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This set of Electrical and Electronics Engineering Multiple Choice Questions & Answers (MCQs) focuses on Electrical And Electronics Engineering Set 5
Q1 | A 220V DC series motor is taking a current of 40A. Resistance of armature is 0.5Ω and series field is 0.25Ω. What is the voltage at the brushes?
- 190v
- 210v
- 180v
- none of the above
Q2 | A 220V DC series motor is taking a current of 40A. Resistance of armature is 0.5Ω and series field is 0.25Ω. What is the back emf?
- 190v
- 210v
- 170v
- none of the above
Q3 | A 220V series motor takes a current of 35A and runs at 500rpm. Armature resistance of 0.25Ω and series field resistance 0.3Ω. If iron and frictional losses amount of 600W, what is the armature torque?
- 122.5nm
- 118.5nm
- 134nm
- 117nm
Q4 | A 220V series motor takes a current of 35A and runs at 500rpm. Armature resistance of 0.25Ω and series field resistance 0.3Ω. If iron and frictional losses amount of 600W, what is the shaft torque?
- 134nm
- 122.5nm
- 117nm
- none of the above
Q5 | The armature torque of a DC motor running of 800rpm is 99.3Nm and shaft torque is 93.3Nm. The iron and friction losses are__.
- 502w
- 400w
- 200w
- 300w
Q6 | A 4 pole, 250V series motor has a wave connected armature with 1254 conductors. The flux per pole is 22mWb when the motor taking 50A. Iron and friction lossses amount to 1000W. Armature resistance 0.2Ω, series field resistance 0.2Ω. What is the speed of the motor___.
- 200rpm
- 225rpm
- 175rpm
- 250rpm
Q7 | A 4 pole, 250V series motor has a wave connected armature with 1254 conductors. The flux per pole is 22mWb when the motor taking 50A. Iron and friction lossses amount to 1000W. Armature resistance 0.2Ω, series field resistance 0.2Ω. What is the output power in H.P.
- 14.08hp
- 21.67hp
- 9.48hp
- 11.72hp
Q8 | Which motor should not be used for centrifugal pumps?
- shunt
- series
- cumulatively compound
- differenctially compound
Q9 | If the applied voltage to a DC machine is 230V, then back emf for maximum power developed is ___.
- 200v
- 230v
- 115v
- 460v
Q10 | A DC motor runs at 1725rpm at full load and 1775rpm at no load. The speed regulation is _____.
- 0.047
- 0.029
- 0.076
- 0.015
Q11 | A 4 pole, 500V shunt motor has 720 wave connected conductors on its armature. The full load armature current is 60A and flux per pole is 0.03Wb. The armature resistance is 0.2Ω and contact drop per brush is 1V. What is the back emf?
- 352v
- 408v
- 474v
- 486v
Q12 | A 4 pole, 500V shunt motor has 720 wave connected conductors on its armature. The full load armature current is 60A and flux per pole is 0.03Wb. The armature resistance is 0.2Ω and contact drop per brush is 1V. What is the full load speed of the motor?
- 675rpm
- 522rpm
- 484rpm
- 576rpm
Q13 | The armature of a 4 pole shunt motor has a lap winding accomodated in 60 slots, each containing 20 conductors, if the useful flux per pole is 23mWb, the armature torque developed when the armature current is 50A is _____.
- 176nm
- 192nm
- 256nm
- 218nm
Q14 | The resistance of the shunt field winding as compared to series field winding is ____.
- less
- more
- the same
- none of the above
Q15 | The field winding of a machine designed for separate excitation is
- of the shunt field type
- of the series field type
- either of the two
- none of the above
Q16 | A shunt motor runs at 500rpm on a 200V circuit. Its armature resistance is 0.5Ω and the current taken is 30A in addition to field current. What resistance must be placed in series with armature circuit to reduce to speed to 300 rpm; the current in armature remains same.
- 4.24Ω
- 3.78Ω
- 6.74Ω
- 2.47Ω
Q17 | A 200V DC series motor runs at 500rpm when taking a line current of 25A.The resistance of the armature is 0.3Ω and that of the series field is 0.5Ω. If current taken remains constant, calculate the resistance necessary to reduce the speed to 350rpm.
- 2.16Ω
- 3.42Ω
- 1.56Ω
- 4.83Ω
Q18 | In a DC compound machine,
- shunt field winding plays dominent role
- series field winding plays dominent role
- either can play dominent role
- both play equally dominent role
Q19 | A DC shunt motor is rotating at 267 rad/sec and developing 57.2Nm of torque. How many kilowatts of mechanical power are developed?
- 9.8kw
- 15.3kw
- 17.8kw
- 11.2kw
Q20 | A 20HP DC motor has 89.3% efficiency at rated power. What are its total losses?
- 1787w
- 1232w
- 2184w
- 1572w
Q21 | By flux control method of speed control of a dc shunt motor, we can obtain speeds.
- above the normal speed only
- below the normal speed only
- above as well as below the normal speed
- none of the above
Q22 | By putting controller resistance in series with the armature of a DC motor, we can obtain speeds
- above the normal speed only
- below the normal speed only
- above as well as below the normal speed
- none of the above
Q23 | Motor starters are essential for
- accelerating the motor
- starting the motor
- avoiding excessive starting current
- preventing fuse blowing
Q24 | The only disadvantage of field control method for controlling the speed of a dc shunt motor is that it
- gives speeds lower than the normal speed
- is wasteful
- needs a large rheostat
- adversely affects commutation
Q25 | When quick speed reversal is a consideration, the motor preffered is
- synchronous motor
- squirrel cage induction motor
- wound rotor induction motor
- dc motor