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Three Winding Transformer

03/07/2014 6:10 AM

Why a third winding ,delta connected, is used in larger transformers used for only one voltage level out put.

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#1

Re: Three winding Transformer

03/07/2014 8:43 AM

It is a three phase power transformer.

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#2

Re: Three winding Transformer

03/07/2014 8:58 AM

There are couple of different reasons for a third delta winding.

Generally, in large inter-connecting transformers and auto transformers, a delta tertiary is used to provide a circulating path for zero sequence currents.

If industrial applications, if the transformer is feeding a power electronic load, like a VFD, then one of the secondary would star & the other secondary would be delta, to even out the 5th & 7th Harmonics, generated by the power electronic load.

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#4
In reply to #2

Re: Three winding Transformer

03/07/2014 11:33 AM

Another use of a delta tertiary in large power station transformers is to provide station service power at a lower voltage for the controls, protection, and building loads.

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#6
In reply to #2

Re: Three winding Transformer

03/08/2014 3:09 AM

Dear electricalexpert,can you be more elaborate on how the 5th & 7th Harmonics, generated by the power electronic load, even out?Sincere thanks.

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#7
In reply to #6

Re: Three winding Transformer

03/08/2014 10:13 AM

Here is a link to help explain the use of transformers to cancel harmonics. Although this is from one particular manufacturer,the principles can be applied anywhere.

Read and learn.Good Luck

http://www.controlledpwr.com/whitepapers/ukphsta2.pdf

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#3

Re: Three Winding Transformer

03/07/2014 11:19 AM

Auto

Star star (not my drawing)

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#5

Re: Three Winding Transformer

03/07/2014 4:23 PM

Well...if you have three phase power coming in and you only need one phase out...then your system's designer chose what is probably the easiest way to complete the job (or had that transformer already).

A "third winding" on a Delta Transformer makes it a Delta Transformer...you know...like the Greek Delta:

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#8

Re: Three Winding Transformer

03/08/2014 12:06 PM

surely just the triplen harmonics (3rd 9th etc ) will circulate around the delta winding?

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