Let me try to answer this good question.
Let's forget about temperature troubles and suppose superconduction is perfect at any temperature (while it is not).
Let's suppose we made a close turn of superconducting wire and submerse it in a pulse variable magnetic field impressing some amount of energy on the electrons inside the superconductor. This produce an electric charge movement called electric current. I think it is not necessary to recall that electric current is a charge movement not an electron movement, electrons doesn't move at light speed, charges do. Charges are photons electrons are matter. But, what do we have after the superconducting wire turn was excited by the magnethic pulse? A current inside it, and no voltage. Since power is current multiplied voltage and voltage is zero, we have no power dissipation and the current flows making a magnetic costant field as usual. Costant field does not induce power either. What is it? A permanent magnet. Till somehow, we draw the pulse energy we use to make the current run on the superconducting wire turn.
So we have ethernal (till the superconductin wire turn remains a perfect superconductor) but unusefull current. Current is no power, voltage is no power. Both are not energy. Current multiplied voltage is power, and power multuplied time is energy.
Cheers
Larry.