Transformer Rating

Huh?

In some areas,the HT line is 220kv and they need 34.5kv,so they would need a stepdown transformer of 220/34.5kv.Others have 33kv on their HT line and they require 6.9kv,so they will demand for 33/6.9kv.Some has 6.6kv on their HT line and they need 0.433kv(ie 433v) they would need a stepdown transformer of 6.6/0.433kv.

Where i am the HT line is 33kv,and we need 415v,so we use 33/0.415kv step down transformer.Where i was previously,the HT line was 11kv,and we need 415v,so we used 11/0.415kv stepdown transformer.

It all depends on the power available presently in your area of operation.

Patrick Whowha

but why we choose 433v as a no load voltage and why not 440v, 445v and any other voltage?

Have you heard the term "No load voltage"

If YES then thats your answer.

If NO, dear friend you need to study the basics of transformer. Try J&P Transformer book. I consider it the best.

but why we choose 6.9kv, 34.5kv as a no load voltage why not 7.0 kv,36kv voltage as a no load voltage?

The extra voltages (emfs generated at the transformer or the OC voltages at the secondary) are to account for the expected drop in the transformer outlet at full load current to get your required voltages (33KV, 6.9KV or 415V)

These will be around 4-5% over the required secondary voltages (corresponding to the % impedance)