A 3-phase, 50 Hz, 4-pole, 400 V wound rotor induction motor has a stator winding D-connected and a rotor winding Y-connected. Assume effective turn ratio stator/rotor = 2/1 ( phase basis). For a rotor speed of 1440 rpm, calculate:
(a) the slip
(b) the standstill rotor induced emf/phase
(c) the rotor induced emf/phase at this speed
(d) the rotor frequency in (b) and (c)