1. A 100V/10V,50VA Transformer is converted to 100V/110V Autotransformer, the rating of the Autotransformer will be
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2. The efficiency at a 100KVA Transformer is 0.98 at full as well as half load.For this transformer at Full load the copper loss
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3. In Autotransformer,the number of turn in primary winding is 210 and in secondary winding is 140.If the input current is 60A,the current in output and in common winding are respectively
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4. A transformer has core loss of 64W and copper loss of 144W,When it is carrying 20% overload current.The load at which this transformer will operate at the maximum efficiency_________
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5.Leakage flux in a transformer occur because
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6. The short cicuit test in a transformer is used to
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7.which of the following transformer is smallest
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8. Stepped cores are used in transformer in order to reduce
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9. The heat generated in the transformer is dissipated mainly by
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10. The No-Load current in a transformer is
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11.What does CRGO stand for?
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12. What is the main advantage of using CRGO in transformer cores?
13.Which process is used to manufacture CRGO?
14. What is the thickness range of CRGO used in transformer cores?
15.What is the main disadvantage of using CRGO in transformer cores?
16.What is the composition of CRGO?
17.What is the purpose of the grain orientation in CRGO?
18.What is the maximum flux density that can be achieved with CRGO?
19.What is the typical application of CRGO besides transformer cores?
20.What is the difference between CRGO and CRNGO?
Explain:-
CRGO stands for Cold Rolled Grain Oriented electrical steel. It is a type of electrical steel that is specially processed to have a specific grain orientation. The purpose of this grain orientation is to reduce the core loss in transformers and electrical motors.
The composition of CRGO includes iron, silicon, and carbon, with silicon being the most important component. The typical silicon content in CRGO is around 3%. The carbon content is kept low to prevent the formation of carbides that can reduce the magnetic properties of the material.
The maximum flux density that can be achieved with CRGO is around 1.9 tesla. This is due to the saturation point of the material, beyond which the magnetic properties start to degrade.
CRGO is used in the manufacturing of transformer cores, especially those used in high-efficiency transformers. It is also used in the production of electrical motors, especially those used in high-performance applications.
The difference between CRGO and CRNGO (Cold Rolled Non-Grain Oriented) is that CRNGO does not have a specific grain orientation. This makes it less efficient than CRGO in terms of reducing core loss. However, it is cheaper and easier to manufacture than CRGO, making it suitable for applications where high efficiency is not critical.
In summary, CRGO is an important material used in the manufacturing of transformer cores and electrical motors. Its composition, purpose of grain orientation, maximum flux density, and typical applications are important to understand for exams related to electrical engineering, materials science, and manufacturing processes.
21.Which organization sets the standards for CRGO used in transformer cores?
22.What is the typical loss factor of CRGO used for transformer cores?
23.What is the typical stacking factor of CRGO used for transformer cores?
24.What is the main advantage of using CRGO in transformers?
Explain:-
Advantages:
1. Low losses: CRGO has low core loss and hysteresis loss, making it highly efficient in energy conversion.
2. High magnetic permeability: CRGO has high magnetic permeability, which allows it to store and transfer energy efficiently.
3. High saturation flux density: CRGO can withstand high magnetic fields without saturating, which makes it ideal for use in transformers.
4. Good dimensional stability: CRGO maintains its shape and size even under high temperatures and magnetic fields, ensuring consistent performance over time.
5. Cost-effective: CRGO is a cost-effective material for transformer cores compared to other materials like amorphous metal.
Disadvantages:
1. Brittle: CRGO is a brittle material that can crack or break easily if not handled carefully during manufacturing or installation.
2. Limited availability: CRGO is not readily available in all regions, which can increase shipping costs and lead times.
3. Susceptible to corrosion: CRGO is prone to corrosion if exposed to moisture or acidic environments, which can affect its performance over time.
4. Limited temperature range: CRGO has a limited temperature range, and exposure to high temperatures can cause it to lose its magnetic properties.
5. Limited flexibility: CRGO cannot be easily shaped or bent, which limits its use in certain applications.
25.The All day Efficiency of a DT will be high with low
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The all day efficiency of a distribution transformer refers to the ratio of the energy output of the transformer to the energy input over a 24-hour period. It is a measure of the transformer's efficiency in converting electrical energy from the primary side to the secondary side.
