A separately-excited DC machine is operated at a constant speed of 3000 rpm and a constant field current such that the open-circuit armature voltage is 125 V. Given the armature resistance is 0.02 Ω and the terminal voltage is 128 V.
a) Determine whether the machine is a motor or generator. Sketch the corresponding equivalent circuit with proper labels and indicate the current direction. (10 marks)
b) Calculate the induced torque. (9 marks)
c) Determine the efficiency of the machine. (6 marks) [Total: 25 marks]