LV Contactor selection for Transformer Switching
LV Contactor selection for Transformer Switching
(OP)
Can somebody help me in selection of LV contactor (starter) for Transformer switching?
NEMA ICS 2 Table 2-4-17 gives the max kVA ratings for Transformers with 1 to 20 times of Inrush current.
Now for a 600V, single phase application, max. kVA rating is given as 135kVA.
However, for us , we have a 150kVA Transformer which is Oil filled.
I suspect that the inrush current will not be as high as 20times.
Now the question : If I can get the exact inrush current value, can I select a Contactor which may be lower in size compared to what NEMA ICS 2 prescribes?
NEMA ICS 2 Table 2-4-17 gives the max kVA ratings for Transformers with 1 to 20 times of Inrush current.
Now for a 600V, single phase application, max. kVA rating is given as 135kVA.
However, for us , we have a 150kVA Transformer which is Oil filled.
I suspect that the inrush current will not be as high as 20times.
Now the question : If I can get the exact inrush current value, can I select a Contactor which may be lower in size compared to what NEMA ICS 2 prescribes?






RE: LV Contactor selection for Transformer Switching
But I would not assume the inrush will be less than 20x peak continuous current. This is a very real probability, depending on where (when) in the sine wave the contactor closes.
RE: LV Contactor selection for Transformer Switching
Please give your comments on this analysis. I am attaching some sample calculations of Inrush current from a Transformer handbook.