6.6 kV and 11 kV Transmission Line

25 kVA sounds way too podunk for this MV discussion....

25kVA? Is that all?

should it be around 135 kVA?

sks

Without the original poster specifying which one it is, there seems little scope for further comment in this thread.

i mean, the station transformer should be around 135 kVA,

Regs,

sks

this is for 2*1650 kVA hydropower plant in Nepal.

regs,

sks

Then at least 3.5MVA is needed.

The location is irrelevant.

As there is so much at issue with this thread, perhaps it would be better to start a different thread containing all the attributes needed to elicit a swift and comprehensive solution, and abandon this one?

I'm glad you can follow this thread PW, it makes no sense to me!!

It is difficult to follow as the original poster is 'in too deep'. The job needs to be farmed-out to a local specialist, and not designed by a CR4 Committee!

From your post, I am making the following assumptions:

1. The 25kVA is for house power (to run the generator and plant controls and protection).

2. You are able to choose whichever you want of the 6.6kV or 11kV to derive your house power.

3. You expect that at least one of the generators is going to be running all the time, or else all the lights go out.

You have not specified where the outgoing connection to the utility is, at 6.6 or 11kV.

Any critical control and protection equipment should be powered by DC anyway, from a battery bank. The charger for it would be run by house power. That way, even if the lights go out you have power for your controls, relays, and circuit breakers / switchgear to operate. Where you take the power to run these is incidental, but I would suggest it is best to pick a connection where utility power can run the charger and other AC loads if both your generators are shut down. If utility connection is at the 11kV level, then that will also give you house power when the main transformer is taken out of service for testing and maintenance (it has to be done occasionally!).

A transformer LTC cannot operate fast enough to deal with voltage fluctuations such as motor starts, etc. Typical tap changing delays result in the LTC changing for longer, slower "trend" changes in voltage level. Again, that's why critical equipment should run off DC.

Otherwise, without a single-line diagram to know how your plant is set up, it is hard to see what advantages or disadvantages each of the connections might have. You could choose either.