electrical machines transformers induction motors synchronous machines dc machines characteristics starting control losses efficiency - One Line Questions

1. A three-phase transformer can be connected in Delta-Delta configuration. What is the phase shift introduced between primary and secondary line voltages? — 0 degrees
2. What is the slip of an induction motor when it is running at synchronous speed? — 0
3. A synchronous motor operates at: — A speed equal to synchronous speed
4. The maximum torque of an induction motor occurs at a slip value that is: —
5. The principle of operation of a transformer is based on: — Faraday's law of electromagnetic induction
6. The V-curves of a synchronous machine represent the variation of: — Armature current with field current
7. The torque produced by a DC motor is directly proportional to: — Armature current and field flux
8. Which type of transformer is commonly used for stepping down voltage in power distribution systems? — Step-down transformer
9. The efficiency of a transformer is generally highest when: — Copper losses are equal to iron losses
10. In a transformer, the ratio of output voltage to input voltage is called: — Transformation ratio
11. Which of the following is a method of starting a large three-phase induction motor to reduce starting current? — All of the above
12. What is the main cause of hysteresis loss in a transformer core? — Rapid reversal of magnetization in the core material
13. A DC motor converts: — Electrical energy into mechanical energy
14. In a DC generator, the induced EMF is proportional to: — Field flux and speed
15. Eddy current losses in a transformer core can be reduced by: — Laminating the core
16. The losses that vary with the square of the load current in a transformer are called: — Copper losses
17. Which type of transformer has a single winding that serves as both primary and secondary? — Autotransformer
18. What is the power factor of a synchronous motor when over-excited? — Leading
19. The maximum efficiency of a transformer occurs when: — Iron losses equal copper losses
20. What is the primary disadvantage of a wound rotor induction motor compared to a squirrel cage motor? — More complex construction and higher maintenance
21. Which test is performed on a transformer to determine its copper losses? — Short-circuit test
22. A synchronous motor can be used for: — Power factor correction
23. In an ideal transformer, which of the following is assumed to be zero? — Core losses
24. A synchronous motor is inherently: — Not self-starting
25. A cumulative compound DC motor has: — Series field assisting the shunt field
26. Which type of DC motor has a speed that increases significantly with the decrease in load? — Series motor
27. Which DC motor has the poorest speed regulation? — Series motor
28. The difference between the synchronous speed and the actual rotor speed of an induction motor is called: — Slip
29. What is the starting torque of a three-phase induction motor proportional to? — Square of the supply voltage
30. The field winding of a synchronous motor is located on the: — Rotor
31. Which component is responsible for maintaining the direction of torque in a DC motor? — Commutator and brushes
32. Hunting in a synchronous motor is caused by: — All of the above
33. In an induction motor, the rotor's magnetic field rotates at: — Synchronous speed
34. The back EMF in a DC motor opposes: — The applied voltage
35. What is the synchronous speed of an induction motor? — The speed of the rotating magnetic field
36. What is the role of a commutator in a DC machine? — To reverse the direction of current in the armature winding
37. What is the purpose of the conservator in a power transformer? — To provide space for oil expansion and contraction
38. What is the purpose of damper windings in a synchronous machine? — To provide starting torque and prevent hunting
39. What is the primary function of a transformer? — To change the voltage level of AC power
40. What is the function of the interpoles in a DC machine? — To reduce the armature reaction and improve commutation
41. What is the purpose of a starter in a DC motor? — To limit the starting current
42. What is the main purpose of the oil in a power transformer? — To act as a coolant and insulating medium
43. A DC shunt motor is generally preferred for: — Applications requiring constant speed
44. When a synchronous motor is operated at its rated load and unity power factor, its excitation is: — Normally excited
45. The efficiency of a DC machine is maximum when: — Variable losses are equal to constant losses
46. Which method is commonly used to control the speed of a three-phase induction motor? — All of the above
47. The ratio of the number of turns in the secondary winding to the number of turns in the primary winding of a transformer is called the: — Turns ratio
48. What is the unit of apparent power in an AC circuit? — Volt-Amperes (VA)
49. What is the unit of magnetic flux density? — Tesla (T)
50. In a squirrel cage induction motor, the rotor bars are: — Short-circuited by end rings
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