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| Comparison between Autotransformer and Two winding transformer |
Autotransformer
The autotransformer consists of only one single-coil winding which is used as primary as well as secondary windings. In autotransformer, primary and secondary windings are connected electrically as well as magnetically. The autotransformer can be used as a step up and step down transformer. The autotransformer is used for voltage variations in various applications such as dimmer stat in cinema halls etc.
In autotransformer, copper savings is more because only one winding is used and also transformation ratio is near to unity. The autotransformer has fewer losses in windings so autotransformers have better efficiency and better voltage regulation.
The main drawback of autotransformers is primary windings are not insulated from the secondary windings. So autotransformers are not used for interconnecting the high voltage system to the low voltage system because full primary high appears across the low voltage secondary side which is very dangerous for operating personnel. The autotransformer is used only for small variations in voltage.
Two winding transformer
The two winding transformers consist of the separate primary winding as well as secondary winding wounded in the magnetic core. In two winding transformers, primary and secondary windings are not directly connected to each other which is insulated from each other and magnetically connected to each other.
In two winding transformers, more copper is required for making the transformer because two separate windings are used in these transformers.
The two winding transformers are also used for step down and step-up transformers. These transformers are used for interconnecting the high voltage system to the low voltage system because primary and secondary windings are insulated from each other and primary high voltage does not appear across the low voltage secondary side during the fault. So two winding transformers are safe for operating personnel.
Comparison table between the autotransformer and two winding transformer
Autotransformer
Two winding transformer
In autotransformer, a part of the winding is common for primary as well secondary.
In two winding transformers separate primary and secondary windings are used.
In autotransformer, there are movable contacts are available.
In two winding there are no movable contacts. Two winding transformers are static devices.
The autotransformer is operate as a step-down and step-up transformer.
The two winding transformers are also operated as a step-up as well as a step-down transformer.
In autotransformer, copper saving is more because one winding is used as primary as well as the secondary winding.
In two winding transformer copper saving is none because two separate windings are used.
In autotransformer, we get variable secondary voltage.
In two winding transformers, we can not get any variable secondary voltage.
In an autotransformer, there is no electrical isolation between the primary and secondary windings.
In two winding transformers, electrical isolation exists between the primary and secondary windings.
The size of the autotransformer is very small because one single winding is used.
The size of two winding transformers is very large because two separate winding are used.
In autotransformer number of winding is one.
In two winding transformer number of windings are two.
The cost of an autotransformer is less.
The cost of two winding transformers is very large.
In autotransformer losses in winding is low.
In two winding transformer losses in winding is high.
In autotransformers, efficiency is very high.
In two winding transformer efficiency is very low.
n autotransformer voltage regulation is better.
In two winding transformer efficiency is poor.
The autotransformer is used as variac, starting of ac motors and dimmer stat.
The two winding transformers are used in power supply in transmission and distribution, welding machine, isolation transformer.
The autotransformer works on the self-induction principle.
The two winding transformer works on the mutual induction principle.
In an autotransformer, power is transferred partially by transformation and partially by direct electrical contact.
In two winding transformer power is transferred only by transformation.
In an autotransformer, less winding material is required.
In two winding transformers, more winding material is required.
In autotransformer starting current decreases.
In two winding transformers starting current decreases by 1/3 times.
In autotransformer excitation current is small.
In two winding transformer excitation current is high.
The autotransformer is more economical.
The two winding transformers are less economical.
The autotransformer is less costly.
The two winding transformers are more costly.
In autotransformer leakage flux and resistance are low.
In two winding transformer leakage flux and resistance are high.
In autotransformer, impedance is less.
In two winding transformer impedance is high.
Key Difference between autotransformer and two winding transformer
1. In autotransformer a part of the winding is common for primary as well secondary. In two winding transformers separate primary and secondary windings are used.
2. In autotransformer, there are movable contacts are available. In two winding there are no movable contacts. Two winding transformers are static devices.
3. The autotransformer is operate as a step-down and step-up transformer. The two winding transformers are also operated as a step-up as well as a step-down transformer.
4. In autotransformer copper saving is more because one winding is used as primary as well as the secondary winding. In two winding transformer copper saving is none because two separate windings are used.
5. In autotransformer we get variable secondary voltage. In two winding transformers, we can not get any variable secondary voltage.
6. In autotransformer, there is no electrical isolation between the primary and secondary windings. In two winding transformers, electrical isolation exists between the primary and secondary windings.
7. The size of the autotransformer is very small because one single winding is used. The size of two winding transformers is very large because two separate winding are used.
8. In autotransformer number of winding is one. In two winding transformer number of windings are two.
9. The cost of an autotransformer is less. The cost of two winding transformers is very large.
10. In autotransformer losses in winding is low. In two winding transformer losses in winding is high.
11. In autotransformer, efficiency is very high. In two winding transformer efficiency is very low.
12. In autotransformer voltage regulation is better. In two winding transformer efficiency is poor.
13. The autotransformer is used as variac, starting of ac motors and dimmer stat. The two winding transformers are used in power supply in transmission and distribution, welding machine, isolation transformer.
14. The autotransformer works on the self-induction principle. The two winding transformer works on the mutual induction principle.
15. In an autotransformer, power is transferred partially by transformation and partially by direct electrical contact. In two winding transformer power is transferred only by transformation.
16. In an auto transformer less winding material is required. In two winding transformers, more winding material is required.
17. In autotransformer starting current decreases. In two winding transformers starting current decreases by 1/3 times.
18. In autotransformer excitation current is small. In two winding transformer excitation current is high.
19. The autotransformer is more economical. The two winding transformers are less economical.
20. The autotransformer is less costly. The two winding transformers are more costly.
21. In autotransformer leakage flux and resistance is low. In two winding transformer leakage flux and resistance are high.
22. In autotransformer impedance is less. In two winding transformer impedance is high.