Shell Type Transformer:
There are E's and L's shape laminations are used to make the core of shell type of transformer. the core of the single-phase transformer is made with three limbs or legs. the mechanical strength of the core is increased by this design and also improve the protection of transformer windings from external mechanical shocks or vibrations. The high voltage and low voltage windings are wound around the central limb.
In a shell-type transformer, the core encircles the windings of the transformer. the central limb of the core carries the entire flux and the side limb of the transformer carries half of the flux. Hence the width of the central limb is two times the side limbs. The mechanical strength of the shell-type transformer has more due to bracing as compared to the core type transformer.
The magnetic flux flows through the one closed path which reduces the core losses or iron losses of the transformer and hence increases the efficiency of the transformer. The high voltage and low voltage winding are wound on the central limb of the core. the low voltage windings are placed near to the core and high voltage winding are placed outside the low voltage winding. which is reduce the insulation cost between the low voltage winding and core.
The windings used in shell type transformer is sandwiched or disc windings. The high voltage coil is sandwiched between two low voltage winding coils. the quantity of conductors required for wounding a shell-type transformer is less as compared to core type transformer.
In a shell-type transformer, sandwiched type winding are used so insulation requirement is more. the windings are sandwiched on each other which will give rise to a risk of short circuit fault between the windings. This transformer is also called sandwiched type or disc type transformer.
If a fault occurs in the inner windings can only be attended to by removing all outer windings. so winding maintenance jobs are very hard in the case of shell-type transformers. The cross-section area of the shell-type transformer is rectangular in shape.
The forced ail cooling and forced oil cooling are required for shell type transformer. The heat generated in a shell type transformer can not easily dissipate from the windings due to the surrounding yoke and limbs. the lamination used for the shell type transformer is made from high-grade steel. The laminations reduce the eddy current losses and silicon steel reduces hysteresis loss and laminations are insulated from each other by enamel insulation coatings.
Advantages of shell type transfomer:
1. In shell type transformer core losses or iron losses are less.
2. In shell type transfomer efficiency is high.
3. In shell type transfomer less copper conductor required for construction so cost of transfomer is less.
Disadvantages of Shell type transfomer:
1. In shell type transfomer, maintenance job of windings are very hard.
2. In shell type transfomer, heat dissipation is not easy.
3. In shell type transformer more insulation required.
4. In shell type transformer natural cooling is not possible.
Core type transformer:
The core of a single-phase transformer is a single-window core and has two limbs only. The magnetic core of the transformer is made from L shape laminations and form a rectangular shape. The high voltage and low voltage windings are wrapped around the core. In the core type transformer, windings surround the core.
The high voltage and low voltage winding are divided into two parts and half parts of both the windings are wound on one limb and the second-half part of both the windings are wound on other limbs.
The low voltage winding is first wrapped on the core surface with sufficient insulations between the core and low voltage windings. After low voltage winding, high voltage windings are wrapped with sufficient insulation between the low voltage windings and high voltage windings. the windings used in core type transformer are square, cruciform and two or three stepped. In this way, both the limbs are covered with low voltage and high voltage windings.
The quantity of copper conductors required for making winding is more as compared to shell-type transformers because windings are placed on separate limbs or legs. The potential difference between grounded core and high voltage winding is very high so the insulation required between them is also more and insulation cost increase. so low voltage windings are placed near to the core and high voltage winding are placed above the low voltage windings.
The core type transformer is also called cylindrical winding transformer or core winding transformer because windings of core type transformers are arranged such way as one half of low voltage winding near to the core and one half of high voltage windings above the low voltage winding and its makes a concentric coil. the mechanical strength of the core-type transformer is less as compared to the shell type transformer. In the core type, transformer flux is equally distributed in two limbs. In a core-type transformer, leakage flux is more as compared to a shell-type transformer which affects the performance and efficiency of the transformer. If any permanent fault occurs in inner windings it is rectified by removing outer windings only. so maintenance of core type transformer is very easy as compared to shell type transformer.
Advantages of core type transformer:
1. In core type transfomer, there are two limbs so iron required for making core is less.
2. In core type transformer, maintenance job of windings are very easy.
3. In core type transfomer, heat dissipation is very easy.
4. In core type transfomer, less insulation required.
5. In core type transformer natural cooling is possible.
Disadvantages of core type transfomer:
