Consider a shunt-connected dc motor that has the magnetization curve shown in Figure. The dc supply voltage is VT = 200 V, the armature resistance is RA = 0.085Ω, the field resistance is RF = 10Ω, and the adjustable resistance is Radj = 2.5Ω. At a speed of 1200 rpm, the rotational loss is Prot = 1000W. Assume that the rotational power loss is proportional to speed.
a. With a load that demands a torque of Tload = 200 Nm independent of speed, determine the steady-state armature current.
b. Suppose that in starting this machine, the field circuit has reached steady state and the motor is not moving when power is applied to the armature circuit. What is the initial value of IA? Determine the starting value of the developed torque. Compare these values to the steady-state values from part (a).
c. What additional resistance must be inserted in series with the armature to limit the starting current to 200A? Find the starting torque with this resistance in place.
