There are number of type of transformer but on the construction basis there are two basic type of transformers, one is core type and another one is shell type. These two transformer are differentiate due to its winding position wound on the core.
Core Type Transformer:
The structure of core of this transformer is in the form of a rectangular frame made from cold rolled grain oriented sheet steel (C.R.G.O.) with thin silicon steel laminations, due to lamination eddy current loss will reduce. It provides a single magnetic circuit path as shown in figure.
The primary and secondary windings are uniformly distributed on two adjacent limbs of the core. Both the windings are of cylindrical shape and they are arranged in a concentric manner the Low voltage (LV) winding is place near the core and high voltage (HV) winding on over it.
Core of core type transformer made from number of stampings arranged in rectangular manner, two possible type of stamping for making its core is,
1) L-core stamping and
2) UI-core stamping
Characteristics:
Question: Draw core type transformer diagram and state any two characteristics of that transformer.
1. This type of construction is used for high voltage and high power transformer.
2. In this type of transformer the core has only one window.
3. The transformer is easy for repair.
4. Less mechanical protection.
5. Winding enclose the core.
6. Better cooling.
Shell Type Transformer:
The construction of a shell type transformer shown in figure. The primary and secondary windings are placed on the central limb of the core. The high voltage and low voltage windings are arranged in sandwich type.
This type of core provides double magnetic circuit and it provides a better mechanical support and protection for the windings. The material used for making core is same as core type transformer.
For assembled the core of shell type transformer number of stampings are used to making a perfect shape of core. There are three possible type of stamping are used for making its core is,
1) EI-core stamping
2) M-core stamping
3) TU-core stamping
Characteristics:
Question: State any two characteristics of a shell type transformer.
1) When the coils are to be open for repairs, a large number of laminations are to be dismantled.
2) Natural cooling is poor since the windings are placed on the central limb.
This type of core provides better mechanical protection to the windings.
3) More economical for low voltage and low power transformer.
4) The steel core surround a major portion of the windings.
5) It provides a double magnetic circuit.
Comparison of Core Type and Shell Type Transformers:
| Sr. No. | Core Type Transformer | Shell Type Transformer |
| 1. | It has one window | It has two windows |
| 2. | Windings surround the core. | Core surrounds the windings. |
| 3. | Cylindrical windings are used. | Sandwich type windings are used. |
| 4. | This transformer is easy to repair. | It is not so easy to repair. |
| 5. | Better cooling since more surface is exposed to the atmosphere. | Cooling is not very effective. |
| 6. | Less mechanical protection to the coils (windings). | Better mechanical protection to the coils (windings). |
| 7. | It has one magnetic circuit. | It has two magnetic circuits. |
| 8. | Average length of core is more. | Average length of core is less. |
| 9. | Area of cross section is less so more turns are required. | Area of cross section is more so less turns are required. |
| 10. | Repair and maintenance is easy | Repair and maintenance is difficult |
| 11. | Application: Low current, high voltage, high power | Application: High current, low voltage, low power |
| 12. | Type of stamping used: 1) L-core stamping 2) UI-core stamping | Type of stamping used: 1) EI-core stamping 2) M-core stamping 3) TU-core stamping |
Important Key
1) Silicon steel lamination about 0.35 mm thick for 50Hz.
2) Magnetic core made from cold rolled grain oriented sheet steel (C.R.G.O.).
3) Core type transformer required less iron but more Conductor material.
4) Concentric winding are used for core type transformer.
5) Sandwiched winding are used for Shell type transformer.
6) Communication circuits, core is made up of powder ferromagnetic alloy.
7) Magnetic circuit is made up of nonmagnetic material.
