Seat No.: ________ Enrolment No.___________ Q.

3 (a) Explain Ferranti effect 03

(b) Draw and discuss the operating chart of a synchronous generator 04
GUJARAT TECHNOLOGICAL UNIVERSITY (c) Show how Zbus matrix gets modified when branch Zb is added 07
BE – SEMESTER- V EXAMINATION-SUMMER 2023 from new bus to old bus (type-2 modification), and when Zb
connects old bus to reference bus (type-3 modification)
Subject Code: 3150911 Date: 03/07/2023
Subject Name: Power System- II Q.4 (a) Draw the zero sequence reactance diagram of transformers having 03
Time: 02:30 PM TO 05:00 PM Total Marks: 70 the following connections (i) delta-delta (ii) star-delta with star side
Instructions: grounded
1. Attempt all questions. (b) A 3-φ short transmission line has a resistance of 5Ω per phase and 04
2. Make suitable assumptions wherever necessary. inductive reactance of 15Ω per phase. If the sending end and
3. Figures to the right indicate full marks. receiving end voltage are 140 kV and 132 kV respectively, find the
4. Simple and non-programmable scientific calculators are allowed.
horizontal and vertical co-ordinate of the receiving end power
MARKS circle diagram (i.e. centre of the circle) in MW and MVAR
(c) Derive the expression for fault current for a double line to ground 07
Q.1 (a) How capacitance present between the line and ground is taken into 03 fault at the generator terminals. Also discuss how sequence
account while modelling medium length transmission line? networks are connected for L-L-G fault.
(b) An overhead 3-φ short transmission line delivers 5000 kW at 22 04 OR
kV at 0.8 pf lagging. The resistance and reactance of each Q.4 (a) Explain corona phenomena in transmission lines 03
conductor is 4Ω and 6Ω respectively. Determine (i) the sending end (b) Determine the disruptive critical voltage and corona loss for a 3- 04
voltage (ii) percentage regulation phase line operating at 110 kV which has conductor of 1.25 cm
(c) Prove that per-unit impedance of a transformer is same whether it 07 diameter arranged in a 3.05 meter delta. Assume air density factor
is computed from primary or secondary side of 1.07 and dielectric strength of the air to be 21 kV/cm
(c) A 25 MVA, 11 kV generator has X’’d = 0.2 pu. Its negative and 07
Q.2 (a) Distinguish between symmetrical and unsymmetrical faults giving 03 zero sequence reactances are 0.3 and 0.1 pu respectively. The
appropriate examples neutral of the generator is solidly grounded. Determine the
(b) In a 3-φ, 4-wire system, the currents in phase A,B and C under 04 subtransient current in the generator and the line to line voltages
abnormal loading conditions are given by Ia = 100/300 A, Ib = for subtransient conditions when an L-G fault occurs at the
50/3000 A, Ic = 30/1800 A. Calculate the positive and zero generator terminals. Assume that generator is operating on no-load
sequence currents Ia1, Ia0 and return current in the neutral wire. before the fault occurs
(c) Using rigorous solution method, derive the expression for ABCD 07
constants of a long transmission line in terms of hyperbolic sine Q.5 (a) A wave travels over a line and enters the cable. The surge 03
and cosine terms impedance of overhead line and cable are 400Ω and 40Ω. Find the
OR value of refracted voltage wave as percentage of incident voltage
(c) Prove that travelling wave on a transmission line travels at the 07 wave
speed of light. What would be the velocity of a surge, travelling in (b) Explain in brief the different methods of voltage control 04
cable having relative permittivity of 5? employed in power systems
(c) Explain the phenomena of arcing grounds in an isolated neutral 07
Q.3 (a) Show that symmetrical component transformation is power 03 systems. Discuss why it can cause severe overvoltages in a power
invariant system.
(b) Discuss the criteria for selection of circuit breakers 04 OR
(c) A 100 MVA, 33 kV, 3-φ generator has a reactance of 15%. The 07 Q.5 (a) A 500 kV, 2μS rectangular surge on a line having a surge 03
generator is connected to the motors through a transformer and impedance of 350Ω approaches a station at which the concentrated
transmission line as shown in figure 1. Motors have rated inputs of earth capacitance is 3000 pF. Determine the maximum value
40 MVA, 30 MVA and 20 MVA with 20% reactance each. Draw transmitted wave
the per-unit reactance diagram. Assume a base of 100 MVA and 33 (b) Derive the expression for refracted voltage wave due to a surge 04
kV in generator circuit. travelling at T-junction
(c) Discuss the different types of lightning strokes and their harmful 07
effects on power system

