Selection of transformer

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.

Regards,

N.suresh

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

tkailashkumar@gmail.com

Stop.

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

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.

Kailash,

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.

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.

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.