Superconducting electromagnet driver design considerations. - Page 1
Forum section: electronics / general

author: Mike Whitenton
author_rank: Newbie
timestamp: August 14, 2015, 10:45:39 am
content: Hi Dave,I've been wondering about circuit design considerations for future superconducting motors and voice coils.As Science and Engineering moves forward there will come a time when high temperature & possibly room temperature superconducting components become available. With this premise, it would be an interesting topic for perhaps Fundamentals Friday to review schematic changes contrasting existing vs superconducting driver circuits.Example: Most high power subwoofer amplifiers are designed with a minimum voice coil resistive property of the copper or aluminum as a few ohms. If a 0 ohm subwoofer were subsituted the amplifier would over current and either blow or trigger the short circuit protection function. So what changes would need to be made for the power output stages of an amplifier to deliver a properly performing voice coil?Electric motors often include protection diodes etc to protect against voltage spikes etc. When you have a super conducting motor winding what would need to be done to properly design a driver circuit for this type of motor so things won't get damaged by the 0 Ohm windings?I would find this very interesting from an engineering standpoint and could make for a nice episode for the channel.Thanks Dave.Mike Whitenton

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 14, 2015, 11:04:17 pm
content: What's peculiar is, both examples have two glaring problems with them:Voice coils sit around permanent magnets and pole pieces.Motor and transformer windings sit around laminated iron.If we had room temperature superconductors, it might be feasible to avoid the iron altogether:Permanent magnets could be replaced by precharged superconductors. But they might not be as powerful (the critical field at room temperature, for a critical temperature not much higher than room temperature, will be fairly small).Windings can be smaller and thinner, so we can put on more turns, compensating for the reduction in permeability. Windings can be interleaved, compensating for the increased leakage inductance (at some expense to isolation capacitance, though).The incentive to these, in any case, is reducing the physical size, and reducing the losses, both conduction and core losses, so that the operating temperature can stay as close to room temperature as possible.The interesting question becomes: even if RTS aren't capable of higher flux density than conventional methods, would they become worthwhile for most applications, and what would an optimal design look like?Such an example might be the coreless motor,https://en.wikipedia.org/wiki/Electric_motor#Ironless_or_coreless_rotor_motorwhich currently is optimized for acceleration only. An RTS version might be made with good enough specs that it's capable of delivering real power, at significant weight savings, if not volume savings (because volume is still necessary for the magnetic field density and curvature, even if for reasons very different from the conventional limitation of saturation).If we had very high temperature superconductors,everythingwould be absolutely blown out of the water, because we could get flux densities well over 1.5T without using cores, Halbach arrays or water cooling. But this seems somewhat unbelievable to me just yet.Tim

author: max666
author_rank: Frequent Contributor
timestamp: August 23, 2015, 11:44:16 am
content: "Superconducting Driver Circuits" a Fundamentals Friday topic, huh? I'm afraid Dave would be stroking a very long grey beard, when that Friday ever comes.But regarding 0 ohm subwoofers and 0 ohm motor windings, keep in mind that only the DC resistance would be zero, impedance and back EMF wouldn't be zero.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 23, 2015, 12:47:34 pm
content: BTW a more subtle characteristic of type II superconductors is they have nonzero AC resistance.The frequency dependency is obvious, at some point: in the optical range, no material suddenly becomes 100% perfectly reflective, upon crossing some special temperature. The maximum frequency has something to do with the Cooper pairs' binding energy (~meV), so that you wouldn't expect any superconductor to work very far into the THz range. And also at high temperatures, where thermal energy (at room temp, ~26 meV) does the same thing.Inbetween DC and that high frequency cutoff, other things can happen. Type I superconductors apparently don't do much, and remain extremely conductive into the GHz. Type II exhibit flux pinning, which looks much like magnetic hysteresis (and therefore loss), but concerning current flow paths and loops instead of magnetic spins. This is the reason magnets can be statically levitated over type II superconductors.Typical superconducting resonators, used for particle accelerators, consist of spun niobium tubes, cooled to about 2 K and filled with vacuum, and have Q factors in the 3 x 10^8 range, for resonators in the 100 MHz to 2 GHz range.I haven't heard of data on type II superconductors at AC. Likely they'd still be fine at line frequencies, but anything higher, I don't know.Tim

author: Unknown
author_rank: Unknown
timestamp: August 30, 2015, 10:33:34 am
content: For anyone interested this is the timeline for superconducting discoveries.And for something really neat out of Israel:They are using liquid nitrogen.