JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD

JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech III Year II Semester DESIGN ESTIMATION AND COSTING OF ELECTRICAL SYSTEMS Previous Question Paper (August/September - 2024 - R16)

B.Tech | III Year II Semester | III-II | R16 | August/September - 2024

Answer PaperPaper Code: 136EWMaximum Marks: 75Time: 3 Hours

Note: Part A is compulsory (25 marks). Answer all questions. Part B (50 marks): Answer any one question from each unit (10 marks each).

Part A

1.a

What is the necessity of earthing in electrical systems?

2 marks

Answer

  • Personnel Safety: The primary necessity of earthing is to protect human life from the danger of electric shock. By connecting the non-current-carrying metallic parts of electrical equipment to the general mass of the earth, any insulation failure that causes the frame to become live results in a low-resistance path for the fault current, triggering protective devices like fuses or circuit breakers to isolate the circuit immediately.
  • Voltage Stabilization: Earthing ensures that the potential of the current-carrying conductors remains fixed with respect to the earth, preventing dangerous voltage surges caused by lightning strikes, line surges, or accidental contact with higher voltage lines.
  • Equipment Protection: It provides a stable reference potential for sensitive electronic equipment and prevents the accumulation of static charges, which could otherwise damage insulation or cause interference in communication systems.
  • System Reliability: Proper earthing facilitates the operation of protective relays and fault-clearing equipment, ensuring that ground faults are detected and cleared rapidly, thereby minimizing damage to electrical infrastructure.
1.b

What is the role of circuit breaker in electrical system?

3 marks

Answer

A circuit breaker is an essential automatic electrical switching device designed to protect an electrical circuit from damage caused by excess current resulting from an overload or a short circuit. Its primary roles in an electrical system include:
  • Fault Interruption: It acts as a protective device that detects abnormal current conditions (such as faults) and automatically interrupts the power supply to prevent damage to equipment, cables, and infrastructure.
  • Manual Switching: It serves as a manual disconnect switch, allowing operators to isolate specific sections of a power system for maintenance, repair, or inspection purposes.
  • Arc Extinction: During the interruption of high-magnitude fault currents, an electric arc is formed between the contacts. The circuit breaker is specifically engineered to extinguish this arc rapidly using various media such as air, oil, vacuum, or sulfur hexafluoride (SF6) gas, ensuring the safety of the system.
  • System Reliability: By isolating only the faulty section of a network while allowing healthy sections to remain energized, circuit breakers ensure the continuity and reliability of the overall electrical distribution system.
Unlike a fuse, which is a single-use device that must be replaced after operation, a circuit breaker can be reset (either manually or remotely) once the fault has been cleared, making it more efficient for modern electrical installations.
1.c

How the fuse rating and starter are decided in factory unit.

2 marks

Answer

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1.d

Explain the differences between shop and street lighting.

3 marks

Answer

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1.e

What is meant by sag in transmission lines?

2 marks

Answer

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1.f

What is potential gradient in underground cables?

3 marks

Answer

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1.g

What is the functions of busbar in a substation?

2 marks

Answer

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1.h

What are the advantages of Indoor substations?

3 marks

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1.i

What is the normal life of a fluorescent lamp?

2 marks

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1.j

What will be the utilization factor for an indirect lighting scheme?

3 marks

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Part B

210 marks
a
State the necessity of testing of electrical installation before its commissioning.
5 marks

Answer

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b
What are various types of faults that occurs in distributed system? How electric system is protected from short circuits?
5 marks

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OR
310 marks
a
Explain about various types of loads in power system.
5 marks

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b
Write about the guide lines followed for Installation of fitting.
5 marks

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410 marks
a
Explain about mounting arrangements and positioning of switch boards and distribution boards main switch in commercial installation.
4 marks

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b
A reading room 50m × 15m × 6m requires an illumination of 40meter-candle on the reading table. Assuming a space height ratio of 1.2 calculate (i) the number of lamps required (ii) C.P of each. Assuming the utilization factor as 0.4, depreciations factor as 0.75 efficiency of each lamp as 0.75watts per candle power and the height of lamps above the reading table as 4m. Draw a sketch of arrangement of lamps.
6 marks

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OR
510 marks
a
Explain the procedure to perform insulation resistance test between conductors.
4 marks

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b
An illumination of 300lux is to provide in a class room of 20m × 10m with 40W fluorescent lamps. Determine the number and layout in the lighting installations. Assume data not given.
6 marks

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610 marks
a
What are the factors that make to choose power distribution through underground cables?
4 marks

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b
Discuss in detail about the material required for the laying of overhead transmission lines.
6 marks

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OR
710 marks
a
What are different types of underground cables used in distribution system? Explain them.
6 marks

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b
List the different types of pole structures used in distribution lines.
4 marks

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810 marks
a
State any eight electrical equipment required in 11 kV HT substation.
6 marks

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b
What are the advantages and disadvantages of pole mounted type substations? Explain.
4 marks

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OR
910 marks
a
What is an outdoor substation? What are its features?
5 marks

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b
List the materials required for overhead service connection?
5 marks

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1010 marks
a
State and explain laws of illumination.
5 marks

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b
What are the main types of practical lightning schemes?
5 marks

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OR
1110 marks
a
Compare CFL with OCFL lamp.
5 marks

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b
What are various types of light sources? Explain.
5 marks

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About this paper

This page contains the solved question paper with answers of DESIGN ESTIMATION AND COSTING OF ELECTRICAL SYSTEMS from JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD for B.Tech CE III Year II Semester III-II, August/September - 2024, R16.

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