Dear all,
I want to wind a special inductor to provide a powerful and intense magnetic field (e. g. 1.4 Tesla). I need to wind 300turn around my core with the 10cm length. Also, I have to excite my inductor by 100amperes current to generate my required magnetic field. There are some questions that I need to know.
1- If I am able to excite the winding for 4-8sec and stop excitation for 1-1.5sec, can I use a low diameter wire in my application? If I can, which kind of wire do you propose?
2- Do you think I need to circulate water by means of special wires in my wires to cool them?
3- What kinds of challenges will I face in construction procedure?
1. If your winding has several layers the safe approach is to have no more than 4 A / mm2. In your case, that would mean a cross section of 25 mm2. Since your duty cycle of 8 s / (8 + 1) s (worst case) is not much less than 1, this still calls for 25 mm2. You will have about 17 to 18 turns per layer, so there will be about 18 layers. The usual choice is copper wire with an insulating varnish.
2. If there is not enough space for wire with 25 mm2, I would not fall back on pipes but insert some kind of flat spacers between layers in order to enable air or water to flow between the layers. Fanning air through the coil would be much simpler (but noisier), and you can easily reach 10 A / mm2 resp. wire with a cross section of 10 mm2 resulting in 28 turns per layer and 11 layers. If using water, you would need to encapsulate the whole coil in a watertight housing, and you would still need a heat exchanger (probably with fan) unless you use fresh water instead of water in a closed circuit.
3. I guess if you do it yourself the first challenge is to bring the thick wire into the form of a regular coil. I would try to build some "wrap mechanism" with a crank, and I would ask a friend or colleague to help.
P.S. The varnish will withstand the pressure which occurs during normal wrapping but you have to avoid shearing forces, and if you use a metal tool for pulling or bending, it should be covered by soft material.
Pipes I do not recommend at least for one reason: With copper pipes used for plumbing, the ratio of the cross sections metal / water is so small that the winding takes to much space; there are pipes for high hydraulic pressure with a better ratio but as far as I know there are none made from copper.
You have not mentioned if the exciting current will be DC or AC. If AC, its frequency must be known because there will be skin effect, causing increased loss.
You have also not mentioned the approximate size targetted.
I agree with Joerg that trying to use water cooled copper pipes will be lot more complicated while forced air cooling using a good quality industrial cooling fan will be simpler.
The exciting current is a DC current. I am trying to decrease the size of the winding as small as possible. Also, I ask the consumer to stop the excitation time for a minute. In other words, I can energize the winding in 8 seconds and stop excitation for 60 seconds. Does the stop time help me in the reduction of the wire size?
Thanks a lot for your points.
Sorry for the delayed reply as I was on a trip.
Yes, the stop time of 60sec after 8sec of on-time does help reduction of the size, but by how much, will be decided by the thermal time constant of the system to hold on to heat for what time. If the time-constant is about three times larger than the off-time, it doesn't help.
Try it out experimentally - that is the quickest way.
Plot the area product versus operating duty ratio curve for your designed converter fixing the other parameters of the converter. But, the optimal value and design aspect , the winding size should be same due to change of on-time of the excitation.
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