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Choose the correct answer: 1- In an induction motor, no-load slip is generally- (a) Less than 1% (b) 2% (c) 4% (d) 5% 2 A 3-phase 440 V, 50 Hz induction motor has 4% slip. The frequency of rotor current will be-------- (c) 5Hz (d) 2Hz (a) 50Hz (b) 25Hz 3- The efficiency of 3-phase induction motor is about. (a) 100% (b) 80-90% 4- A double squirrel-cage induction motor has (c),50-60% (d) Less than 50% (b) Two parallel windings in stator (a) Two series winding in stator (c) Two parallel winding in rotor 5- The rotor slots are slightly skewed in squirrel cage induction motor to (d) Two rotors moving in opposite direction (a) Increase the strength of rotor bars (c) Economize on the copper to be used' 6- Stable operation of an induction motor is (b) Reduce the magnetic hum and locking tendency of rotor (d) Provide ease of fabrication (a) Between zero slip and unity slip (b) Between zero slip and slip corresponding to maximum torque (d) Between slip corresponding to maximum torque and unity slip (c) Between 0.5 slip and 0.95 slip 7- Iron loss in the rotor of a 3-phase induction motor is negligible due to (a) Very low frequency of emf induced in the rotor (b) Very low emf induced in the rotor (c) Very low flux density in rotor parts (d) Constant magnitude of flux linking the rotor co 8- The starting current of a 3-phase induction motor is about ---------of its full load rated current (a) Half (b) Twice (c) 5 to 7 times 9- During plugging of an induction motor (a) Phase sequence is reversed (c) One phase is open circuited (d) 8 to 10 times (b) A dc source is connected to stator (d) Power is fed back to mains 10- Direct online (D.O.L.) starter is used for induction motors (a)Less than 5 h.p. (b) Less than 10 h.p. (c) Greater than 10 h.p. (d) For any capacity

Choose the correct answer: 1- In an induction motor, no-load slip is generally- (a) Less than 1% (b) 2% (c) 4% (d) 5% 2 A 3-phase 440 V, 50 Hz induction motor has 4% slip. The frequency of rotor current will be-------- (c) 5Hz (d) 2Hz (a) 50Hz (b) 25Hz 3- The efficiency of 3-phase induction motor is about. (a) 100% (b) 80-90% 4- A double squirrel-cage induction motor has (c),50-60% (d) Less than 50% (b) Two parallel windings in stator (a) Two series winding in stator (c) Two parallel winding in rotor 5- The rotor slots are slightly skewed in squirrel cage induction motor to (d) Two rotors moving in opposite direction (a) Increase the strength of rotor bars (c) Economize on the copper to be used' 6- Stable operation of an induction motor is (b) Reduce the magnetic hum and locking tendency of rotor (d) Provide ease of fabrication (a) Between zero slip and unity slip (b) Between zero slip and slip corresponding to maximum torque (d) Between slip corresponding to maximum torque and unity slip (c) Between 0.5 slip and 0.95 slip 7- Iron loss in the rotor of a 3-phase induction motor is negligible due to (a) Very low frequency of emf induced in the rotor (b) Very low emf induced in the rotor (c) Very low flux density in rotor parts (d) Constant magnitude of flux linking the rotor co 8- The starting current of a 3-phase induction motor is about ---------of its full load rated current (a) Half (b) Twice (c) 5 to 7 times 9- During plugging of an induction motor (a) Phase sequence is reversed (c) One phase is open circuited (d) 8 to 10 times (b) A dc source is connected to stator (d) Power is fed back to mains 10- Direct online (D.O.L.) starter is used for induction motors (a)Less than 5 h.p. (b) Less than 10 h.p. (c) Greater than 10 h.p. (d) For any capacity

Electricity for Refrigeration, Heating, and Air Conditioning (MindTap Course List)
Electricity for Refrigeration, Heating, and Air Conditioning (MindTap Course List)
10th Edition
ISBN:9781337399128
