Need a transformer(s) to go from 21.6 kV to 34.5 kV. 1

[NAZ55]

We are looking for a transformer(s) to go from 21.6 kV to 34.5 kV. Since this is not a common transformer, we are looking at using two transformers back-to-back, a 21.6 kV / 480 V. with a 480 V / 34.5 kV and each approximately 2500 kVA. Any suggestions on where we could locate a 21.6 kV transformer as this does not appear to be a common voltage outside of Texas.

 

[magoo2]

Using 2 transformers back to back looks pretty inefficient. You'd have twice the kVA and twice the impedance. Plus twice the losses and space required.

You want a ratio of around 1.6:1 (i.e., 34.5/21.6). I'd look for a transformer with higher voltages than you need but with a 1.6 ratio. It's possible you might find a standard rating this way, but I'm not sure.

Also, if you find something close, you can get fixed taps to adjust the ratio further.

 

[rob46]

is it possible to use autotransformer for this application?

 

[NAZ55]

I am looking for possible solutions / contacts.

 

[itsmoked]

is it possible to use autotransformer for this application?

You can but I think only if the low side's insulation is rated for the high sides voltage. An open of the common winding gets you the Full Monty downstream.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[slavag]

Hi.
Agree with Magoo2 and you Zazmat. Used two trafos back to back.
Regards.
Slava

 

[magoo2]

Have you checked with a transformer manufacturer on this? 34.5 kV is a standard transformer voltage rating. It's just the combination of 34.5 kV and 21.6 kV that makes it non-standard or something that is not off-the-shelf. Still they can make it and 1 transformer would be better than 2.

I'd try Cooper, ABB, GE-Prolec, Howard, etc. and see what they say.

 

[Zogzog]

Zazmat,

Liquid filled, dry, or cast coil?

 

[NAZ55]

Zogzog,

I would have to check on that, but do you know of any type that is available?

Thanks
Zeeshan

 

[dpc]

Check with Uptegraff:

http://www.uptegraff.com/

I think they would be happy to build you an autotransformer for the right price.

You might also look for a 20.8 kV transformer, which is a semi-standard voltage in the northwest US. The taps could probably get you to where you need to go.

 

[Zogzog]

We build custom cast coil transformers. We also have the largest supply of dry type in the US buy none that meet your spec, I doubt you will find one, I checked sunbelt for a oil filled, nothing close.

This will probally be a custom job if you dont want to use 2 units. If you want to use 2 I can provide those also but as mentioned above, not the best idea.

 

[apowerengr]

What is the desired winding configuration and what are the voltages you are providing (phase-to-phase or phase-to-ground)?

 

[cranky108]

A 115kv to 69kv transformer has a ratio of 1.66 which is close. And there are a few of these around.

Consiter your application for ground source. An auto transformer is a good option.

Interesting enough the phase to ground voltage for 34.5kv is about 20kv, or close to the Phase to phase voltage you are looking for.

 

[rbulsara]

You can specify any voltage you want for a transformer and the mfr will build it. I do not see anything special in 21.6 to 34.5kV transformer. Most MV tranformers are built to order any way.

As for being common, it take days to replace a commonly available one as well so if you are worried about that it needs to be addressed by redundancy in the design. I also agree that using two transformers in series is inefficent and wastes space as well.

 

[jghrist]

As indicated by rob46 and dpc, an autotransformer would be appropriate. Autotransformers have a higher relative advantage over two-winding tranformers when the voltages are close.

 

[rbulsara]

An autotranformer will also be a "special" animal and not common, the very reason OP cited to go with "common" transformer.

 

[slavag]

Hey.
I'm so sorry.
I read now again thread. My bad!!!! I meant: not used two trafo back to back.
Sorry again.
Regards.
Slava

 

[NAZ55]

Zogzog,
Do you have any contact info. I could forward to my folks?

 

[Zogzog]

http://www.cbsnuclear.com