Autotransformer and three phase transformer
This document discusses three phase transformers and auto transformers. It begins by explaining the construction of three phase transformers, including forced oil and air cooling systems. It then reviews the star and delta configurations for three phase circuits. Star connections have a neutral point while delta connections do not. The document also discusses typical three phase transformer connections like Y-zigzag and delta-zigzag. It explains that auto transformers have only one winding and are used for small voltage changes, with diagrams of step-up and step-down configurations. Finally, it notes that three phase transformers can be made from single phase transformers connected in banks or from coils on a single core with multiple limbs.
Autotransformer and three phase 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.
- 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