A 150-kW, 60-Hz, six-pole, 460-V three-phase wound-rotor induction motor develops full load torque at a speed of 1157 r/min with the rotor short circuited. An external non-inductive resistance of 870 mΩ is placed in series with each phase of the rotor, and the motor is observed to develop its rated torque at a speed of 1072 r/min. Calculate the resistance per phase of the original motor.