Transformer Inrush Current

For one thing, it might be 110% instead of 10%, and even that may be too low of an estimate.

The obvious question is "why do you want to do this?"

Why is transformer inrush a problem?

With your system are you not powering up and synchronising the diesel engines and transformer with the 132kV side switch open (if it is capable of load switching) or downstream loads disconnected so you are not trying to switch into full load. I am assuming you are switching the transformer with a load capable 13.8kV switch.

The consultant that designed the system should have taken transformer inrush into account.

Wait, based on previous threads on CR4 are YOU the consultant?

this is an emergency requirement by a client for 2 months only, as the client needs to test his load.

i am just trying to support the client.

secondly, i have to supply power to 13.8 Kv side.

diesel power system the client requested is of 20 MW. i will have to provide 29 generators each of 1 MW @ 70% running load.

these generators will all be synced together and will supply to step up transformers which will step up 460v into 13.8 Kv.

that 13.8 Kv will be feed to 100 MVA transformer. i have to give a black start to system that is why considering inrush current for my system safety.

client have to test the load with our generators until unless he gets power from national grid.

i think i have made the picture clear.

As long as the generators are all synched properly and your only loading the generators to 70% full load AND the electrical system can handle the additional transformer inrush current then the generators should be adequate to supply the additional momentary transformer inrush current.

What's the customers load as black starting a large capacitive or inductive load could be a bigger inrush current problem than transformer inrush?

I suggest that you do much more research to find out where that thumb-rule was pulled out of. When you do you will find that what you list as 10% is actually 10X, that energizing via the low-side can be raise this to nearly 20X, that the type of transformer core affects the magnitude, as does the source reactance, and all this assumes that your transformer has no high-side load.

yes, regarding energizing current, its 10X, not 10%, typographical error you can say.

and no, at the moment of closing our main VCB, the load side of transformer will not be connect to any load. they will switch the load on after every thing gets normal in case any abnormality occurs.

load in this case is the induction motors, mostly driven by VFD.

Nice try on shifting blame to the typo, but no cigar, you used the 10% in your calculation of the inrush current. Do you honestly believe that your generation can really supply 50,000 to 100,000 amps of mostly reactive current, even if it's only until the transients die out?