Advantages:
1. Energy savings: A transformer with high all day efficiency can save energy and reduce electricity costs over time.
2. Reduced carbon footprint: Improved efficiency also leads to reduced greenhouse gas emissions, contributing to a cleaner environment.
3. Longer lifespan: Efficient transformers generate less heat and operate at lower temperatures, which can extend their lifespan.
4. Improved voltage regulation: Efficient transformers maintain more stable output voltages, which can improve the quality of power delivered to end-users.
5. Compliance with regulations: Many countries have regulations that require distribution transformers to meet minimum all day efficiency standards.
Disadvantages:
1. Higher initial cost: Transformers with higher all day efficiency may have a higher initial cost compared to less efficient models.
2. Maintenance requirements: Efficient transformers may require more frequent maintenance to ensure they continue to operate at peak performance.
3. Limited availability: High-efficiency transformers may not be readily available in all regions, which can increase shipping costs and lead times.
4. Limited flexibility: Some applications may require transformers with specific efficiency ratings that are not readily available, limiting flexibility in design and installation.
5. Compatibility issues: High-efficiency transformers may not be compatible with certain types of loads or electrical systems, requiring additional equipment or modifications.
26.The advantage of putting tapping at the phase ends of a transformer is_______________
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27. Tapping of Transformer are provided
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28. What is the effect of using a transformer with a higher flux density on its efficiency?
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29. What is the effect of increasing the temperature on flux density in a transformer core?
30.The use of higher flux density in the transformer design
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31. Which of the following is the characteristic of amorphous core transformers ?
31*. No-load current of a transformer has
32. Spacers are provided between adjacent coils
33. Greater the secondary leakage flux
34. The purpose of providing iron core in a step-up transformer is
35. The power transformer is a constant
36. Two transformers operating in parallel will share the load depending upon their
37. If R2 is the resistance of secondary winding of the transformer and K is the transformation ratio then the equivalent secondary resistance referred to primary will be
38. What will happen if the transformers working in parallel are not connectedwith regard to polarity ?
39. If the percentage impedances of the two transformers working in parallel aredifferent, then
40. In a transformer the tappings are generally provided on
41. The use of higher flux density in the transformer design
42. The chemical used in breather for transformer should have the quality of
43. The chemical used in breather is
44. The transformer ratings are usually expressed in terms of
45. The noise resulting from vibrations of laminations set by magnetic forces, istermed as
46. Hysteresis loss in a transformer varies as CBmax = maximum flux density)
47. Material used for construction of transformer core is usually
48. The thickness of laminations used in a transformer is usually
49. The function of conservator in a transformer is
50. The highest voltage for transmitting electrical power in India is
51. In a transformer the resistance between its primary and secondary is
52. A transformer oil must be free from
53. A Buchholz relay can be installed on
54. Gas is usually not liberated due to dissociation of transformer oil unless theoil temperature exceeds
55. The main reason for generation of harmonics in a transformer couldbe
56. Distribution transformers are generally designed for maximum efficiency around
57. Which of the following property is not necessarily desirable in the material for transformer core ?
58. Star/star transformers work satisfactorily when
59. Delta/star transformer works satisfactorily when
60. Buchholz’s relay gives warning and protection against
61. The magnetising current of a transformer is usually small because it has
62. Which of the following does not change in an ordinary transformer ?
63. The leakage flux in a transformer depends upon
64. The path of the magnetic flux in transformer should have
65. Noise level test in a transformer is a
66. Which of the following is not a routine test on transformers ?
67. A transformer can have zero voltage regulation at
68. Helical coils can be used on
69. The core used in high frequency transformer is usually
70. The value of flux involved in the e.m.f. equation of a transformer is
71. Harmonics in transformer result in
72. The full-load copper loss of a trans¬former is 1600 W. At half-load, thecopperloss will be
73. Silicon steel used in laminations mainly reduces
74. Which winding of the transformer has less cross-sectional area ?
75. Power transformers are generally designed to have maximumefficiencyaround
76. Which of the following is the main advantage of an auto-transformer overatwo winding transformer ?
77. During short circuit test iron losses are negligible because
78. Two transformers are connected in parallel. These transformers do not have equal percentage impedance. This is likely to result in
79. The changes in volume of transformer cooling oil due to variation of atmospheric temperature during day and night is taken care of by which part of transformer
80. An ideal transformer is one which has