Typically if there is DC specification for NH it is for about 50% of AC voltage rating.
Time constant has to do with inductive energy, large time constant implies big inductance in the circuit and large amount of stored energy.
Superconducting 1000 H inductor at 500A would store insane amount of energy and would blow NH or class-T fuses to smithereens. Any attempt to break the circuit would just result higher inductive ”kickback” voltage or emf. 100 kV at 500A over the class T fuse would be spectacular.
Typical DC battery system don’t have such inductances.
