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Subject Code: 2150908
GUJARAT TECHNOLOGICAL UNIVERSITY
BE - SEMESTER- V (New) EXAMINATION - WINTER 2019
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Subject Name: Electrical Power System — I
Time: 10:30 AM TO 01:00 PM
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Instructions:
- Attempt all questions.
- Make suitable assumptions wherever necessary.
- Figures to the right indicate full marks.
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Q.1 (a) Define electric power supply system. Draw a single line diagram of a typical a.c. power supply system. MARKS 03
(b) Represent per unit model of generator, transmission line and load. MARKS 04
(c) List out the advantages and disadvantages of d.c transmission over a.c transmission? MARKS 07
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Q.2 (a) What is Skin effect and proximity effect? MARKS 03
(b) Explain function of insulator and discuss pin type insulator. MARKS 04
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(c) Define the sag in overhead line. Derive the equation of sag in case of When supports are at equal and unequal level. Also find the sag during effect of wind and ice loading. MARKS 07
OR
(c) In a string of three units, the capacitance between each link pin to earth is 11 % of the capacitance of unit. Calculate the voltage across each unit and the string efficiency when the voltage across the string is 33 KV. MARKS 07
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Q.3 (a) Write shot note on bundle conductors. MARKS 03
(b) What do you mean by transposition of line? What is its effect on the performance of the line? MARKS 04
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(c) Derive an expression for the inductance per phase for a 3-phase overhead transmission line when conductors are unsymmetrically placed but the line is completely transposed. MARKS 07
OR
Q.3 (a) Derive an expression for electric potential at a charged single conductor. MARKS 03
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(b) Calculate the inductance of each conductor in a 3-phase, 3-wire system when the conductors are arranged in a horizontal plane with spacing such that D31 =4 m, D12 = D23 =2 m. The conductors are transposed and have a diameter of 2.5 cm. MARKS 04
(c) Derive the equation of Inductance of a single phase two wire system. MARKS 07
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Q.4 (a) Explain self GMD and mutual GMD. MARKS 03
(b) Derive the equation of Capacitance of a single phase line MARKS 04
(c) A d.c. distributor AB is fed at both ends. At feeding point A, the voltage is maintained at 230 V and at B, it is 235 V. The total length of the distributor is 200 meters and loads are tapped off as under: MARKS 07
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25 A at 50 m from A
50 A at 75 m from A
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30 A at 100 m from A
40 A at 150 m from A
The resistance per kilometer of one conductor is 0.3 ohm. Calculate the current in various sections of distributor and minimum voltage and the point at which it occurs.
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Date: 21/11/2019
Total Marks: 70
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Q.4 (a) Describe briefly different types of d.c. distributors. MARKS 04
(b) Give the difference between a.c and d.c distribution. MARKS 07
(c) Derive an expression for line to neutral capacitance for a 3-phase overhead transmission line when conductors are unsymmetrically placed but the line is completely transposed MARKS 03
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Q.5 (a) Give definition of per unit value. List out advantages of per unit system. MARKS 04
(b) Explain the PU representation of transformer. MARKS 07
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(c) What should be the desirable characteristics of insulating materials used in cables? Briefly describe some commonly used insulating materials for cables. MARKS 03
OR
Q.5 (a) Give the classification of cables. MARKS 04
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(b) A single —core cable has a conductor diameter of 1c.m. and insulation thickness of 0.4cm. If the specific resistance of insulation is 5x10'Q-cm, calculate the insulation resistance for a 2km length of cable. MARKS 07
(c) Explain the steady state model of synchronous machine with diagram MARKS 07
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