Step-Up Transformer

[kssschsekhar]

Dear Folks,
In one of the industrial systems, 33kV and 6.6kV voltage levels are being used by using 220/33kV and 33/6.6kV Transformers. In refurbishment project, 11kV supply is required. As there is no spare feeder available in 33kV level, we would like to derive 11kV supply from 6.6kV switchgear by providing 6.6/11kV Transformers. Pl. discuss pros and cons.
Advanced Thanks for your partcipation...

 

[kssschsekhar]

In this industrial system, voltage is stepping down in a sequenial order i.e.220/33kV ,33kV/6.6kV and 6.6/0.42kV. In this sequence, if we use 6.6/11kV transformer , we think, voltage stepping-up from 6.6kV to 11kV is not conventional or industrial practice.

 

[davidbeach]

Going from 6.6kV to 11kV could be done, but it would be rather unusual. Be more creative with your 33kV system; reroute an existing circuit from its present load and feed a new line up of gear, then feed the existing load and the new loads.

 

[slavag]

Hi Kssschsekhar.
Please give us a more information.
What is a size of 33/6.6kV trafo?
What is power demand for the 11kV, hou match bays you need at the 11kV swg, how match infeeds to 11kV?
For example, some crazy idea, replace your 33/6.6kV trafo to 3-winding trafo 33/11/6.6kV.
Best Regards.
Slava

 

[kssschsekhar]

It is good idea in using 3-wdg transformer. But client doen't want to disturb the existing configuration.
Rating of 220/33kV Transformer:100MVA
Rating of 33/6.6/6.6kV Transformer: 40/20/20MVA
Existing load on 6.6kV wdg: 12MVA
Estimated 11kV Load: 2.5MW@0.85p.f

Other than "unusal", I am looking for any technical constrains of using 6.6/11kV Transformer of this network configuration.

 

[slavag]

Hi.
I don't see any problem from electrical point of view.
Maybe, will extra losses, not more.
But...
You have check with factory technology connection between 11kV and 6.6.KV.
What I meant, loose of 6.6kV is loose of 11kV. What happened with end product. Are it same line of product?
Are it separated process?
Best Regards.
Slava

 

[kssschsekhar]

Both are not same line of products. Power from 6.6kV switchgear to 6.6/11kV transformer will be used as stand-by source with emergency diesel generator back-up for 11kV Unit switchboard of Generation unit.

 

[slavag]

Hi.
In this case: I don't see any problem.
From time to time I see in industrial such applications.
Used "old" substation or "low" level of voltage as stand-by source. Problem is only losses on stand-by trafo.
Good Luck.
Slava

BTW, to your other Q, one of big generator mnf., siaed, that in-rush of GSU is not a problem for generator.

 

[kssschsekhar]

Slavag and David: Thanks a lot for giving your opinions.

 

[bacon4life]

Assuming you have already checked that the voltage regulation/motor starting would be acceptable with extra impedance?