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The Chicago, Milwaukee & St. Paul Railroad built 22 substations to power it's 654 route miles of electrified lines in Montana, Idaho and Washington. The substations themselves were supplied by hundreds of miles of company owned 110KV 3 phase AC transmission lines. The substations converted this to 3000 Volt DC by means of motor generator (MG) sets before passing the power on to the overhead trolley. Here we will look at the equipment that was housed within the substations and also a bit about the operations of them.

The High Voltage control panel was the electrical heart of the substations.The substation operators controlled the line voltage,started and stopped the MG sets, and recorded power usage from these panels. This is the panel at East Portal. Photo Michael Sol©

The Motor Generator sets converted the supplied AC power to DC for transmission to the overhead trolley. In the center is the synchronous,600RPM, AC motor, while to the left and right of it are the 1500 volt DC generators. The generators were wired in series to have an output of 3000volts. In the 50's, many of the MG sets were modified to raise output to 3600 volts by shimming the "air gap",i.e. raising the field coils closer to the armature. This was done to combat line loses which sometimes drew the line voltage down as low as 2600 volts between the substations. Pictured are the MG sets at Primrose. These were the only green MG's on the system, painted this color by the operator there. All the others were black. Photo by Michael Sol©

Pictured is the transformer room at East Portal. The transformers were necessary to lower the supplied 110KVAC power down to 2300VAC for supply to the MG sets.At the time of construction in the teens, transformers designed for use outside were considerably more expensive than the indoor variety, explaining why all the Milwaukee substations housed their transformers indoors. Photo by Michael Sol©

This is the remote substation control panel at Primrose. From here, the operator could control the substations at Drexel and Tarkio remotely.Originally, all the subsations required 24 hour coverage,which entailed 3 operators at each location, including housing for them as most of the locations were fairly remote. In the 1950's the company started the remote control program to reduce labor costs.Generally, three substations were connected in the remote loop. One operator would be stationed at each location with a different work shift for each. This provided coverage in case of emergency or a malfunction of the system. Photo by Michael Sol©

Construction view of East Portal Substation. (Large image) Courtesy Michael Sol.

View of East Portal in the 1970's. Photo by Michael Sol.