Tuesday, September 6, 2016
- Tuesday, September 06, 2016
- PunjabtechnicalUniversity ajay gour
- 3rd Semester Electrical(D), Electrical Engineering Materials Electrical(D) 3rd
- No comments
S.B. Roll No.______
ELECTRICAL ENGINEERING MATERIALS
Duration: 3 hrs.
Note: Attempt any five questions.
a. Give the atomic structure of any one of the semi conductor materials and explain how it differs form that of conducting and insulating materials.
b. A length of wire has a resistance of 14.5 ohms. Find the resistance of another wire of the same material, three times as long and twice a big in cross sectional area.
a. Explain why copper is used in the windings of electrical machines and in flexible wires oven through it is expensive.
b. Write down the names of the alloys composed of the following metals:
i. Iron –chromium-nickel
iv. Copper manganese-nickel
v. Copper zinc
c. State one application of each of the following in electrical field
a. State the properties of semi conducting materials.
b. How is insulation resistance affected by?
iv. Applied voltage
c. In case of insulating materials, define the following:
i. Volume resistivity
iii. Weather ability
a. Mention one electrical application of each of the following insulating material.
ii. Impregnated paper
iii. Class wool
b. State the purpose of Enameling, mention a few enamels with their applications
c. Which of the following are thermosetting or thermoplastic materials.
iii. Epoxy resins
a. State the difference between soft magnetic material and hard magnetic material.
b. How do the above two magnetic materials differ form each other?
c. State the properties of these two magnetic materials and applications.
a. Explain briefly the reasons for the following
i. Hearing element is not made of iron
ii. Conducting materials should have a low valve of temperature co-efficient of resistance
iii. Air is replaced by nitrogen as an insulating material in certain applications
iv. The windings of power transformer are immersed in oil.
v. Synthetic rubber is inferior to natural rubber in electrical properties.
b. Explain the phenomenon of hysteresis
a. What are bimetals ? where are they used?
b. State the advantages of cartridge fuse over Rewritable fuse.
c. State the applications of nitrogen , hydrogen of SF as insulating agent.
a. Why are conductors stranded?
b. Name the materials used in the manufacturing of transformer core. Give reasons for you answer.
c. What will be the effect on the rating of an apparatus if its insulation is by another of higher temperature class?
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