A three-phase, wye-connected, four-pole, 400- V, 60-Hz, 15-hp synchronous motor has a synchronous reactance of 3 Ω per phase and negligible armature resistance. The data for its no-load magnetization curve follow:
(a) When the motor operates at full load at 0.8 leading power factor, determine the power angle and the field current. Neglect all losses.
(b) Compute the minimum line current for the motor operating at full load and the corresponding field current.
(c) When the motor runs with an excitation of 10 A while taking an armature current of 25 A, calculate the power developed and the power factor.
(d) If the excitation is adjusted such that the magnitudes of the excitation voltage and the terminal voltage are equal, and if the motor is taking 20 A, find the torque developed.