Download GTU (Gujarat Technological University) BE/BTech (Bachelor of Engineering / Bachelor of Technology) 2018 Winter 5th Sem Old 150902 Power System Analysis And Simulation Previous Question Paper
1
Seat No.: ________ Enrolment No.___________
GUJARAT TECHNOLOGICAL UNIVERSITY
BE - SEMESTER ?V (OLD) EXAMINATION ? WINTER 2018
Subject Code:150902 Date: 07/12/2018
Subject Name: Power System Analysis And Simulation
Time: 10:30 AM TO 01:00 PM Total Marks: 70
Instructions:
1. Attempt all questions.
2. Make suitable assumptions wherever necessary.
3. Figures to the right indicate full mark.
Q.1 (a) A 230-kV, 60 Hz three-phase transmission line is 80 km long. The per phase
series impedance and shunt admittance of the line are z = 0.05 + j0.45 ? per km
and y = j3.4 x 10
-6
siemens per km respectively. The line delivers 200 MVA at
0.8 lagging power factor at 220 kV. Using the nominal ? model, determine: (a)
The transmission line ABCD constants. b) Sending end voltage and current c)
Voltage regulation, d) Sending end power e) Transmission efficiency.
07
(b) A 20 MVA, 6.6 kV, 3-phase star-connected alternator having a reactance of 25%
is connected through a 10 MVA, 6.6 kV/33 kV transformer of 15% reactance to
a transmission line having a resistance and reactance per conductor per kilometer
of 0.25 ? and 1.2 ? respectively. 70 kilometers along the line, a short circuit
occurs between the three conductors. Find the current fed to the fault by the
alternator.
07
Q.2 (a) For a long transmission line, using rigorous solution method, obtain the
expressions relating sending end and receiving end voltages and currents and
expressions for A,B,C,D constants for long transmission Line.
07
(b) The line currents in three phase unbalanced system are IR=(12 + j6) A, IY=(12
? j12) A and IB=(-15 + j10) A. The phase sequence is RYB. Calculate the
positive, negative and zero sequence components of currents.
07
OR
(b) Draw an impedance diagram for the electric power system shown in Fig. 1,
showing all impedances in per unit on a 100-MVA base. Choose 20 kV as the
voltage base for generator G1.
Fig. 1
The three-phase power and line-line ratings are given below:
G 1: 90 MVA 20 kV X = 9%
T 1: 80 MVA 20/200 kV X = 16%
T 2: 80 MVA 200/20 kV X = 20%
G 2: 90 MVA 18 kV X = 9%
Line: 200 kV X = 120 ?
Load: 200 kV S = 48 MW + j64 Mvar
07
Q.3 (a) Draw and explain various transformer connections and their zero sequence
networks. In the diagrams of transformer connections, clearly show the current
paths through the transformer windings and through ground terminal wherever
applicable.
07
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1
Seat No.: ________ Enrolment No.___________
GUJARAT TECHNOLOGICAL UNIVERSITY
BE - SEMESTER ?V (OLD) EXAMINATION ? WINTER 2018
Subject Code:150902 Date: 07/12/2018
Subject Name: Power System Analysis And Simulation
Time: 10:30 AM TO 01:00 PM Total Marks: 70
Instructions:
1. Attempt all questions.
2. Make suitable assumptions wherever necessary.
3. Figures to the right indicate full mark.
Q.1 (a) A 230-kV, 60 Hz three-phase transmission line is 80 km long. The per phase
series impedance and shunt admittance of the line are z = 0.05 + j0.45 ? per km
and y = j3.4 x 10
-6
siemens per km respectively. The line delivers 200 MVA at
0.8 lagging power factor at 220 kV. Using the nominal ? model, determine: (a)
The transmission line ABCD constants. b) Sending end voltage and current c)
Voltage regulation, d) Sending end power e) Transmission efficiency.
07
(b) A 20 MVA, 6.6 kV, 3-phase star-connected alternator having a reactance of 25%
is connected through a 10 MVA, 6.6 kV/33 kV transformer of 15% reactance to
a transmission line having a resistance and reactance per conductor per kilometer
of 0.25 ? and 1.2 ? respectively. 70 kilometers along the line, a short circuit
occurs between the three conductors. Find the current fed to the fault by the
alternator.
07
Q.2 (a) For a long transmission line, using rigorous solution method, obtain the
expressions relating sending end and receiving end voltages and currents and
expressions for A,B,C,D constants for long transmission Line.
07
(b) The line currents in three phase unbalanced system are IR=(12 + j6) A, IY=(12
? j12) A and IB=(-15 + j10) A. The phase sequence is RYB. Calculate the
positive, negative and zero sequence components of currents.
07
OR
(b) Draw an impedance diagram for the electric power system shown in Fig. 1,
showing all impedances in per unit on a 100-MVA base. Choose 20 kV as the
voltage base for generator G1.
Fig. 1
The three-phase power and line-line ratings are given below:
G 1: 90 MVA 20 kV X = 9%
T 1: 80 MVA 20/200 kV X = 16%
T 2: 80 MVA 200/20 kV X = 20%
G 2: 90 MVA 18 kV X = 9%
Line: 200 kV X = 120 ?
Load: 200 kV S = 48 MW + j64 Mvar
07
Q.3 (a) Draw and explain various transformer connections and their zero sequence
networks. In the diagrams of transformer connections, clearly show the current
paths through the transformer windings and through ground terminal wherever
applicable.
07
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2
(b) With reference to Z-bus building algorithm of a power system network, explain
the type-2 and type-3 modifications with necessary equations.
07
OR
Q.3 (a) Explain sub-transient, transient and steady state reactances of synchronous
machine and draw the machine circuit models using them.
07
(b) A 3-phase transmission line, operating at 11 kV and having a resistance of 1.5 ?
and reactance of 6 ?, is connected to the generating station bus-bars through 5
MVA step-up transformer having a reactance of 5%. The bus-bars are supplied
by a 12 MVA alternator having 25% reactance. Take 12 MVA as base MVA.
Calculate the short circuit MVA fed to symmetrical fault between phases if it
occurs:
a) at the load end of transmission line;
b) at the high voltage terminals of the transformer.
07
Q.4 (a) Explain the operation principle of resonant grounding with suitable line diagram
and phasor diagram. Derive the expression for inductance of arc suppression coil
for resonant grounding.
07
(b) Write a short note on selection of circuit breakers. 07
OR
Q.4 (a) If value of impedance is given in ohm, derive necessary expression and hence
explain how new per unit impedance is obtained if there is a change of base kV
and base MVA. Discuss any four advantages of per unit system representation.
07
(b) Explain how the value of fault current can be computed for L-L-G fault occurring at
the terminals of an unloaded synchronous generator.
07
Q.5 (a) A transmission line, having a surge impedance of ?Z0? ohms, is terminated
through a resistance R. Derive the expression for co-efficient of reflection and
refraction for (i) Voltage waves (ii) Current waves.
07
(b) Explain: a) mechanism of corona formation, b) various characteristics of corona,
c) factors affecting corona.
07
OR
Q.5 (a) Derive the expression for attenuation of a travelling wave on transmission line. 07
(b) A 3-phase, 220 kV, 50 Hz transmission line consists of 1.4 cm radius conductors
spaced 2.5 m apart in equilateral triangular formation. If the temperature is 40 ?C
and atmospheric pressure is 76 cm, calculate the corona loss per km of the line.
Take conductor surface irregularity factor m0=0.85. and breakdown strength of
air at 76 cm of mercury and 25 ?C =21.2 kV/cm (r.m.s.)
07
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This post was last modified on 20 February 2020