Answer / nilkanth tailor

COZ, TORQUE IS DIRECTLY PROPORTIONAL TO THE SQUARE OF THE
CURRENT...SO THAT THIER IS VER HIGH CURRENT PRODUCE IN THE
STARTING OF DC SERIES MOTOR...AND IT IS DIFFICULT TO
CONTROL HIGH CUURENT...SO GENERALLY D.C. SERIES MOTOR
GENERALLY USEB IN TRAIN...CAUSE TRAIN REQUIRE HIGH STARTING
TORQUE...DUE TO HEAVY LOAD

Answer / naveen

Torque is proportional to flux and current.

reason why starting torque is high in series motor only is:
in DC series motor, flux is also proportional to current since the field winding is series with DC motor.

and the reason why its high in start is :
in starting back emf is 0 . current=(V-Ef)/R when Ef is 0 current attains high value which decreases as the speed of motor increases and thus the Ef.

Answer / ubendran mv

In SERIES MOTORS, the field windings are connected in
series with the armature coil. The field strength varies
with changes in armature current. When its speed is reduced
by a load, the series motor develops greater torque. Its
starting torque is greater than other types of dc motors.
Its speed varies widely between full-load and no-load.
Unloaded operation of large machines is dangerous.

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