The
Pennsylvania Railroad's class FF1 was an American
electric locomotive, a prototype numbered #3931 and nicknamed "Big Liz". It was built in 1917 to haul freight trains across the
Allegheny Mountains where the PRR planned to electrify. "Big Liz" proved workable but too powerful for the freight cars of the time with its 4600 available horsepower and astonishing 140,000
lbf (620
kN) of tractive effort. Pulling the train it regularly snapped
couplers and when moved to the rear as a pusher its force was sufficient to
pop cars in the middle of the train off the tracks.
It had a
2-6-6-2 wheel arrangement in two half-
frames, connected in the center. Each frame had a pair of three-phase AC induction motors driving a
jackshaft through gearing and a spring drive;
side rods then drove the wheels. The jackshafts can be mistaken for an additional fourth axle but the "wheels" are cogwheels to transfer power from the motors to the jackshaft.
Three-phase power for the 4 massive motors was supplied from the single phase overhead supply via a large
rotary converter housed in the body of the locomotive. Combined rated output of the motors was 7,640 hp (5,700 kW), but the converter could only supply a short term 4,600
hp (3,400
kW) or a continuous 4,000 hp (3,000 kW). With three-phase induction motors there was no way to control the speed of the motors; changing the wiring of the motor poles allowed for two speed settings, 10.3 and 20.6 mph (16.6 and 33.2 km/h), which were considered enough to drag heavy freight trains up and down
steep grades.
Its intended use as an Allegheny climber never realized and its power too much for the
rolling stock in service at the time, Big Liz was sidelined until being cut up for
scrap in 1940.
Staufer, Alvin F.; Pennypacker, Bert (1962). Pennsy Power: Steam and Electric Locomotives of the Pennsylvania Railroad, 1900-1957. Research by Martin Flattley. Carollton, Ohio: Alvin F. Staufer.
ISBN978-0-9445-1304-0.