Inrush Current of a Power Transformer being Energized while online a Generator

[Engineer1916]

ET Family,
Does anybody have any experience energizing a power transformer by a temp generator with the breaker closed? Will there be a reduction in the inrush current because the generators voltage will rise from zero to nominal voltage and the transformer will not be supplied with the line voltage instantly rather it will see a voltage buildup from zero to nominal by the generator?

 

[crshears]

Please include drawing; not sure what you're asking

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[RRaghunath]

Yes, it is a common practice to build-up generator terminal voltage with transformer connected in order to go easy on generator voltage controller as it is not to supply the transformer inrush current.
I see no problem.

 

[Engineer1916]

RRaghunath,
DO you know of any paper, or other document on this? I cant seem to find anything online.

Muhammad Siddique

 

[beyond86]

Yes, sure. We use the same method on our islanded power station. As Raghunath mentioned, we usually smoothly increase excitation current from zero and inrush current doesn't appear in this case.

 

[edison123]

"Will there be a reduction in the inrush current because the generators voltage will rise from zero to nominal voltage and the transformer will not be supplied with the line voltage"

You have answered your own question. Transformer inrush happens when there is a mismatch between the voltage cycle and the transformer flux cycle when the breaker is closed. Since you are starting from the zero or very low generator residual voltage with the breaker closed, there is no / very low voltage and hence no inrush. This is how large generator transformers, which usually do not have any breaker in-between because of large rated currents, are energized. It's somewhat similar to VFD start of the motors.

Muthu

http://www.edison.co.in

 

[crshears]

Does anybody have any experience energizing a power transformer by a temp generator with the breaker closed?

Which breaker? Do you mean generator output being sent direct to the low voltage terminals of the transformer but with the high side breaker open? If yes, then what beyond86 said

large generator transformers, which usually do not have any breaker in-between because of large rated currents

applies; I was an operator for six years in an eight unit 300 MW per power plant, and saw this done too many times to count.

Or do you have in mind placing an entire small distribution system on potential at once but without picking up any load?

Better information yields better answers.

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]