*************
Figure-1
OR
1 2
Seat No.: ________ Enrolment No.___________ (b) Explain reflection and refraction at a T-junction for travelling wave with 04
necessary equation.
GUJARAT TECHNOLOGICAL UNIVERSITY (c) Derive the equation for attenuation of travelling waves 07
BE - SEMESTER–V(NEW) EXAMINATION – SUMMER 2022
*************
Subject Code:3150911 Date:09/06/2022
Subject Name:Power System- II
Time:02:30 PM TO 05:00 PM Total Marks: 70
Instructions:
1. Attempt all questions.
2. Make suitable assumptions wherever necessary.
3. Figures to the right indicate full marks.
4. Simple and non-programmable scientific calculators are allowed.

Q.1 (a) What is p.u. system? Give the advantages of p.u. system 03
(b) Explain power in single phase AC circuits briefly 04
(c) Explain rigorous solution of long transmission line 07

Q.2 (a) Write a short note on Ferranti effect. 03

(b) Show that symmetrical component transformation is power invariant. 04
(c) Explain working of a synchronous generator connected to infinite bus. Draw 07
equivalent circuit and phasor diagram.
OR
(c) Derive equations of power flow through a transmission line. 07

Q.3 (a) Explain classification of transmission lines. Define voltage regulation and 03
efficiency of a transmission line.
(b) What is receiving end power circle diagram? Write down steps to draw it. 04
(c) Explain phase shift in star-delta transformer with phasor diagram. 07
OR
Q.3 (a) Explain ABCD constant for medium transmission line. 03
(b) Explain salient pole synchronous generator with power angle curve in short. 04
(c) Discuss transients on a transmission line in case of a symmetrical fault. 07

Q.4 (a) Differentiate symmetrical and unsymmetrical faults. List various 03

unsymmetrical faults.
(b) Explain analysis of a line to line fault. 04
(c) Explain types of lightning strokes. 07
OR
Q.4 (a) What is corona? Write formula of Disruptive critical voltage and briefly 03
describe each variable in the formula.
(b) Write a short note on selection of circuit breaker. 04
(c) Derive all components of V and I for double line to ground fault on an 07
unloaded generator with sequence network. (consider 3-phase star connected
generator with ground neutral)

Q.5 (a) Write a short note on radio interference. 03

(b) Explain overvoltage due to arcing ground with necessary vector diagram. 04
(c) Write a note on following: 07
(1) Lightning Arresters (2) Surge absorber
OR
Q.5 (a) Write a brief note on capacitance switching. 03

