On Saturday, March 03, 2012 12:03:01 PM Przemek Klosowski did opine: > >> Anders, can You suggest, how to implement that (preferably a simple > >> and easy way, so that even child or golden retriever :) would > >> understand)? The scheme in my IRAMS datasheet suggests using Shunt > >> resistors for that, but I suspect that something else should also be > >> needed, but I have no idea, how these things actually work. > > In principle you could measure the current by attaching current > transformers or Hall sensors to the motor leads, avoiding the > high-side and high common mode voltage issues. The downside might be > speed/frequency response. What do people think about these > alternatives to resistive shunts? Excellent idea. Current transformers can have frequency response problems depending on the magnetic materials used. but are pretty accurate. Hall effect stuff is probably faster but from my experience, not as linear.
For this duty, either should be more than fast enough. One of the side effects of the current transformer will be a slowing of the Di-Dt under fault conditions, which may give enough time for shutdowns to be done. To me its advantageous when a $1 fuse blows instead of the $500 circuit. :) The current transformers output voltage will be very high under fault conditions, so figure on some sort of over-voltage protection in the circuitry its feeding so it doesn't get blown by a momentary carbon track as a June bug gets to meet its maker. Oh, and Kirchoffs applies to the delta connected circuit. Barring ground faults, sensing any 2 is sufficient. But around machinery, and in the real world, ground faults DO happen and I would design accordingly. IOW, sense all three phases. Cheers, Gene -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) My web page: <http://coyoteden.dyndns-free.com:85/gene> Lead me not into temptation... I can find it myself. ------------------------------------------------------------------------------ Virtualization & Cloud Management Using Capacity Planning Cloud computing makes use of virtualization - but cloud computing also focuses on allowing computing to be delivered as a service. http://www.accelacomm.com/jaw/sfnl/114/51521223/ _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
