A separately excited DC motor drives a constant torque mechanical load. The armature resistance is 0.2Ω and the nominal armature current is Ia=74A. The nominal rotational speed of the motor is 1150rpm. The armature winding is supplied from a 220V DC source. Rotational losses can be neglected. a)the load torque when the machine draws the nominal armature current while running at the nominal rotational speed is 126.096N.m b) Under the same load, the field winding current is decreased by 20%. Calculate the new rotational speed. d) With the same load, the field winding voltage is increased back to the nominal value. If the armature winding voltage is decreased to 180V, calculate the new rotational speed. e) Sketch the motor and the load torque-speed characteristics for the conditions in a), b) and d). Indicate operating points (ω,T) in all three cases
A separately excited DC motor drives a constant torque
resistance is 0.2Ω and the nominal armature current is Ia=74A. The nominal rotational speed
of the motor is 1150rpm. The armature winding is supplied from a 220V DC source.
Rotational losses can be neglected.
a)the load torque when the machine draws the nominal armature current while running at the nominal rotational speed is 126.096N.m
b) Under the same load, the field winding current is decreased by 20%. Calculate the new rotational speed.
d) With the same load, the field winding voltage is increased back to the nominal value. If the armature winding voltage is decreased to 180V, calculate the new rotational speed.
e) Sketch the motor and the load torque-speed characteristics for the conditions in a), b)
and
d). Indicate operating points (ω,T) in all three cases
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