Author:Russell E. Smith
Publisher:Russell E. Smith
Chapter10: Contactors, Relays, And Overloads
Section: Chapter Questions
Problem 31RQ
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Choose the correct answer: 1- In an induction motor, no-load slip is generally- (a) Less than 1% (b) 2% (c) 4% (d) 5% 2 A 3-phase 440 V, 50 Hz induction motor has 4% slip. The frequency of rotor current will be-------- (c) 5Hz (d) 2Hz (a) 50Hz (b) 25Hz 3- The efficiency of 3-phase induction motor is about. (a) 100% (b) 80-90% 4- A double squirrel-cage induction motor has (c),50-60% (d) Less than 50% (b) Two parallel windings in stator (a) Two series winding in stator (c) Two parallel winding in rotor 5- The rotor slots are slightly skewed in squirrel cage induction motor to (d) Two rotors moving in opposite direction (a) Increase the strength of rotor bars (c) Economize on the copper to be used' 6- Stable operation of an induction motor is (b) Reduce the magnetic hum and locking tendency of rotor (d) Provide ease of fabrication (a) Between zero slip and unity slip (b) Between zero slip and slip corresponding to maximum torque (d) Between slip corresponding to maximum torque and unity slip (c) Between 0.5 slip and 0.95 slip 7- Iron loss in the rotor of a 3-phase induction motor is negligible due to (a) Very low frequency of emf induced in the rotor (b) Very low emf induced in the rotor (c) Very low flux density in rotor parts (d) Constant magnitude of flux linking the rotor co 8- The starting current of a 3-phase induction motor is about ---------of its full load rated current (a) Half (b) Twice (c) 5 to 7 times 9- During plugging of an induction motor (a) Phase sequence is reversed (c) One phase is open circuited (d) 8 to 10 times (b) A dc source is connected to stator (d) Power is fed back to mains 10- Direct online (D.O.L.) starter is used for induction motors (a)Less than 5 h.p. (b) Less than 10 h.p. (c) Greater than 10 h.p. (d) For any capacity
Transcribed Image Text:Choose the correct answer: 1- In an induction motor, no-load slip is generally- (a) Less than 1% (b) 2% (c) 4% (d) 5% 2 A 3-phase 440 V, 50 Hz induction motor has 4% slip. The frequency of rotor current will be-------- (c) 5Hz (d) 2Hz (a) 50Hz (b) 25Hz 3- The efficiency of 3-phase induction motor is about. (a) 100% (b) 80-90% 4- A double squirrel-cage induction motor has (c),50-60% (d) Less than 50% (b) Two parallel windings in stator (a) Two series winding in stator (c) Two parallel winding in rotor 5- The rotor slots are slightly skewed in squirrel cage induction motor to (d) Two rotors moving in opposite direction (a) Increase the strength of rotor bars (c) Economize on the copper to be used' 6- Stable operation of an induction motor is (b) Reduce the magnetic hum and locking tendency of rotor (d) Provide ease of fabrication (a) Between zero slip and unity slip (b) Between zero slip and slip corresponding to maximum torque (d) Between slip corresponding to maximum torque and unity slip (c) Between 0.5 slip and 0.95 slip 7- Iron loss in the rotor of a 3-phase induction motor is negligible due to (a) Very low frequency of emf induced in the rotor (b) Very low emf induced in the rotor (c) Very low flux density in rotor parts (d) Constant magnitude of flux linking the rotor co 8- The starting current of a 3-phase induction motor is about ---------of its full load rated current (a) Half (b) Twice (c) 5 to 7 times 9- During plugging of an induction motor (a) Phase sequence is reversed (c) One phase is open circuited (d) 8 to 10 times (b) A dc source is connected to stator (d) Power is fed back to mains 10- Direct online (D.O.L.) starter is used for induction motors (a)Less than 5 h.p. (b) Less than 10 h.p. (c) Greater than 10 h.p. (d) For any capacity
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