Its an aircraft load bank, primarily used to test the Jet engine driven Generators , some went as high as 400 amp , all run at 28 volt 400 hrtz to my knowledge, It can also be used to load bank ground Support equipment , ie generators for aircraft running at 400 hrtz, Good example would be a dash 60 or the electrical on the E4 b (747 ) NECAP the dooms day 747 the president uses. It has HUGE power requirements as did the RC 135 series , EC 135 and the UC 135 stickle back radio relay series. One would have run the engines on the aircraft and the load bank was used to put a load on the systems to find a bad buss or a wonkey Generator , Run times were variable might have been an half hour or 3 hours depending on the write up from the flight crew. Out put was steady regardless of Engine RPM , it is kept at a constant by the CSD (constant speed drive, for example on 99 % of modern jets , which used a 3 D "wobbler Wheel " to keep rpm out put stable at any rpm at idle 0r above , big exception was the F22 which paradoxicly is mostly 12 volt DC WHO KNEW A new one ran 100 to 200 K depending on the year and manufacturer, Nuclear Certified and some of the Missile stuff used on the Air Force Space Rocket programs is out of this world price wise.