Download GTU BE/B.Tech 2019 Winter 6th Sem New 2160908 Electrical Power System ? Ii Question Paper

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GUJARAT TECHNOLOGICAL UNIVERSITY

BE - SEMESTER- VI (New) EXAMINATION - WINTER 2019

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Subject Code: 2160908

Subject Name: Electrical Power system — I1

Time: 02:30 AM TO 05:00 PM

Total Marks: 70

Date: 06/12/2019

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Instructions:

1. Attempt all questions.
2. Make suitable assumptions wherever necessary.
3. Figures to the right indicate full marks.

Q1

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1. Write voltage and current relationship of transmission line using A, B, C, D parameters. Write expression of A, B, C, D parameter in terms of Y and Z for medium transmission line and long transmission line. (MARKS 03)
2. Define positive, negative and zero sequence component. (MARKS 04)
3. Derive equation of voltage and current of long transmission line considering uniformly distributed parameters through the line. (MARKS 07)

Q2

1. Draw wave form of short circuit current of an alternator. Explain the subtransient, transient and steady state period. (MARKS 03)

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2. Explain Reactive power compensation of transmission line in brief. (MARKS 04)
3. A 3-phase 50 Hz, 120 km transmission line has following parameters. R=0.2O/km, L= 1.2 mH/km and c= 0.014pf/ km. Determine sending end voltage and efficiency. A line delivering power of 45 MW at 132KV and 0.85 power factor lagging. Use Nominal T method for calculation. (MARKS 07)

OR

1. The voltage across three phase unbalanced load are V_a=200<40°, V_b=320<90°, V_c =480 <340°.Determine symmetrical component of voltage. Phase sequence abc. (MARKS 07)

Q3

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1. Classify transmission line. (MARKS 03)
2. Draw and Explain zero sequence network of transformer for Y-Y, ?-?, ?-Y, Y-? connection with and without neutral grounded (MARKS 04)
3. Obtain expression of three phase power in terms of sequences component. (MARKS 07)

OR

1. Explain any two causes which are producing Transient on line. (MARKS 03)

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2. Explain zero sequence impedance and network for synchronous machine. (MARKS 04)
3. Write criteria for selection of circuit breaker. (MARKS 07)

Q4

1. Define surge impedance. Explain surge impedance loading of transmission line. (MARKS 03)
2. A 50 MVA, 11KV, 3-phase synchronous generator was subjected to 3-phase fault and line to line fault. A generator neutral is solidly grounded. Find out positive sequence and negative sequence reactance of synchronous generator if 3-phase fault is 1780A and line to line fault current is 2590A. (MARKS 04)

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3. Derive expression for fault current for single line to ground fault as an unloaded generator. (MARKS 07)

OR

1. Give model of synchronous machine with load under transient condition. (MARKS 03)
2. A’ Three phase power is transmitted by 132 kV overhead transmission line. The conductors are arranged in horizontal spacing. The conductor radius = 10 mm, Temperature = 22°C and pressure =73 cm of Hg. Surface factor m_v = 0.84. Obtain relative density and critical disruptive voltage. (MARKS 04)
3. Derive equation of restriking voltage across circuit breaker after removal of short circuit. (MARKS 07)

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Q.5

1. Write methods of reducing corona. (MARKS 03)
2. Discuss capacitance switching. (MARKS 04)
3. Consider the three bus system shown in fig.1 the generators are 100 MVA with a transient reactance of 10% each. Both the transformers are 100MVA with a leakage reactance of 5% The reactance of each line to a base of 100 MVA. 110KV is 10%. Find the value of fault current for a three phase solid short circuit on bus no: 3. Assume prefault voltages to be 1.0 p.u. and prefault currents to be zero. (MARKS 07)

OR

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1. Discuss the phenomena of wave reflection and wave refraction. (MARKS 03)
2. Describe formation of corona in H.V. transmission line. write merits and demerits of Corona (MARKS 04)
3. Introduce symmetrical components and state their application. Derive symmetrical components of a given set of three unbalanced line. (MARKS 07)

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