Throughout this site the terms substation, transmission lines, and overhead are mentioned so it may be necessary for some explanation of terms.
The North Shore Line operated electrically powered trains, as opposed to steam or diesel. This meant that a considerable infrastructure was required to supply the power. As with most traction railroads, and the CTA in Chicago today, the trains operated on 600 volts DC current. This was picked up by the cars using trolley poles and overhead wire on most of the line and 3rd rail on sections in Chicago.
At the very beginning, many railroads generated their own power. The North Shore for instance, operated a large power station at their shops in Highwood. The problem with DC current is that it does not transmit well over long distances. There is a severe voltage drop, and so after many miles the voltage is much less than 600. AC, or alternating current can transmit very long distances with minimal voltage drop. The railroad thus generated DC current at Highwood to feed the lines, and generated high voltage AC current which was fed through transmission lines mounted onto the poles that held the overhead. At locations such as North Chicago, the railroad constructed substations. The high voltage AC current was put into a device known as a rotary converter. This was a large AC motor turning a DC generator. The generator would then output the 600 DC line current.
Eventually, it become too costly to generate their own electricity. It was much cheaper to purchase the now available commercial AC power. Power was purchased at certain locations along the line, stepped up to higher transmission voltage to overcome the voltage drop, and fed through the railroads transmission lines. Eventually over the years, more substations were added as the line was expanded. Because of the DC voltage drop, substations needed to be spaced every 3-5 miles along the line. The structures were large, brick buildings similar to the Edison station pictured here. The substations were modernized over the years also, with automated remote control systems installed in all substations, and new mercury arc rectifiers being installed to replace rotary converters in few other installations.
All substations on private right of way were dismantled after abandonment. Some of the buildings in various places remain, although the equipment is long gone.
