A 480 kW, 50 Hz, 3.3 kV, eight-pole-pad wound-rotor induction motor has the following parameters referred to the stator: 0.65 Stator winding resistance: Rotor winding resistance: 0.50 Ω Stator leakage inductance: 10 mH Rotor leakage inductance: 10 mH Magnetizing inductance: 1040 mH (1) Calculate the synchronous speed of the motor. (ii) If the motor runs with a full-load slip of 0.03, calculate the full-load rotor speed. (iii) With the help of the equivalent circuit calculate the full-load stator current and its power factor.
A 480 kW, 50 Hz, 3.3 kV, eight-pole-pad wound-rotor induction motor has the following parameters referred to the stator: 0.65 Stator winding resistance: Rotor winding resistance: 0.50 Ω Stator leakage inductance: 10 mH Rotor leakage inductance: 10 mH Magnetizing inductance: 1040 mH (1) Calculate the synchronous speed of the motor. (ii) If the motor runs with a full-load slip of 0.03, calculate the full-load rotor speed. (iii) With the help of the equivalent circuit calculate the full-load stator current and its power factor. (iv) What is the full-load developed torque of this motor? (v) Calculate the efficiency of the motor on full-load if the core losses and the friction and windage losses are equal to 25 kW. Exte Pu THEN Wr 245 (vi) It is desired to start the motor with maximum torque using external resistors connected in series with the rotor winding. Calculate the resistance required to achieve maximum starting torque, and calculate the value of the resulting torque. (vii) (viii) By what factor does the addition of the external resistors increase the starting torque? { Calculate the starting current when the motor is started with the external resistance selected in part (vi) in the rotor circuit. (ix) By what factor does the addition of external resistors reduce the starting current?
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