Milwaukee's Bipolars

Milwaukee Road EP-2, Seattle, August 26, 1961. I have just graduated from high school, and working at Bethlehem Steel in the Nut House, making good money to enter Washington State University next month.

Whilst making my “rounds” for the last time prior to moving to Pullman, I tripped over this Bipolar in her final agonizing hours at a scrap yard on the Duwamish waterway. What a sad sight – one can only remember her beautiful color scheme on the head end of the “Olympian,” designed to work the Cascade and Saddle Mountains.

These were unique electric locomotives in that the armatures were mounted on the axles, and two field poles, 180° apart, were mounted on the locomotive chassis. This resulted in zero wheel slip at throttle-up, and there was no horsepower lost in “gear trains.” And they lacked the growling gear sounds of the Box Cabs, and no traction motor whine. With a top speed of 458 RPM, the only noise they made was the bell and the horn!

The concept of the bipolar design - also known as the "s" motor, can be traced back to the 1890's, in English deep tube applications, as presented in this historical presentation.

The drive concept was original, but it did have flaws that made it a unique electric motor system not repeated.

The EP-2’s 12 - 1,000 volt traction motors, controlled by a 26 notch throttle, ran in SERIES, 250 volts to each motor, SERIES-PARALLEL, 2 groups of 6 motors in series, with 500 volts to each motor, LOW SPEED PARALLEL, 3 groups of 4 motors in series, 750 volts to each motor, and HIGH SPEED PARALLEL, with 4 groups of 3 motors in series, 1,000 volts to each motor.

At start up, a locomotive could deliver 123,500 pounds of tractive effort, requiring up to 6,000 amps, with running speed around 800 amps.

The locomotive consisted of three articulated segments, with the center section containing an oil fired boiler and water supply for passenger car steam heating. From what I understand, the fireman spent considerable time on the road fiddling with this unit!

Designed to run as a single unit, this was the power pack for the “Olympian” from 1919 through 1960! I cannot recall seeing these units running, as my “rail” outings were confined to weekends, and it would have taken a deliberate outing to stake out the Milwaukee’s passenger movements. How naive I was in those days!

Attempts to increase speed by tweaking the traction motors in the 1950’s, resulted in an onslaught of electrical problems that eventually lead to their demise. Only one unit of the five, E-2, was saved and is on display at the Museum of Transportation in St Louis.

Railroad Stuff: Chicago, Milwaukee, St Paul and Pacific E-1. Built by General Electric/ALCo, January 27, 1920. Original number was 10250, renumbered to E-1 in March 1939. 3,200 horsepower. Scrapped in September 1961.