This PPT is about Three pahse Transformer its construction,Connection and about Auto-Transformer.

1. Three Phase Transformer And
Auto Transformer
Prepared By:
RITU K.R.
Assistant Professor (EE)
SISTec-E

2. 2
3- Transformer Construction
Left: A 1300 MVA, 24.5/345 kV, 60Hz transformer with forced oil
and air (fan) cooling.
Right: A 60 MVA, 225/26.4 kV, 60 Hz showing the conservator.

3. 3
3- Transformer Construction

4. SISTec-e 4
Review of balanced three
phase circuits
• Two possible configurations: Star (Y) and delta ( )
•Star has neutral, delta does not

5. 5
Star (Y) connection
•Line current is same as phase current
•Line-Line voltage is 3 phase-neutral voltage
•Power is given by 3 VL-LI Lcos or 3VphIphcos

6. 6
Delta ( ) connection
•Line-Line voltage is same as phase voltage
•Line current is 3 phase current
•Power is given by 3 VL-LI Lcos or 3VphIphcos

7. SISTec-e 7
Typical three phase transformer
connections

8. SISTec-e 8
Other possible three phase
Transformers Connection
• Y- zigzag
• - zigzag
•Open Delta or V
•Scott or T

9. The Auto Transformer
Sometimes, it is desirable to change the voltage by a small amount (for instance, when
the consumer is far away from the generator and it is needed to raise the voltage to
compensate for voltage drops).
In such situations, it would be expensive to wind a transformer with two windings of
approximately equal number of turns. An autotransformer (a transformer with only one
winding) is used instead.
Diagrams of step-up and step-down autotransformers:
Common
winding
Series
winding
Series
winding
Common
winding
Output (up) or input (down) voltage is a sum of voltages across common and series windings.

10. 10
Autotransformer
•Primary and secondary on the same winding. Therefore there is no
galvanic isolation.

11. 11
Features of Autotransformer
 Lower leakage
Lower losses
Lower magnetizing current
Increase kVA rating
 No galvanic Isolation

12. SISTec-e 12
How are three phase
Transformers made
• Either by having three single phase transformers connected as three
phase banks.
•Or by having coils mounted on a single core with multiple limbs
•The bank configuration is better from repair perspective, whereas the
single three phase unit will cost less ,occupy less space, weighs less and
is more efficient

13. Thank You
13