- Reasonable Assumptions May Be Proposed If Needed Not Permitted To Discuss Or Take Any Assistance Of Others Commutator 1 (177.76 KiB) Viewed 15 times
Reasonable assumptions may be proposed (if needed). Not permitted to discuss or take any assistance of others Commutator is used with DC machines to Convert AC current (A) Produce flux (C) to DC All of them (B) Decrease losses Series field winding in (D) DC machines has .... turns compared to shunt filed winding (A) Greater (C) Fewer (B) The same (D) Any of them If the lap winding of a 4-pole DC generator is reconnected as wave winding, the emf will be (A) Doubled (C) Halved (B) The same (D) Any of them At no load, the output voltage of DC series generator is (A) The rated voltage (C) Very small (B) Half the rated voltage (D) Any of them The DC motor than has high starting torque is 15 (A) Series (C) Shunt (B) Separate (D) Any of them The full load voltage is greater than the no load voltage in case of ...... cumulative compound DC generator 16 (A) Level (C) Over (D) A and C (B) Under The speed of DC motors is...... with the flux. (A) Directly proportional (C) Inversely proportional (D) Any of them (B) Not related Adding a resistance with the field of DC shunt generator results in ....... output voltage 18 (A) Higher (C) Zero (B) Lower (D) Any of them The output voltage of a DC shunt generator is very small in case of 19 (A) No residual flux (C) Low speed High field (B) (D) All of them resistance The DC motor than runs with very high speed if the load is disconnected is (A) Shunt (C) Compound (B) Series (D) Any of them 1- Answer ALL questions. Open notes and books 3- 2- 4- Question 1 (15 MARKS): Choose the correct answer A three-phase induction motor has 36 slots. The electrical angle of a slot 8se for 4-poles connection is (A) 15⁰ 1 11 (C) 20⁰ (B) 30⁰ (D) 40⁰ A 50 Hz three phase induction motor has 4 poles. The speed of the stator filed is: (A) 1500 rpm (C) 2 3000 rpm (B) 1800 rpm (D) 3600 rpm If the temperature of a three-phase induction motor is more than its insulation class maximum limit, the life time of the motor 3 (A) Increases (B) unchanged (C) Decreases (D) Any of them From methods of electrical breaking of three phase induction motors are..... braking: 4 (A) Plugging (C) Dynamic All of them (B) Regenerative (D) Using variable frequency drive (VFD) in the low- speed control range, the ratio V/F........ with frequency reduction 5 (A) Is kept constant (C) Increases (D) Any of them (B) Decreases When additional resistance is added with the rotor circuit of a wound rotor induction motor, the slip at maximum torque 6 Is constant (C) (A) (B) Decreases Increases Any of them (D) 7 The speed of three phase induction motor never reaches synchronous speed because.... will be zero. (C) Rotor EMF (A) Rotor current (D) All of them (B) Torque The full load speed is 1425 rpm for a 50 Hz, 4 poles three-phase induction motor. The rotor frequency at full load is....... 8 (C) 47.5 Hz (A) 50 Hz (B) 2.5 Hz (D) None of them Reduction in the input voltage of a three phase induction motor results in a reduction in 9 (A) Torque (C) Sm (B) Speed (D) A and B The motor losses during blocked rotor test are (A) Copper losses (C) Iron losses (B) Rotational losses (D) All of them Page 1 of 2 10 12 13 14 17 20