A 3-phase, 460 V, 6-pole, 60 Hz cylindrical rotor synchronous motor has a synchronous reactance of  and negligible armature resistance. The load torque, proportional to the square of the speed, is 398 N.m at 1200 rpm.
Unity power factor is maintained by excitation control. Keeping the V/f constant, the frequency is reduced to 36 Hz. The torque angle  is