How generator energize big transformer

[alexcflee]

Hi All,
I have an application for a 3MW 4160V 3Ph. 60Hz generator to energize a 10MVA step up tranasformer 4.16/27.6 Kv.
Can it be done ? If it can, what caution I should be awared ?
Appreciated for advise and comment !

 

[ScottyUK]

Can you couple the transformer and generator so they operate as a block, either permanently or through a circuit breaker which you can close before the machine runs up? If you can do this then the generator excitation system will bring the generator terminal voltage, and by implication the transformer LV winding voltage, gently and gradually so there will be no inrush. The downside of this is that you will need to sync across the HV breaker, which will require a bare minimum of two single-phase VTs located one either side of the sync breaker.

Your transformer should ideally have an LV delta winding.

You should carefully consider protection zones for overlapping unit protection schemes: gen diff, transformer biased diff, maybe an overall diff covering from gen neutral out to the HV breaker.


----------------------------------

If we learn from our mistakes I'm getting a great education!

 

[rbulsara]

It depends on a lot of factors and difficult to say. I know of installations where a 2MW gen comes on line first when a number of transformers are on line, whose total MVA exceeds the gen rating by a good margin, but there are no issues. There are long cables involved in between. Where as there is another site where a 2MW unit's differential occasionally trips while energizing a 2MW close coupled transformer.

Check the CT specifications and the protection scheme. If it is switched on after full voltage is developed, CT may saturate and certain generator differential relays, if provided, may trip. This may not happen every time as the inrush varies with the exact instant of closing on the voltage waveform.

If you build up the voltage with breaker closed, it may work better, like a reduced voltage start. Or you will have to be creative with your protective relay settings.

I hope this is a one off setup and not a regular setup that requires frequent energizing and de-energizing of the transformer.





Rafiq Bulsara

http://www.srengineersct.com

 

[edison123]

I don't see any problems.

Muthu

http://www.edison.co.in