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Paper Id: 2 0 3 1 Roll No:
B TECH
(SEM V) THEORY EXAMINATION 2017-18
ELEMENTS OF POWER SYSTEM
Time: 3 Hours Total Marks: 100
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Notes: Attempt all Sections. Assume any missing data.
SECTION -A (2x10=20)
1. Attempt all question in brief:
- a) How does isolator differ from circuit breaker?
- b) What is single line diagram of power system?
- c) What are the components of transmission line?
- d) What is transposition of transmission line?
- e) Write advantages of bundled conductor.
- f) Define the term Corona.
- g) What is the failure of insulators?
- h) Define Sag in transmission line.
- i) What is general construction of cable?
- j) What are the advantages of neutral grounding?
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SECTION -B
2. Attempt any three parts of the following: (10x3=30)
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- (a) Find the ratio of volume of copper required to transmit a given power over a given distance by overhead system using (i) DC two wire system (ii) 3-phase 4-wire system.
- (b) Derive A, B, C and D parameters for nominal p model of a medium transmission line and draw its Phasor diagram.
- (c) Explain the phenomenon of corona formation and factors affecting, reducing corona. What is visual critical voltage?
- (d) Why do the vibrations get generated in conductors? How are they damped? Explain effect of wind and ice loading on the mechanical design of a line.
- (e) What are advantages of HV DC transmission? Discuss various types of HVDC links.
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SECTION -C (10x1=10)
3. Attempt any one parts of the following:
- a) State and explain Kelvin's law for economic size of conductor. Discuss limitations. Show how Skin effect increases effective resistance of the conductor.
- b) Determine the best current density in amperes/mm² for a three phase overhead line. The line is in use for 3600 hours per year and if the conductor costs Rs. 3.0 / kg. It has a specific resistance of 1.73 x 10-8 O-m and weighs 6200 kg / m³.cost of energy is 12 paise / unit. Interest and depreciation is 10 % of conductor cost.
4. Attempt any one parts of the following: (10x1=10)
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- a) Derive an expression for the capacitance of a single phase overhead transmission line. What do you mean by self G.M.D. and mutual G.M.D.
- b) A two conductor, single phase line operates at 60 Hz. The diameter of each conductor is 5 cm and is spaced 3 m apart: calculate (i) the capacitance of each conductor to neutral per Km (ii) line to line capacitance (iii) capacitive susceptance to neutral per km.
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5. Attempt any one parts of the following: (10x1=10)
- a) Describe pin type, suspension type, and strain type insulators with net sketch.
- b) Explain the methods of equalizing the potential across the string insulator. And define string efficiency.
6. Attempt any one parts of the following: (10x1=10)
- a) Explain catenary method for the calculation of sag and tension in transmission line. An overhead line has a span of 200 metres, the line conductor weighs 0.7 kg per meter. Calculate the maximum sag if allowable tension in the line is 1,400 kg. Prove formula used.
- b) What is grading of cable? Why is it necessary? Explain Capacitance grading with suitable circuit Diagram.
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7. Attempt any one parts of the following: (10x1=10)
- a) What are earthing and neutral grounding? Discuss different methods of neutral grounding with net sketch. Also give advantages.
- b) Describe the various conductor configurations and choice of voltage, number of circuits for EHV Transmission lines. Make Economic comparison of EHV-AC & HVDC system.
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