For supply on 25 kV, 50 Hz single phase, the suitable motor for electric traction is
Right Answer is:
DC series motor
The single-phase 25 kV, 50 Hz railway became a global standard because of rectifier locomotives with DC motors. Without them, the HVDC railway would have remained the standard and might have evolved into a 6000 V DC. railway25 kV alternating current electrification is commonly used in railway electrification systems worldwide, especially for high-speed rail. The advantage here is the use of the main 50 Hz grid systems instead of special low-frequency traction generating stations.
Although 50 Hz AC commutator motors were feasible it requires a large number of poles and brushes to limit the internal losses. It was possible to use AC motors (and some railways did, with varying success), but they have less than ideal characteristics for traction purposes. This is because control of speed is difficult without varying the frequency and reliance on voltage to control speed gives a torque at any given speed that is not ideal. This is why DC series motors are the best choice for traction purposes, as they can be controlled by voltage, and have an almost ideal torque vs speed characteristic. When taking traction power from industrial frequency supplies, d.c. series motors are preferred, fed through a rectifier, using a variable voltage from a tap changer (for rectifiers), or from a fixed-voltage winding on the main transformer (in thyristor control).
This dc supply is finally fed to the D.C series traction motor fitted between the wheels. The system of traction employing 25-kV, 50-Hz, 1-phase ac supply has been adopted for all future track electrification in India.