Tranformer

"Why don't you do your own home work". This statement is an example of someone who does not have all the facts. How does one know the author did not do his home work? It could be, the author is asking for confirmation, for what ever reason, he asked the question. Again, I am astonished by the lack of courtesy extended to those who take the time to log in and ask a question, then find someone actually takes the time to send a statement without substance!! There's one minute we will not get back. Is this site made for those who criticize others, or for those who spent much of their lives learning and perfecting their professional endeavors, to become better persons, and able to help others? Is there such a thing as a dumb question? We as a community need too apologize, to the author of the question, for those who are less considerate of others! I do apologize!

Dear,

1. Because in the MV levels (generated voltage) require less insulation level than for the HV & EHV. So, "Delta" windings are normally used in MV levels. By the way this is not applied to IPP only but in all power plants.

2. The secondary side of the step-up transformer is the HV side (e.g. 110, 132, 220 kV, etc.); accordingly, higher levels of insulation are required for the windings; so, that is why in HV & EHV levels "Star" windings are adopted.

3. There is a difference in the characteristics of the upper and lower current transformers; therefore, under normal operating conditions the current through the relay will not be zero. So, the bias coil which known also as (restrain coil) is used to avoid incorrect operation of the differential relay due to mismatch in current transformers and during external faults.

Regards,