1.4 A DC generator has terminal voltage of 250 V and an induced voltage of 262 V when the generator is loaded. The brush drop is 1 volt per brush and the armature resistance is 0.03 ohm and the shunt field circuit resistance is 35 ohms. Neglect armature reaction and determine the following: (a) The load current. (4) (b) The power of the load in kW. (1) (c) The % voltage regulation. (1) 1.5 A 200 V DC motor develops a shaft torque of 15 Nm at 1200 r/min. If the efficiency is 80%, determine the following: (a) The output power of the motor in watts. (2) (b) The input power of the motor in watts. (2) (c) The supply current of the motor. (2) ELM216A/EMJ21AI-S1-2021 ________________________ ______________________ Examiner Moderator Page 5 of 8 1.6 A series motor runs at 800 r/min when the voltage is 400 V and the current is 25 A. The armature resistance is 0.4 ohm and the series field resistance is 0.2 ohm. Determine the following: (a) The constant of the motor. (2) If the speed decreases to 600 r/min, the torque increases by 32% and the field increases by 10%, determine the following: (b) The new armature current. (2) (c) The new field current. (1) (d) The new total resistance of the motor in ohm. (2) (e) The additional resistance inserted in series with the motor in ohm. (2) 1.7 A 350 V shunt motor runs at its normal speed of 720 r/min when the armature current is 90 A. The resistance of the armature is 0.3 ohm. Determine the following: (a) The kΦ1 of the motor. (2) If armature current is 45 A and a resistance of 0.4 ohm is connected in series with the armature and the shunt field remaining constant determine the following: (b) The new kΦ2 of the motor. (1) (c) The new speed of the motor in r/min. (2) If the current is 45 A and the shunt field is reduced to 75% of its normal value by increasing resistance in the field circuit, determine the following: (d) The new kΦ2 of the motor. (2) (e) The new speed of the motor in r/min. (2) ________________________ ______________________ 2.3 A 150 kVA, 2500/250 V, 50 Hz, single phase transformer has a no-load current of 0.75 A and a core loss of 850 W, when the high voltage side is energized at the rated voltage and frequency. Determine the following: (a) The core loss component of no-load current. (2) (b) The magnetizing component of the no-load current. (3) (c) The core loss resistance on the high voltage side in ohm. (2) (d) The magnetizing reactance on the high voltage side in ohm. (2) 2.4 A 3 kVA, 500/250 V, 50 Hz, step-down transformer has the following parameters: Re1 = 3.5 ohm, Xe1 = 4.5 ohm, Rc1 = 2.9 Kilo ohm and Xm1 = 2.4 Kilo ohm. The transformer is operating at full-load with a power factor of 0.71 lagging. Determine the following: (a) The full load primary current. (1) (b) The angle between the full load voltage and current. (2) (c) The % full load Voltage regulation of the transformer. (3) (d) The magnitude of the no-load current. (3) (e) The angle of the no-load current. (1) (f) The power factor of the no-load current. (1) (g) Is the power factor leading or lagging? (1) (h) The iron losses in watts. (2) 2.5 A 200 kVA, 440/11000 V single phase transformer has an effective impedance of (4+j9) ohm on the secondary side. Estimate the following: (a) The effective resistance in the primary side in mΩ. (3) (b) The effective reactance in the primary side in mΩ. (2) (c) The short circuit voltage on the secondary side. (3) ELM216A/EMJ21AI-S1-2021 ________________________ ______________________ Examiner Moderator Page 7 of 8 Problem 3 Three Phase Induction Motors [34] 3.1 Which of the following statements about three-phase squirrel-cage induction motor is false? (1) (A) It has no external electrical connections to its rotor. (B) A three-phase supply is connected to its stator. (C) A magnetic flux which alternates is produced. ( (1) (A) The speed of rotation of the magnetic field is called the synchronous speed. (B) A three-phase supply connected to the rotor produces a rotating magnetic field. (C) The rotating magnetic field has a constant speed and constant magnitude. (D) It is essentially a constant speed type machine. 3.3 This question refers to a three-phase induction motor. Which statements are false? (1) (A) The slip speed is the synchronous speed minus the rotor speed. (B) As the rotor speed is loaded, the slip decreases. (C) The frequency of induced rotor EMF's increases with load on the rotor (D) The torque on the rotor is due to the interaction of magnetic fields. 3.4 A 500 V, 6-pole, 50 Hz, three phase, 8.5 kW, star connected induction motor has a no load slip of 1.8% and full load slip of 4.5%. Determine the following: (a) The speed of the rotating magnetic flux in r/min. (2) (b) The no-load speed in r/min. (2) (c) The full-load speed in r/min. (2) (d) The frequency of the rotor curre
1.4 A DC generator has terminal voltage of 250 V and an induced voltage of 262 V
when the generator is loaded. The brush drop is 1 volt per brush and the
armature resistance is 0.03 ohm and the shunt field circuit resistance is 35 ohms.
