Not your 'C', my example of (C), whee I say there is a load on the magnet stirring space +, if your magnetic field is created through electric current, the load action of stirring space would be measured in a change of current since any load on the electric magnet would register.
I got your (C) of course, but as your (B) seemed to be a roundabout way of saying my (b), given my explanation why that's in fact a normal observation, and (C) is "(A) and/or (B)", that leaves your (A), which seems to be saying my (c).
...Eh?
Ok, there is an issue here with a true superconductor. Any voltage applied would create an infinite current. The question is 'Infinity + an added small # any larger'? Ok, you win this one, Infinity is Infinity according to math, you cant go higher (unless you enter the complex number plane and other mathematical tricks). I know you can add amps to your electromagnet, but will it be infinite? Having a DC superconducting electromagnet with say 100amp going through it, taking a second such magnet, bringing it into contact with the first, would that effect the charge in both charge superconducting magnets?
Oh dear! If you're stuck in DC terms, no wonder this mess is confusing.
Yes, the total DC voltage drop is zero, on a superconductor. The voltage and current are always finite.
If you transiently apply a voltage, the current ramps up. The coil has inductance! The instantaneous voltage can be nonzero, as long as you can supply the current demanded by the change.
Once charged, the current just sits there happily going around. It doesn't do any work. It does exert a magnetic field, but a static magnetic field does no work (for example, causing charged particles to move in an arc: momentum is exchanged, but not energy).
Or, you could even go so far as to say it's not a DC current at all. In the sense that, there is no resistance to define an L/R time constant, and therefore no cutoff frequency below which everything is "DC" and V = I*R, and above which is AC where we have to worry about reactance and waveforms.
And yes, there's always the good old nihilistic "no true DC" as long as the universe is finite, but for superconductors, that perhaps has a more practical side: the superconductor isn't thermodynamically stable in its environment, and will eventually be quenched somehow. (Well, here on Earth, where it's rather warm. In outer space, superconductors could persist for quite a while; but then, your concerns shift to as-yet-poorly understood loss mechanisms; cosmic ray damage eventually causing the superconductor to fall apart; or, back to nihilism, the heat death of the universe where everything ends up swallowed by black holes.)
In any case, when a superconductor is quenched, or brought down to zero current how ever -- it's done by applying the reverse voltage it was charged with. If this happens suddenly due to temperature, it's dissipated in the material (usually, superconducting wire is an intermetallic or ceramic phase embedded in copper, and the copper has both DC and AC losses -- which also limits charging speed, because the copper is a resistor in parallel with the superconductor, dissipating power into the cryostat until it's done), or in a huge arc if the circuit is broken*, or in a "flyback pulse" if it's discharged into a proper electrical load.
*I wonder if there's a video of this anywhere, hmm. Seems it's something they've thought of, at least:
https://www.hindawi.com/journals/mse/2008/359210/Unclear if it's been tested though. That would be a somewhat damaging test, seeing as they have MJ of energy in those coils!
Arrrrrggggg, my head is buzzing, since now, I'm beginning to think that the speed of approach of the 2 charged superconducting electromagnets, which cannot heat heat on their own, but we know such an action does affect electrical current in such a circuit.
Hmmm, interesting.
Well, let's see.
Suppose we approach a copper loop with a magnet. The loop has a gap cut into it, so we can measure the V and I there. The voltage is the EMF due to the change in flux in the center of the loop.
When the magnet approaches, the voltage spikes, then subsides (or, if the magnet continues through the center, it reverses and goes negative). The time integral of that spike is exactly the change in flux due to the magnet.
Suppose we short-circuit the gap, and measure the current. As the magnet approaches, it pushes against the loop, and a current is induced. If we hold the magnet inside the loop for a moment (some milliseconds, say), the current subsides -- it's dissipated by the copper's resistance.
Suppose, then, we cool the plate so that its resistance is very small. The same remains exactly true, but the time constant is merely longer: seconds instead.
If we replace copper with superconductor, then the current never dissipates, because there is no resistance to do it. (Uh, we'll suppose we're not using a conventional shunt resistor type current meter here.
)
So, suppose we have a superconducting ring that was charged with some current, then bring a magnet near it. The situation is identical: we've merely got a superposition, where there's an initial current, plus the induced current from pushing the magnet up to the loop.
So the current will go up.
( 
Don't ask why now I'm thinking this...) Now you got me thinking that a spinning a magnet at 6000rpm WONT create a 100hz the way I imagined. Maybe vibrating it back and forth 6000 times a second would be a much better candidate, all be it a weak one, generate EM waves, or like with a transmitting antenna, rapid oscillating the artificial magnet polarity back and forth along a fixed axis.
Sure, that works too. Or torsional vibration, say a magnet at the tip of a rigid shaft, twisting back and forth through a small angle. These give straight dipole (rather than circular omnidirectional) radiation patterns.
Tim
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