Reaction time of eddy currents to change in magnetic flux
Reaction time of eddy currents to change in magnetic flux
(OP)
Hello there,
I have a question on finding the reaction time on eddy currents.
I have an electromagnet(iron core with coils wounded in slots on it). Its contained in a rotating part. The magnetising signal is a current ramp.When the magnetising current is increased at a very fast rate (rate of flux change is high)and decreased at the same fast rate. The maximum magnetic effect seems to happen at a point where the current is already decreasing.
the eddy currents increase as the rate of change of flux increases. Could you please tell me how can I relate the timing of change in the flux to the action of the eddy currents(It would be nice if i can predict when the maximum magnetic effect will happen for a particular rate of change of flux). Please refer figure thanks.
I have a question on finding the reaction time on eddy currents.
I have an electromagnet(iron core with coils wounded in slots on it). Its contained in a rotating part. The magnetising signal is a current ramp.When the magnetising current is increased at a very fast rate (rate of flux change is high)and decreased at the same fast rate. The maximum magnetic effect seems to happen at a point where the current is already decreasing.
the eddy currents increase as the rate of change of flux increases. Could you please tell me how can I relate the timing of change in the flux to the action of the eddy currents(It would be nice if i can predict when the maximum magnetic effect will happen for a particular rate of change of flux). Please refer figure thanks.





RE: Reaction time of eddy currents to change in magnetic flux
When you have a moving (rotating or sliding) magnet field in face of a conductor, the resisting force or moment initially increases with speed, reaches a maximum, then decreases and goes asymptotically to zero. A repelling force is also generated that steadily increases with speed and asymptotically goes to a maximum value. That's why this phenomenon is the basis for a concept of magnetically levitated high speed trains.
The changing flux in the electromagnet adds a variation to this phenomenon, that stays basically the same.
If you do a literature search for maglev trains and magnetic brakes, you should be able to find something useful.
prex
http://www.xcalcs.com : Online engineering calculations
http://www.megamag.it : Magnetic brakes for fun rides
http://www.levitans.com : Air bearing pads
RE: Reaction time of eddy currents to change in magnetic flux
Could you please look into the attached picture and tell me what are the possible reasons for the Torque to reach its maximum long after current ? ...Thanks
RE: Reaction time of eddy currents to change in magnetic flux
RE: Reaction time of eddy currents to change in magnetic flux
Take first your device with a constant current supplied to the electromagnet (perhaps you can test this). You'll notice that there's a rotating speed for which the resisting moment is maximum: it's lower at lower speeds, but also at higher speeds.
Your variable currents (with constant speed) create somehow an effect of changing speed. I'm not able to predict or explain quantitatively anything: a detailed calculation by FEM or an in depth analysis based onto the principles I recalled in the former post is required to explain.
prex
http://www.xcalcs.com : Online engineering calculations
http://www.megamag.it : Magnetic brakes for fun rides
http://www.levitans.com : Air bearing pads
RE: Reaction time of eddy currents to change in magnetic flux
The torque is measured using a torque sensor which measures the torsion on the shaft.the shaft has a rotating cylinder inside which the electromagnet is contained. I cannot send a pic of the device as the work is confidential.
RE: Reaction time of eddy currents to change in magnetic flux
Applied torque (from magnetics) = Inertial torque (from acceleration) + measured torque?
So then, when accelerating, applied torque does not equal measured torque.
RE: Reaction time of eddy currents to change in magnetic flux
RE: Reaction time of eddy currents to change in magnetic flux
I would like to know the relation between the rate of change of flux and the rate of change of the measured torqe...So indirectly the eddy currents come into picture. thanks