1. In core type transformer iron losses are more.
2. In core type transformer efficiency is low.
3. In core type transfomer more copper conductor is required for making a windings so cost is more.
| Core type Transformer | Shell-type transformer |
|---|---|
| In a core-type transformer, the core surrounds the windings of the transformer. | In a shell-type transformer, windings surround the core of the transformer. |
| In core type transformers, laminations are cut in forms of L's shapes. | In shell-type transformers, laminations are cut in forms of E's shape and L's shapes. |
| Cross-sectional area of core in core type transformer is square, cruciform, two or three stepped. | The cross-sectional area of the core in a shell type transformer is rectangular. |
| In a core-type transformer, more copper conductor requires in the construction of the core because windings are placed in separate limbs or lag. | In a shell-type transformer, less copper conductor requires in the construction of the core. |
| The core type transformer is called a cylindrical transformer or a core winding transformer. The windings are arranged in concentric coil in core type transformer. | The shell-type transformer is called sandwich or disc type transformer because low voltage and high voltage windings are formed in a sandwich. |
| The core type transformer has two limbs. | the shell type transformer has three limbs. |
| The mechanical strength of the core-type transformer is less. | The mechanical strength is more because shell type transformer has bracings. |
| The core type transformer requires less insulation because the core type transformer has two limbs. | The shell-type transformer requires more insulation because shell type transformer has three limbs. |
| In a core-type transformer, flux is equally distributed in the two side limbs of the transformer. | In a shell-type transformer, the central limbs carry the whole flux and two side limbs carry half of the flux. |
| In a Core type transformer, high voltage and low voltage windings are placed in two side limbs. | In a shell-type transformer, high voltage and low voltage windings are placed in central limbs. |
| The Core type transformers have two magnetic circuits. | The shell-type transformer has one magnetic circuit. |
| In core-type transformer, losses are more because core type transformer has two magnetic circuits. | In shell-type transformers have losses have fewer losses. |
| In a core-type transformer, fewer windings are removed for maintenance. | In a shell-type transformer number of windings are required to remove for maintenance work. |
| The output of the core-type transformer is less because the core type transformer has more losses. | The putout id shell type transformer is more because shell-type transformer has fewer losses. |
| Natural cooling is possible in shell type transformer. | Natural cooling is not possible in a core type transformer. |
| Better cooling in core type transformer because more surface exposed to the atmosphere. | Natural cooling is not possible in the case of the shell-type transformer so fans are required for cooling. |
| The core type transformer is used for high voltage applications like power transformer and autotransformer. | The shell-type transformer is used for low voltage applications like the transformer used in electronic circuits. |
| The Better heat dissipation in the case of a core type transformer. | The windings are surrounded by the core so heat dissipation is not easy in shell type transformer. |
| In core-type transformer leakage reactance is not easily possible. | In shell-type transformer leakage, reactance is highly possible. |
| In core-type transformers overall efficiency is less due to more losses. | In shell-type transformers, overall efficiency is more due to fewer losses. |
Difference between the Core type and shell-type transformer
1. In a core-type transformer, the core surrounds the windings of the transformer. In a shell-type transformer, windings surround the core of the transformer.
2. In core type transformers, laminations are cut in forms of L's shapes. In shell-type transformers, laminations are cut in forms of E's shape and L's shapes.
3. Cross-sectional area of core in core type transformer is square, cruciform, two or three stepped. The cross-sectional area of the core in a shell type transformer is rectangular.
4. In a core-type transformer, more copper conductor requires in the construction of the core because windings are placed in separate limbs or lag. In a shell-type transformer, less copper conductor requires in the construction of the core.
5. The core type transformer is called a cylindrical transformer or a core winding transformer. The windings are arranged in concentric coil in core type transformer. The shell-type transformer is called sandwich or disc type transformer because low voltage and high voltage windings are formed in a sandwich.
6. The core type transformer has two limbs. the shell type transformer has three limbs.
7. The mechanical strength of the core-type transformer is less. The mechanical strength is more because shell type transformer has bracings.
8. The core type transformer requires less insulation because the core type transformer has two limbs. The shell-type transformer requires more insulation because shell type transformer has three limbs.
9. In a core-type transformer, flux is equally distributed in the two side limbs of the transformer. In a shell-type transformer, the central limbs carry the whole flux and two side limbs carry half of the flux.
10. In a Core type transformer, high voltage and low voltage windings are placed in two side limbs. In a shell-type transformer, high voltage and low voltage windings are placed in central limbs.
11. The Core type transformers have two magnetic circuits. The shell-type transformer has one magnetic circuit.
12. In core-type transformer, losses are more because core type transformer has two magnetic circuits. In shell-type transformers have losses have fewer losses.
13. In a core-type transformer, fewer windings are removed for maintenance. In a shell-type transformer number of windings are required to remove for maintenance work.
14. The output of the core-type transformer is less because the core type transformer has more losses. The putout id shell type transformer is more because shell-type transformer has fewer losses.
15. Natural cooling is possible in shell type transformer. Natural cooling is not possible in a core type transformer.
16. Better cooling in core type transformer because more surface exposed to the atmosphere. Natural cooling is not possible in the case of the shell-type transformer so fans are required for cooling.
17. The core type transformer is used for high voltage applications like power transformer and autotransformer. The shell-type transformer is used for low voltage applications like the transformer used in electronic circuits.
18. The Better heat dissipation in the case of a core type transformer. The windings are surrounded by the core so heat dissipation is not easy in shell type transformer.
19. In core-type transformer leakage reactance is not easily possible.
In shell-type transformer leakage, reactance is highly possible.
20. In core-type transformers overall efficiency is less due to more losses. In shell-type transformers, overall efficiency is more due to fewer losses.