Starting currents when shifting speeds
Starting currents when shifting speeds
(OP)
Hi,
My facility has several two-speed squirrel cage induction motor fans that have occasionally tripped on thermal overload during shifts from fast speed to slow speed, and once from slow speed to fast speed.
I am trying to determine the starting/in-rush current during the three modes: stop-to-fast, slow-to-fast, and fast-to-slow.
Stop-to-fast mode data can be obtained from the vendor tech manual. But my electrical engineer is somewhat stumped when trying to figure out what the relative magnitudes would be for the other two modes, without going out in the field and measuring amps directly.
Thanks for any input. I just discovered this site, and plan to access it often. And I did try the search feature before posting...
Pat
My facility has several two-speed squirrel cage induction motor fans that have occasionally tripped on thermal overload during shifts from fast speed to slow speed, and once from slow speed to fast speed.
I am trying to determine the starting/in-rush current during the three modes: stop-to-fast, slow-to-fast, and fast-to-slow.
Stop-to-fast mode data can be obtained from the vendor tech manual. But my electrical engineer is somewhat stumped when trying to figure out what the relative magnitudes would be for the other two modes, without going out in the field and measuring amps directly.
Thanks for any input. I just discovered this site, and plan to access it often. And I did try the search feature before posting...
Pat





RE: Starting currents when shifting speeds
For slow to fast, the problem is less common. but again, a very short time delay would allow motor residual voltage to decay and avoid very high transients. With no motor terminal voltage, you would have an inrush that would not be greater than the normal starting current.
RE: Starting currents when shifting speeds
RE: Starting currents when shifting speeds
Motor sizes are not given, but there could be problems with similar high currents occuring during bus transfer. One paper is Amit Raje, et al, Bus Transfer Systems: Requirements, Implementation, and Experiences, IEEE Transactions in Industry Applications, Vol. 39, No. 1, January/February 2003
Spin-down characteristics of a momentarily open-circuited bus my contribute to the undesired operation.