To determine the armature voltage required for a separately excited DC motor to deliver a torque of 2.5 N-m at 1400 rpm, we can use the torque-speed characteristic of the motor.
From the given information, we know that the motor runs at 1500 rpm under no-load with 200 V applied to the armature. At this point, the torque is zero.
To find the relationship between torque and armature voltage, we can use the following equation:
(V1 / V2) = (N1 / N2) * √(T1 / T2)
where:
V1 is the initial armature voltage (200 V),
V2 is the desired armature voltage,
N1 is the initial speed (1500 rpm),
N2 is the desired speed (1400 rpm),
T1 is the initial torque (0 N-m),
T2 is the desired torque (2.5 N-m).
Plugging in the values, we have:
(V1 / V2) = (1500 / 1400) * √(0 / 2.5)
Since the initial torque is zero, the term √(0 / 2.5) becomes zero.
Therefore, we have:
(V1 / V2) = (1500 / 1400) * 0
= 0
From the equation, we can see that V1 / V2 = 0, which means the initial armature voltage (200 V) must be reduced to zero to achieve the desired torque of 2.5 N-m at 1400 rpm.
However, none of the answer choices provided match the result of reducing the armature voltage to zero. Therefore, none of the given options accurately represent the armature voltage required in this scenario.