1 2
Seat No.: ________ Enrolment No.___________

GUJARAT TECHNOLOGICAL UNIVERSITY

BE - SEMESTER–V (NEW) EXAMINATION – WINTER 2023
Subject Code:3150911 Date:20-12-2023
Subject Name: Power System- II
Time:10:30 AM TO 01:00 PM Total Marks:70
Instructions: Fig. 1
1. Attempt all questions. All reactance are in p.u. on generator base.
2. Make suitable assumptions wherever necessary. OR
3. Figures to the right indicate full marks. Q.4 (a) How can effect of load current can be taken in to account in fault 03
4. Simple and non-programmable scientific calculators are allowed. calculation?
(b) Write a short note on selection of circuit breaker. 04
MARKS (c) Using appropriate interconnection of sequence networks, derive the 07
Q.1 (a) What is BIL? 03 equation for a line to line fault in a power system with fault impedance of
(b) What is arcing ground phenomenon? 04 Zf.
(c) Discuss the phenomenon of wave reflection and refraction. Derive 07
expression for reflection and refraction. Q.5 (a) Give classification of faults and discuss their nature of occurrence. 03
(b) Derive necessary equations to convert (a) phase quantities into 04
Q.2 (a) What is meant by corona? Why does it occur? 03 symmetrical components (b) symmetrical components in to phase
(b) What is difference between visual critical voltage and disruptive critical 04 quantity.
voltage? (c) Discuss the significance of zero sequence circuit. Why should Zn appear 07
(c) Discuss in detail factors and conditions affecting corona loss. 07 as 3Zn in zero sequence equivalent circuit?
OR OR
Q.2 (c) A 3 phase overhead line has conductors of 30 mm diameter and arranged in the 07 Q.5 (a) What are the symmetrical components and its need? 03
form of equilateral triangle. Assume fair weather conditions, air density factor of (b) Draw zero sequence network of a three phase transformer with 04
0.95 and irregular factor of 0.95. Find minimum spacing between conductors if (1) Star-Star connection with both neutrals grounded
disruptive critical voltage is not to exceed 230 kV between lines. Breakdown (2) Star delta connection with star side neutral grounded
strength of air is 30 kV/CM
(c) Find the symmetrical components for the given three phase currents 07
Q.3 (a) Differentiate between nominal T and equivalent T circuits. 03
(b) Why equivalent π circuit of a long line is preferred to the equivalent T 04
circuit?
(c) Draw the phasor diagrams of nominal π circuit and nominal T circuit of a 07
transmission line. Derive expressions for sending end voltage and current **********
in each case.
OR
Q.3 (a) What is Ferranti effect? 03
(b) Why representation of a line by lumped parameters gives inaccurate 04
results for long lines?
(c) Starting from first principles deduce expression for ABCD constants for a 07
long line in terms of its parameters. Define propagation constant and
characteristic impedance.

Q.4 (a) What is the difference between symmetrical and unsymmetrical faults? 03
(b) List the steps to calculations fault calculations. 04
(c) Calculate the sub transient fault current in each phase for a dead short 07
circuit on one phase to ground at bus Q for the system shown in Fig. 1

1 2
Seat No.: ________ Enrolment No.___________ Q.7 (a) Explain the phenomena of corona 03
(b) Explain overvoltage due to arcing ground with necessary vector 04
GUJARAT TECHNOLOGICAL UNIVERSITY diagram.
BE- SEMESTER–V (NEW) EXAMINATION – WINTER 2020 (c) Derive the equation for attenuation of travelling waves 07
Subject Code:3150911 Date:29/01/2021
Q.8 (a) Write a brief note on capacitance switching. 03
Subject Name:Power System- II (b) Give reasons for following: The disruptive critical voltage is less than 04
Time:10:30 AM TO 12:30 PM Total Marks: 56 visual critical voltage.
Instructions: (c) Explain travelling waves of a transmission line when the receiving 07
1. Attempt any FOUR questions out of EIGHT questions. end is short circuited.
2. Make suitable assumptions wherever necessary.
3. Figures to the right indicate full marks. *************
MARKS
Q.1 (a) Explain Types of Transmission Line. 03
(b) Write a short note on 04
(I) Ferranti effect
(II) Tuned power lines
(c) Using Rigorous, Derive expressions for sending end voltage current 07
for long transmission line.

Q.2 (a) What is p.u. system? Give the advantages of p.u. system 03
(b) Explain power in single phase AC circuits briefly 04
(c) A synchronous generator is rated 645 MVA, 24 KV, 0.9 pf lagging. It 07
has a synchronous reactance 1.2 Ω. The generator is feeding full load
at 0.9 pf lagging at rated voltage. Calculate:
(a) Excitation emf (Ef) and power angle δ
(b) Reactive power drawn by the load
Carry out calculations in pu form and convert the result to actual
values.
Q.3 (a) Give classification of faults. What is difference between steady state 03
reactance Xd, transient reactance Xd’ and sub-transient reactance
Xd’’?
(b) What is receiving end power circle diagram? Write down steps to 04
draw it.
(c) Explain factors deciding selection of circuit breaker. 07

Q.4 (a) Explain the performance of loaded Synchronous Machine. 03

(b) Why does a generator produce only positive sequence voltage? 04
(c) A 50 Hz transmission line 300 km long has a total series impedance 07
of 40 + j125 ohms and a total shunt admittance of 10-3 mho. The
receiving end load is 50MW at 220 KV with 0.8 lagging pf. Find the
sending end voltage, current, power and power factor using nominal –
π method.
Q.5 (a) What are symmetrical components and its need? 03
(b) Write and explain symmetrical component transformation 04
(c) Using appropriate interconnection of sequence networks, derive the 07
equation for a line to line fault in a power system with fault
impedance of Zf.

