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Anonymous Poster #1

Changing Transformer Usage

02/09/2012 10:54 PM

I have a Three phase Transformer, rating 1600 KVA, 22 KV (Star)/ 430 Volts (Delta). This was installed about 25 years back to step up the DG supply (3 phase, 430 Volts) to 22 KV, and feed to 22 KV distribution network. On 22 KV distribution network, there are few transformers of 22 KV/433 V, feeding to utilities containing single phase as well as three phase loads. This transformer was a part of backup arrangement.

Now I plan to use this 1600 KVA transformer as a distribution transformer. I will give 22 KV as input and want to use 430 Volts as output. But the LV side is delta connected having no neutral conductor.

Is it technically possible to change the windings as desired, and use the transformer? A small change in capacity (1600 KVA) can be accepted.

Is there any better solution other than rewinding?

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#1

Re: Changing transformer usage

02/10/2012 3:06 AM

Two possibilities spring to mind:

  1. Install a zig-zag transformer to provide the neutral
  2. Buy a replacement transformer with a star point that can be used as neutral.
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#2

Re: Changing Transformer Usage

02/11/2012 12:21 AM

How are you going to do voltage regulation(OLTC)?. Will your area code allow to use an earth connected to transformer body as neutral?.

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#3

Re: Changing Transformer Usage

02/11/2012 12:49 AM

Hi Anon

You can install a delta/star neutral earth reactor (compensator) on the LV side to provide a star point for for the neutral which also makes it possible to limit the earth fault for protection purposes.

If the transformer is to be operated in parallel with other transformers (not good on the secondary side) off the same MV bus then the characteristics (vector group, impedances) should match. This will prevent circulating currents which your protection won't like.

Also it may be a good idea to carry out a sweep frequency response analysis on a transformer of that age to ensure that you're not installing a unit which will not last too much longer. Doble Engineering can help you with this.

Good luck

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#4

Re: Changing Transformer Usage

02/11/2012 6:20 AM

Use a zig-zag tranformer to ground delta winding.

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#5

Re: Changing Transformer Usage

02/11/2012 8:20 AM

Install a zig-zag transformer to provide the neutral Imade it before to nutral to erect earth fault protection .

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#6

Re: Changing Transformer Usage

02/12/2012 6:17 AM

Trade in your old transformer and replace it with one that is correct for your application.

It may work out to be around the same price as any augmentation, be more reliable, efficient, simpler, take up less space, be faster to implement.... and not look like it was lashed together by a bunch of stingy students.

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