ECN Electrical Forum - Discussion Forums for Electricians, Inspectors and Related Professionals

Topic Options
Rate This Topic
#270 - 01/05/01 02:51 PM Transformer inrush current
Alan McNeil Offline
Member
Registered: 01/05/01
Posts: 18
Loc: Buzzards Bay, MA U.S.A.
Can anyone tell me what the inrush current of a 480/208 75kva transformer would be if it was typically loaded on the secondary side at around 135 amps? I know it goes way high, but I need a ball park figure for argument sake. My boss wants to know why they keep popping the breaker when the transfer switch goes back to normal power. I need a ball park figure
Top
Work Gear for Electricians and the Trades
#271 - 01/06/01 07:09 PM Re: Transformer inrush current
Bennie R. Palmer Offline
Member
Registered: 11/09/00
Posts: 72
Loc: Milwaukie, OR 97267 USA
Alan: I calculated the maximum inrush current for a 75 KVA transformer as 990 amps.
I do not know the duration. The secondary load is irrelevant for inrush calculations.
A circuit breaker with a time trip curve that will permit 990 amps, with a duration necessary to establish core flux, would be required for starting the transformer.
Top

Member Spotlight
Member Since: 12/24/00
Posts: 4259
New in the Gallery:
SE cable question
Featured:

2017 NEC and Related
2017 NEC
Now Available!

Shout Box


Who's Online
0 registered (), 55 Guests and 12 Spiders online.
Key: Admin, Global Mod, Mod
 
New in the Gallery:
SE cable question
 
Top Posters (30 Days)
Admin 47
HotLine1 43
gfretwell 19
Ruben Rocha 12
Trumpy 9
 
Newest Members
Scotto, Freecrowder, clee512, Jdscott2005, FAIZAN

ECN Electrical Forums - sponsored by Electrical Contractor Network - Electrical and Code Related Discussion for Electrical Contractors, Electricians, Inspectors, Instructors, Engineers and other related Professionals