1. A T-T connection has higher ratio of utilization than a V-V connection only when ?
ans- non identical transformer are used .
2. For 3 to 3 phase converson , which polyphase connection would you select ?
ans- Delta / Inter connected star .
3. Five limb core construction of a transformer has advantage over three limb core construction that ?
ans- magnetic reluctance of the three phase can be balance .
4. Transformer winding are tapped in the middle because ?
ans- It eliminates axial force on the winding.
5. For large power transformer , it is preferred to use ?
ans- Tank with separated cooler.
6. In a transformer with close magnetic cooling between primary and secondary winding ?
ans- Regulation will be good .
7. For getting minimum weight of a transformer the weight of iron should be ?
ans- Equal to the weight of copper.
8. A constant current transformer should not have ?
ans- high value of resistance.
9. scott connection , th netural point divides the teaser winding in the ratio ?
ans- 1:2
10. Can a 50 HZ transformer be used for 25 HZ , if the input voltage is maintained constant at the rated value corresponding to 50 HZ ?
ans- No flux will be double which will drive the care to excessive saturation .
BRIEF NOTE ABOUT SEMICONDUCTOR DEVICES
11. The magnetic properties of silicon steel crystal are best ?
ans- Along the cube edges
12. The magnetic properties of CRGO silicon steel are excellent ?
ans- Along the direction of rolling .
13. For CRGO silicon steel metal overlap is prefered for the core yoke joints as ?
ans- It reduce magnetising current and also the core loss .
14. Major insulation of a transformer is the insulation between?
Ans- between the low voltage winding and the core & also between the low voltage & high voltage winding.
15. Minor insulation of a transformer is the insulation?
Ans- between the turns of the winding & also between the layer of the winding.
16. For off load tap changing, the best method is to use ?
Ans- Tap changers inside the tank operated by external selector switches.
17. For no laod tap changing ,the best method is to use ?
Ans- Tap changers outside the tank operated by selector switch.
18. In general, for all size of distribution transformer, it is preferable to use ?
Ans- Tubed tanks .
19. For small power transformer, it is preferable to use?
Ans- Tubed tank.
20. In the circuit model of transformer the copper loss can be represented as ?
Ans- Series resistance .
21. The permeability of the core of an ideal transformer must be
Ans- infinity .
22. Which of the following transformer secondary winding is connected to earth ?
Ans- Current transformer & potential transformer .
23. When the leakage flux in a transformer increase, it will decrease the ?
Ans- Secondary terminal voltage.
24. Air core transformer as compared to iron core transformer has ?
Ans- No magnetic loss.
25. The purpose of using CRGO steel for the core of transformer is to reduced ?
Ans- hystersis loss.
26. Which moderator is used in fast breeder reactor
Ans- No reactor is used.
27. When an induction motor runs at ratted load and speed the iron losses are ?
Ans- Negligible .
28. Large air gap in an induction motor results in ?
Ans- Reduced pulsation losses .
29. For smooth starting of three phase squrrel cage induction motor, the starting method preferred is ?
Ans- Auto transformer.
30. The high leakage impedance transformer are suitable for the application of ?
Ans- Arc welding
31. The constant voltage transformer are most commonly used in ?
Ans- Personal computers.
32. Whether the given auto transformer is step up or step down its VA rating is always?
Ans- Greater then the two winding transformer.
33. For stability & economic reasons we operate the transmission lines with power Angel in the range _______.
Ans- 30⁰ to 45⁰.
34. Ferranti effect on long overhead lines is experienced when it is_________.
Ans- Lightly loaded .
35. Stringing chat is used for ________.
Ans- Finding the sag in conductor.
36. On which factor good smoothing factor of a coil depends?
Ans- Inductivity of the coil.
37. The stator of morden alternator are wound for______ phase group.
Ans- 60⁰.
38. The rating of the synchronous machine is usually governed by its .
Ans- temp. Rise.
39. Laminated yoke in DC motor can reduce.
Ans- Iron loss
40. Pole of DC machine are often laminated to _______.
Ans- reduce pulsating loss.
41. Aluminium is not used as winding wire in DC machine armature as it.
Ans- Required large winding space.
42. The fifth harmonic component of phase emf for a three phase star connection is ?
Ans- 0
43. The working of the quartz crystal in the watch is based on the ?
Ans- Piezo- electric effect.
44. The base of electric iron is brightly polished mainly for ?
Ans- reduce heat loss by radiation.
45. Which is best used as a sound absorbing material in partition walls?
Ans- Glass wool
46. The most suitable unit for expressing nuclear radius is ?
Ans- Farmi
47. Ultrasonic waves are used for strring liquid solutions because they.
Ans- Can produce perfectly homogeneous solutions.
48. Optical fiber works on the principle of ?
Ans- total internal reflection
49. Acceptor impurities atom in a semi conductor result in new
Ans- Discrete energy level just above valency level.
50. In FET current flow is mainly due to ______ carrier.
Ans- Majority.
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