to increase in manufacturing and labour cost.


KKALPESH KOTWAL commented on 13/03/2018
Useful information to have for non electrical person also.
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