AC series motors are used to produce the propulsion of the vehicle. This system uses AC voltage from 15-25 KV at a frequency of 16.7 (i.e. 162/3) or 25 Hz. This low frequency leads to give better performance and more efficient operation by the series motor. The low frequency operation of overhead line reduce the communication interferences. Also the reactance of the line is low at the lower frequency and hence the voltage drop in the line is reduced. Thus increasing efficiency and P.F .