Neglect armature reaction and determine the following:
(a) The load current. (4)
(b) The power of the load in kW. (1)
(c) The % voltage regulation. (1)
1.5 A 200 V DC motor develops a shaft torque of 15 Nm at 1200 r/min. If the
efficiency is 80%, determine the following:
(a) The output power of the motor in watts. (2)
(b) The input power of the motor in watts. (2)
(c) The supply current of the motor. (2)
ELM216A/EMJ21AI-S1-2021
________________________ ______________________
Examiner Moderator
Page 5 of 8
1.6 A series motor runs at 800 r/min when the voltage is 400 V and the current is 25
A. The armature resistance is 0.4 ohm and the series field resistance is 0.2 ohm.
Determine the following:
(a) The constant of the motor. (2)
If the speed decreases to 600 r/min, the torque increases by 32% and the field
increases by 10%, determine the following:
(b) The new armature current. (2)
(c) The new field current. (1)
(d) The new total resistance of the motor in ohm. (2)
(e) The additional resistance inserted in series with the motor in ohm.
(2)
1.7 A 350 V shunt motor runs at its normal speed of 720 r/min when the armature
current is 90 A. The resistance of the armature is 0.3 ohm. Determine the
following:
(a) The kΦ1 of the motor. (2)
If armature current is 45 A and a resistance of 0.4 ohm is connected in series
with the armature and the shunt field remaining constant determine the following:
(b) The new kΦ2 of the motor. (1)
(c) The new speed of the motor in r/min. (2)
If the current is 45 A and the shunt field is reduced to 75% of its normal value by
increasing resistance in the field circuit, determine the following:
(d) The new kΦ2 of the motor. (2)
(e) The new speed of the motor in r/min. (2)
________________________ ______________________
2.3 A 150 kVA, 2500/250 V, 50 Hz, single phase transformer has a no-load current
of 0.75 A and a core loss of 850 W, when the high voltage side is energized at
the rated voltage and frequency. Determine the following:
(a) The core loss component of no-load current. (2)
(b) The magnetizing component of the no-load current. (3)
(c) The core loss resistance on the high voltage side in ohm. (2)
(d) The magnetizing reactance on the high voltage side in ohm. (2)
2.4 A 3 kVA, 500/250 V, 50 Hz, step-down transformer has the following
parameters: Re1 = 3.5 ohm, Xe1 = 4.5 ohm, Rc1 = 2.9 Kilo ohm and Xm1 = 2.4
Kilo ohm. The transformer is operating at full-load with a power factor of 0.71
lagging. Determine the following:
(a) The full load primary current. (1)
(b) The angle between the full load voltage and current. (2)
(c) The % full load Voltage regulation of the transformer. (3)
(d) The magnitude of the no-load current. (3)
(e) The angle of the no-load current. (1)
(f) The power factor of the no-load current. (1)
(g) Is the power factor leading or lagging? (1)
(h) The iron losses in watts. (2)
2.5 A 200 kVA, 440/11000 V single phase transformer has an effective impedance
of (4+j9) ohm on the secondary side. Estimate the following:
(a) The effective resistance in the primary side in mΩ. (3)
(b) The effective reactance in the primary side in mΩ. (2)
(c) The short circuit voltage on the secondary side. (3)
ELM216A/EMJ21AI-S1-2021
________________________ ______________________
Examiner Moderator
Page 7 of 8
Problem 3 Three Phase Induction Motors [34]
3.1 Which of the following statements about three-phase squirrel-cage induction
motor is false? (1)
(A) It has no external electrical connections to its rotor.
(B) A three-phase supply is connected to its stator.
(C) A magnetic flux which alternates is produced.
(
(1)
(A) The speed of rotation of the magnetic field is called the synchronous speed.
(B) A three-phase supply connected to the rotor produces a rotating magnetic
field.
(C) The rotating magnetic field has a constant speed and constant magnitude.
(D) It is essentially a constant speed type machine.
3.3 This question refers to a three-phase induction motor. Which statements are
false? (1)
(A) The slip speed is the synchronous speed minus the rotor speed.
(B) As the rotor speed is loaded, the slip decreases.
(C) The frequency of induced rotor EMF's increases with load on the rotor
(D) The torque on the rotor is due to the interaction of magnetic fields.
3.4 A 500 V, 6-pole, 50 Hz, three phase, 8.5 kW, star connected induction motor has
a no load slip of 1.8% and full load slip of 4.5%. Determine the following:
(a) The speed of the rotating magnetic flux in r/min. (2)
(b) The no-load speed in r/min. (2)
(c) The full-load speed in r/min. (2)
(d) The frequency of the rotor curre
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