The per-phase equivalent circuit shown in Figure 13.2.6 of a three-phase, 600-V, 60-Hz, four pole, wye-connected, wound-rotor induction motor has the following parameters: R1 = 0.75 Ω, R'2 = 0.80 Ω, Xl1 = X' l2 = 2.0 Ω, and Xm = 50 Ω. Neglect the core losses.
(a) Find the slip at which the maximum developed torque occurs.
(b) Calculate the value of the maximum torque developed.
(c) What is the range of speed for stable operation of the motor?
(d) Determine the starting torque.
(e) Compute the per-phase referred value of the additional resistance that must be inserted in the rotor circuit in order to obtain the maximum torque at starting.
