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Anonymous Poster

Selection of transformer

09/20/2008 7:09 AM

Dear sir,

How to decide vector group of the transforemer for 230/11 Kv and 11/0.433 Kv applications? DYn11 or YY0 or any thing. and what are the benefits of the selection and why we go for the particular vector group? please Kindly clarify



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Anonymous Poster

Re: Selection of transformer

09/22/2008 7:51 AM

Dear Sir,

The 230 and 11 kV will be Y(Star)Y(Star) only with Solidly grounded neutral. 11 kV and 0.433 kV will be Delta/Star.

For EHT voltages for carrying High Voltage only Star configuration is adopted. For MV Volatge to carry high current Delta Configuration will be adopted. The Phase displacement depends upon the displacement of the Secondary phase windings with Primary Phase Windings.




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In reply to #1

Re: Selection of transformer

09/23/2008 8:35 AM

Thank You sir,

Good answer. Also, Kindly tell me the selection procedure for multiwinding transformer and please tell me that in which book or website I can understand detail about thes things.

Thanks & Regards,

T.Kailash Kumar

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In reply to #2

Re: Selection of transformer

02/10/2021 7:20 AM


Pick up the phone to a transformer manufacturer and discuss the application with that organisation with a view to obtaining a quotation.

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In reply to #1

Re: Selection of transformer

09/23/2008 10:58 AM

230KV appears to be Tamil Nadu Voltage.Rest of India it is 220KV.While star configuration for EHV is acceptable in all states of India In TamilNadu it is not.Cost of OLTC for Delta is very high compared to star.However in Tamil Nadu it is always Delta primary on customer's as well there own substation.

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Re: Selection of transformer

02/12/2021 1:41 AM


230kV winding should only be Star due to two reasons:

1) It is likely to be graded insulation to keep cost of transformer low.

2) The transformer will be with OLTC for tap changing and the OLTC cost will be higher if it were to be Delta.

The vector group for 230/11kV will depend on what is the configuration at 11kV switchboard. If it is paralleled with some other incomer etc. Also, the aspects like whether it is a power plant or an industry taking power from grid etc. as well as what is the standard of Grid authority to be studied.

I have seen Yy, Yd transformers specified in my experience.

11/0.433kV transformer is easy - it will be either Dyn11 or Dyn1. Which one will depend on the practice in that particular state.


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Re: Selection of transformer

03/07/2021 1:44 PM

The transformer you select must have a secondary voltage equal to the required supply voltage of the equipment, typically 120/240 VAC. ... The transformer you select must have a kVA rating equal to or greater than the load on the transformer.


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Re: Selection of transformer

03/10/2021 9:33 AM

This is just one convention. I think the major considerations are :-

  1. At very high voltages [also biggest kVA ratings] a direct earth on the winding (star) allows thinner insulation at earthed end of windings. Also auto transformers, commonly single phase, are economic for very high voltage.
  2. A delta winding reduces transfer of harmonics through transformer.
  3. Star windings give easy earthing of system.
  4. Each Delta winding has lower current than star, this makes them easier for HV side of transfo.
  5. It should be possible to parallel systems at same voltage or jump voltage levels, only possible with correct phase transformation.
  6. Withstanding short circuit faults and having the necessary leakage inductance to limit short circuit currents affect the lowest cost winding arrangement for each HV & LV level.

Practice for 60 Hz may be different, if only because they use shell type transformers rather than core type usual for 50Hz.

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