Question

(ii) A three-phase, six pole, 50 Hz synchronous machine has a synchronous reactance of 4 ? per phase and a terminal voltage of 2000 V. The field current is adjusted so that the excitation voltage is 2300 V at a power angle of 15°. For this operating condition, determine A. Stator current B. Power factor C. Output power D. Torque required to drive the machine. [ 6 marks] (b) A 150 kW, 460 V, 3-phase 3520 rev/min, 60 Hz induction motor has a locked rotor torque of 600 N-m and a locked rotor current of 1400A. Three resistors are connected in series with the line so as to reduce the voltage across the motor to 0.65 p.u. Calculate (i) The apparent power drawn by the motor under full voltage, locked rotor condition. (ii) The apparent power absorbed by the motor when the resistors are in the circuit. (iii) The apparent power drawn from the line with the resistors in the circuit. (iv) The locked rotor torque developed by the motor. [10 marks]

          (ii) A three-phase, six pole, 50 Hz synchronous machine has a synchronous
reactance of 4 ? per phase and a terminal voltage of 2000 V. The field
current is adjusted so that the excitation voltage is 2300 V at a power
angle of 15°. For this operating condition, determine

A. Stator current
B. Power factor
C. Output power
D. Torque required to drive the machine.
[ 6 marks]

(b) A 150 kW, 460 V, 3-phase 3520 rev/min, 60 Hz induction motor has a
locked rotor torque of 600 N-m and a locked rotor current of 1400A. Three
resistors are connected in series with the line so as to reduce the voltage
across the motor to 0.65 p.u.
Calculate
(i) The apparent power drawn by the motor under full voltage, locked rotor
condition.
(ii) The apparent power absorbed by the motor when the resistors are in the
circuit.
(iii) The apparent power drawn from the line with the resistors in the circuit.
(iv) The locked rotor torque developed by the motor.

[10 marks]

(ii) A three-phase, six pole, 50 Hz synchronous machine has a synchronous
reactance of 4 ? per phase and a terminal voltage of 2000 V. The field
current is adjusted so that the excitation voltage is 2300 V at a power
angle of 15°. For this operating condition, determine

A. Stator current
B. Power factor
C. Output power
D. Torque required to drive the machine.
[ 6 marks]

(b) A 150 kW, 460 V, 3-phase 3520 rev/min, 60 Hz induction motor has a
locked rotor torque of 600 N-m and a locked rotor current of 1400A. Three
resistors are connected in series with the line so as to reduce the voltage
across the motor to 0.65 p.u.
Calculate
(i) The apparent power drawn by the motor under full voltage, locked rotor
condition.
(ii) The apparent power absorbed by the motor when the resistors are in the
circuit.
(iii) The apparent power drawn from the line with the resistors in the circuit.
(iv) The locked rotor torque developed by the motor.

[10 marks]

Added by Josep J.

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