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C. 6. Which of the following is correct when the slip-ring induction motor is at starting? Where R1, R2, X, and X2 are standing for the Resistances and Reactances of the equivalent circuit for the induction motor. a. Ri= X b. Ri= X2 R2 = X d. R2 = X2 7. Which of the following parameter in the equivalent circuit of induction motor is independent of the maximum torque of the induction motor? E2 b. 12 d. X2 8. Which of the following is electrically connected between the field winding and armature winding in a DC motor? Carbon Brushes and commutator b. Commutator and bearings c. Bearings and frame d. Frame and carbon brushes a. C. R2 a. a. 9. For a DC compound motor, the series field can provide: better starting torque b. better speed regulation c.maximum torque d. maximum speed 10. What will be happen firstly when a DC series motor is operated at no-load? a. Over speed b. Overload c. Overheat d. Stopped to run
1. Which of the following would be caused for the rotor in a 3-phase slip-ring induction motor when the resistance of the rotor windings is increased? a. Current increased; Speed increased b. Current increased; Speed decreased c. Current decreased; Speed increased d. Current decreased; Speed decreased Which of the following is the speed of the rotating field for the induction motor relying on? a. Supply voltage b. Supply current c. Supply frequency d. Supply power 3. When the rotor is at standstill, the slip equals to: a. 0 b. 0.5 c. 1 d.00 2. a. c. 4. Which of the following is the relationship between the Gross mechanical power, Pm and the Power transferred from stator to rotor, Pag: Pm=s. Pag b. Pon = 312R2(1-s)/s Pm = Pag/s d. P. = Pag/(1-s) 5. Which of the following test can determine the core loss resistance of an 3-phase induction motor? No-load b. Rated-load Full-load d. Locked-rotor Page 1 of 4 a. C.
Part B (Short Question): Total 2 questions, 30 marks per each question, total 60 marks (6 marks) 1. (a) State the relationship of power ratio of the induction motor among the: Power transferred from stator to rotor (Air gap), Pas; Gross mechanical power, Pm; and Rotor copper loss, Peu (b) The input power of a 380V, 3-phase, 50Hz, 4-pole squirrel- cage induction motor is 40kW and driving a mechanical load at a speed of 1440 r.p.m. The stator copper losses are 2kW. The friction and windage losses are IkW and the core losses are 2kW. Determine: i. The slips; ii. The airgap power Pag. (16 mark) (8 marks)