3W Transformers

[nightfox1925]

This may sound simple to others but I will take a shot in asking. What are the applications of a 3 winding transformers and when they are supposed to be applied. If three voltage levels pose as an advantage, wouldn't be suitable to use two winding transformers instead? What are the advantages and disadvantages?

GO PLACIDLY, AMIDST THE NOISE AND HASTE-Desiderata

 

[itsmoked]

That be one vague question... You want vague answers?

How about a concrete example so we can provide a worthy answer. Hmmmmmm?

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[dpc]

The two main advantages:

Economic - one three-winding transformer can do the work of two two winding transformers in many situations. On a $/kVA basis, the 3-winder will be less expensive (for large kVA ratings).

Short circuit ratings - splitting the low side into two windings will reduce the available SC current and can help in some situations.

You can also get two different voltages on the secondary and tertiary windings.

On paper, they can look pretty attractive, but they are tough to replace when they fail and a single failure will generally knock out more of the system.

 

[nightfox1925]

Thanks DPC, no wonder I only see these types on electric utilities ranging from 69kV~230kV here in our area and they call them auto-transformers. I have seen one wherein the secondary is further splitted into two windings and the tertiary is left hanging and they claim that this will damp harmonics and circulating currents.

May I ask any refence or link that would give me a deeper view on this? Thanks

GO PLACIDLY, AMIDST THE NOISE AND HASTE-Desiderata

 

[davidbeach]

and they call them auto-transformers

Three winding and auto-transformer are not the same thing at all, except that nearly all power system auto-transformers include a third winding as a delta tertiary. You can have three windings and not have an auto-transformer. Generally a step of one or two standard voltages (up to about 3:1 on voltage) will be auto-transformers for economic reasons. Larger voltage steps typically are not auto-transformers.

An industrial buck/boost transformer is a two winding auto-transformer.

 

[Skogsgurra]

You say "the secondary is further splitted into two windings and the tertiary is left hanging and they claim that this will damp harmonics and circulating currents"

And that is so. If there are two Y windings, your triplene harmonics have a high impedance that creates problems. Putting a tertiary D winding "hangning" makes the triplenes seeing a low impedance (3x120=360, so a D winding is a short to them). And that helps a lot. But this is only necessary if you have primary and secondary in Y. Usually, you have a primary D and a secondary Y. Then, the tertiary is not needed.

Gunnar Englund

http://www.gke.org

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