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sunilji
Active Contributor

Join Date: Sep 2008
Location: Mumbai, India
Posts: 14

Auto Transformers

10/27/2008 10:45 PM

We have an incoming 11kV supply for our 10 acre site thru which we have installed 2 distribution transformers of 11/0.4kV, 1250 kVA and 11/0.4kV, 750 kVA at opposite ends. The contract demand with the utility company is 1300 kVA at present and we are keen to increase it to 1600 kVA due to expansion.

As per the norms of the electric utility co., loads above 1500 kVA are fed from 33kV feeder. We are in a fix as it would mean replacing the existing switchgear, cables and transformers.

We thought of installing a 33kV/11kV, 2000 kVA, Auto-Transformer to keep the existing system undisturbed and at the same time minimize cost and losses

Anybody sees any serious disadvantages in using Auto-Transformer for our purpose ?

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elect-ok
Power-User

Join Date: Sep 2008
Location: Jakarta, Indonesia
Posts: 104
#1

Re: Auto Transformers

10/28/2008 2:47 AM

only one !!

expensive in beginning investment.
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Current Maarey
Power-User

Join Date: Aug 2008
Location: East
Posts: 117
Good Answers: 6
#2

Re: Auto Transformers

10/28/2008 7:22 AM

A 33/11kV two winding transformer Power transformer to match your system voltage will be a better solution. Though costly than a single winding auto-transformer.

However, there is no problem in using a auto-transformer in case the utility company allows its system to be so connected. Keep in mind the problems of fault levels as seen by the two sides, grounding systems.

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Anonymous Poster
#3

Re: Auto Transformers

10/29/2008 3:53 AM

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nesubra
Guru

Join Date: Nov 2006
Posts: 729
Good Answers: 2
#4

Re: Auto Transformers

10/29/2008 9:22 AM

Capitalise the losses on the new auto transformer and see.We decided in a couple substations to leave the down stream undisturbed but after capitalization it was worth while to go in for new equipment

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sunilji
Active Contributor

Join Date: Sep 2008
Location: Mumbai, India
Posts: 14
#5
In reply to #4

Re: Auto Transformers

10/29/2008 12:37 PM

Thanks. We did that and found the losses are tolerable in case of Auto-Transformer as compared to Double Wound transformer. Economically, Auto Transformer is the right answer but not having installed large capacity auto-transfomers in the past, we are hesitant. What should be the vector group for the Auto-Transformer ?

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nesubra
Guru

Join Date: Nov 2006
Posts: 729
Good Answers: 2
#6
In reply to #5

Re: Auto Transformers

10/30/2008 1:21 PM

did u also consider the existing trf .losses while capitalising which will continue and compare with direct transformation?

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sunilji
Active Contributor

Join Date: Sep 2008
Location: Mumbai, India
Posts: 14
#7

Re: Auto Transformers

10/30/2008 7:45 PM

Yes. We considered the losses of 33/11 TRF in addition to 11/0.433 TRFs. The total losses in this case are slightly higher but the cost saving is substantial. Hence, the annual interest on the savings more than offset the additional cost due to slightly higher losses. Again, as I said earlier, the economics are favourable only when Auto-Transformer is used as the losses are much lower in this case.

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Users who posted comments:

Anonymous Poster (1); Current Maarey (1); elect-ok (1); nesubra (2); sunilji (2)

Previous in Forum: high frequency integrator   Next in Forum: Is it healthy to maintain the rated current for motor during running condition??
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