What is a Shell Type Transformer : Working & Its Applications

A transformer is an electrical device and it plays an essential role in transferring power from one circuit to the other. The electrical power transmission can be done with the help of an electromagnetic induction without changing frequency. But there is a change in magnitudes of current as well as voltage. The main function of the transformer is to step up and step down the voltage levels while using AC. The transformers are classified into two types like core type and shell type. The major difference between these two transformers is the arrangement of core and winding in the construction. In core type, the magnetic core includes 2-limbs & 2-yokes whereas, in shell type, it includes 3-limbs and 2-yokes. This article discusses an overview of shell type transformer, construction, working, advantages and its applications.

What is a Shell Type Transformer?

Definition: The shape of this transformer is rectangular and it includes three essential parts like one core and two windings which are shown in the following figure. It has two windings namely primary and secondary. The arrangement of these windings can be done in one limb. The coils of this transformer can be wounded in the form of the multi-layer disc where these layers are insulated through the paper from each other.

These transformers are used for high ratings and low voltage and cooling is not effective in this type of transformer. The winding of a shell-type transformer is distributed type, so that heat can be naturally dissipated. This transformer is also called a sandwich otherwise disc winding. Maintaining these transformers is difficult and mechanical strength is high. The cooling system used in the shell type transformer is forced air otherwise forced oil due to the surrounded winding through limbs and yoke.

Shell Type Transformer Construction

The arrangement of the laminations can be done with the shape of ‘E’ & ‘I’. These laminations are arranged opposite to each other so that high reluctance can be reduced at the joints. The alternating coats are stacked in a different way to get rid of the permanent joint.

This transformer includes 3-limbs; the middle limb holds the total flux whereas the side limb holds the flux partially. Therefore the middle limb’s width can be increased to the external limbs.

Here, both the windings of this transformer like low voltage and high voltage can be arranged on the central limbs. The low-voltage winding is arranged close to the core whereas the high-voltage winding can be arranged outside of the low-voltage winding. So that insulation cost can be reduced and it is arranged among the core as well as the low-voltage winding. The shape of these windings is cylindrical & the core laminations are placed on it.

Working

In this type of transformer, the two coils are twisted in the middle leg. Because in the two windings, one is wounded approximately in the center leg whereas the other one is wounded above it. So there is no possibility of leakage. Once the primary winding is excited, then it generates the flux so that it must cut the next coil. So while manufacturing the flux, it immediately cuts the next coil with less leakage to generate the required o/p voltage.

Advantages of Shell Type Transformer

The advantages are

• 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

The disadvantages are

• It needs special manufacturing services to design this transformer
• It uses more iron in construction
• It is complex
• Manufacturing cost will be high due to labor cost
• We cannot provide natural cooling.
• Repairing of this transformer is not easy

Applications of Shell Type Transformer

The applications are

• These transformers are applicable for low voltage applications which include electronic circuits as well as converters in power electronics.
• These are used where a small amount of voltage is required.
• The cost of this transformer used in low-voltage applications can be low due to the cross-section area core like rectangular or square.

FAQs

1). What is a shell-type transformer?

The rectangular transformer is known as a shell type where the windings of this are arranged within one limb.

2). Which are a better core type and shell-type transformer?

Shell type transformer is better due to fewer losses. So the output of this transformer is high.

3). Why is the transformer rated in kVA?

Because of the losses occurred within the transformer is independent for power factor, and this is the unit of apparent power.

4). What are the two main types of transformer?

They are shell type and core type.

5). Why the transformer is not used in DC?

Because of the constant and uniform magnetic field occurred within the primary coil, which will not pass to make an EMF within the secondary coil.

Thus, this is all about an overview of shell type transformer. These transformers are used in low voltage applications like electronic circuits & power electronic converters. This kind of transformer is a good choice compare with the core type. Here is a question for you, what is the difference between shell type transformer and core type transformer?