Soft-start transformers

[Eng_Dfr]

Hi y'all,

Here's my problem :
I have several transformers (12 x 1.1 MW ; 20 kV/400 V) that must be energized by a diesel generator on the 20 kV side. They will be energized as the LV side is disconnected.
To avoid oversizing the genset, a soft-start can be made ; a genset with transformer of about 700 kVA is enough then.

About the process of the soft-start... the genset regulator is off at the beginning, then it goes on as soon as the genset speed has reached something closed to its nominal speed. From that time, the voltage rises gradually to energize the transformers.
What really happen in such case ? What is the value of the inrush from the transformers ? Is it simply avoided -> 7*In becomes 1*In max seen from the genset ?
(Of course there's cabling between the transformer but it's not necessary to answer the question)

Thanks for your attention...

 

[waross]

Just connect the transformers directly to the gen-set and let them come up with the gen-set.
The transformer voltage will rise as the gen-set voltage rises.
The UFRO feature of the AVR will avoid under-frequency saturation of the transformers.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[edison123]

You have a 20 KV diesel generator? Or you want to energize the 20 KV winding at 400 V? The latter is not an issue at all. What is the purpose of this?

Muthu

http://www.edison.co.in

 

[waross]

I took it as using a 700 KVA, 0.4 kV to 20 kV transformer to energize the 20 kV transformers from the gen set.
Testing?

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Eng_Dfr]

My question is do the soft-start dim the inrush or not ? and in what proportion ? It's not a matter of protection, it's a matter of understanding what is happening.
You took it perfectly, waross the transformers will "be energized by a diesel generator on the 20 kV side". Edison123, it's a case study.
It's just a matter of understanding...

 

[GroovyGuy]

do the soft-start dim the inrush or not ? and in what proportion ?
Yes it does, it is proportional (ie consider the xfmr as a constant impedance device during the inrush phase.)


"I have not failed. I've just found 10,000 ways that won't work." Thomas Alva Edison (1847-1931)