Question

Question 3
[9]
A 25 kW separately-excited dc machine is operated at a constant speed of 3000
r/min with a constant field current such that the open-circuit armature voltage is 125
V. The armature resistance is 0.02 ohm. Determine the following for a terminal
voltage of 128 V:
(a) Is this a motor or generator?
(1)
(b) The armature current.
(2)
(c) The terminal power.
(d) Power developed in the armature.
(e) Torque.
Final answer
Final answer
Final answer
Final answer
[12]
Question 4
A short shunt compound machine having terminal voltage 250 V delivers a load
current of 40 A. The armature, series field and shunt field resistances are 0.050,
0.040 and 1000 respectively. Calculate the following if there is voltage drop of 1V
per brush.
(a) The armature current.

Answer 1

The armature current, terminal power, and the torque will be 150A, 18750 watts and 59.67Nm respectively.

How to calculate the current?

From the information given, the armature current will be:

E = 128 - I(2/100)

125 = 128 - I(0.02)

I = (128 - 125)/0.02

= 150A

The terminal power will be:

= E × I

= 125 × 150

= 18750 watts

The torque developed in the armature will be:

= (18750 × 60)/(2π × 3000)

= 59.67 Nm

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