sci.physics.electromag

"a_plutonium"
>
> As far as I know, the superconduction state occurs only in DC current.

"If, on the other hand, the superconductor is to be used as an AC conductor,
we must consider another effect, namely that the superconductor of type III
shows a pronounced hysteresis for alternating currents above a certain
magnitude. The hysteresis leads to losses which to the outside are
manifested as ohmic losses dependent on the frequency and on the current.
Although the superconductor type II does not show complete hysteresis, its
magnetization curves do not coincide for a rising and a declining field, at
least in a range between H c1 and H c2 . Therefore, the superconductor of
type II also entails certain alternating current losses, though the losses
are slight, compared to the superconductor of type III. The type I
superconductor has even smaller alternating current losses. Despite this
fact, superconductors of type II are used to conduct alternating current,
since their slight alternating current losses are easily overcompensated by
their relatively high current carrying capacity."
It is from: http://www.freepatentsonline.com/3611078.html
S*