What it is and where it sits
The ACS880-31-101A-5 is a 3-phase drive in the ACS880 platform, rated for 380-500 V input. Frame size 31 carries the active-front-end variant for regenerating overhauling loads back onto the supply bus rather than dissipating them as heat. On the rolling-mill deck this part earns its slot on the drives line rather than the soft-starters line because of that active front end: a 4Q torque profile on the strip reel holds tension on the interstand loop without dumping regen energy as heat into a brake resistor bank, and the harmonic profile keeps it from tripping the upstream PCC on a shared bus with the roughing-mill rectifiers.
Where this class gets specified
Drives in the Motors & Motor Controls / Drives / Motor Drives class are the variable-frequency units specified for process-line speed and torque control — pumps, fans, conveyors, extruders, and the winder/unwinder sections where regen energy and harmonic limits both matter on the same bus.