Electric
interurban and
trolley cars required 600
volts
direct current to operate a car's Direct Current (DC) traction motors. The function of a "substation" was to convert very high voltage
alternating current (AC) from a power generating plant (often miles away) for an AC to lower voltage DC conversion. The high voltage AC entered the substation, was dropped in level by a
transformer, and the resulting lower voltage AC was then fed to a device called a
rotary converter for the conversion to 600 volts DC. Substations existed on every trolley and interurban line in the United States and often still do for today's
subway and
light rail lines, although the very large and cumbersome rotary converter, as much as in diameter and rotating, has been replaced by
solid state converters. ==See also==