Q.6 (a) Differentiate symmetrical and unsymmetrical faults. List various 03

unsymmetrical faults.
(b) Write equation of phase voltage in terms of symmetrical components 04
(c) Explain sequence impedances and networks of synchronous machine. 07

1 2
 Seat No.: ________ Enrolment No.___________

GUJARAT TECHNOLOGICAL UNIVERSITY

BE - SEMESTER–V (NEW) EXAMINATION – SUMMER 2024
Subject Code: 3150911 Date:31-05-2024
Subject Name: Power System- II
Time:02:30 PM TO 05:00 PM Total Marks:70
Instructions:
1. Attempt all questions.
Fig. 1
2. Make suitable assumptions wherever necessary.
3. Figures to the right indicate full marks.
4. Simple and non-programmable scientific calculators are allowed. OR
Q.3 (a) Why are we interested in computation of sub-transient current rather than steady 03
MARK sustained short-circuit current?
Q.1 (a) Explain advantages of per unit system for power system calculations. 03 (b) The Line currents in amperes in phases a, b, c respectively are 500 + j150, 100 – 04
j600 and -300 + j600 referred to the same reference vector. Find the symmetrical
(b) Following three generators are connected in parallel. 04 components of currents?
Generator G1 = 10 MVA, 10 kV, X” = 10%; (c) What is bus impedance matrix? Explain the method of fault calculation using bus 07
Generator G2 = 12 MVA, 10.6 kV, X” = 15%; impedance matrix.
Generator G3 = 15 MVA, 12 kV, X” = 20%.
Find the overall equivalent per unit reactance of these the system considering 20 Q.4 (a) What is the reason for transients during short circuit? 03
MVA, 11 kV system base.
(b) Prove that positive sequence and negative sequence impedance of fully transposed 04
(c) Three loads are connected in parallel across a 1400 V rms, 60 Hz single phase 07 transmission line are always equal.
supply as follows: (c) Using appropriate interconnection of sequence networks, derive the equation for a 07
Load 1: Inductive load, 125 kVA at 0.28 power factor line to line fault in a power system with faults impedance of 𝑍𝑓 .
Load 2: Capacitive load, 10 kW and 40 kvar OR
Load 3: Resistive load of 15 kW. Q.4 (a) What are symmetrical components and its need? 03
(i) Find the total kW, kvar,, kVA and the supply power factor (b) Explain in brief phase shift of symmetrical components in Y-∆ transformer banks. 04
(ii) Determine the kvar rating of a capacitor (of negligible resistance) and (c) Draw the waveforms for fault current for a 3-phase fault on alternator terminals. 07
capacitance in μF to improve the power factor to 0.8 lagging. Explain the sub-transient, transient and steady state reactance. What is their
(iii) Find the reduction in current after PF improvement. significance in fault calculations?

Q.2 (a) Why synchronous compensators can supply leading as well as lagging vars? 03 Q.5 (a) Explain methods to reduce corona loss in brief. 03
(b) Discuss why equivalent 𝜋 of a long line is preferred to the equivalent T circuit. 04 (b) Why the disruptive critical voltage is less than visual critical voltage. 04
(c) What is a receiving end power circle diagram? How can it be drawn? What 07 (c) Discuss the phenomenon of wave reflection and refraction. Derive expression for 07
information does it provide? reflection and refraction.
OR OR
(c) What is nominal circuit? Find ABCD constants for nominal 𝜋 and nominal T 07 Q.5 (a) Explain the phenomena of corona. 03
circuits of a transmission line? (b) State factors affecting corona loss and discuss in brief. 04
(c) Find the critical disruptive voltage and critical voltages for local and general corona 07
Q.3 (a) What is meant by doubling effect? Explain in brief. 03 on a 3-phase overhead transmission line, consisting of three stranded copper
(b) List various types of faults and write the relative frequency of occurrence of various 04 conductors spaced 2.5 m apart at the corners of an equilateral triangle. Air
types of faults. temperature and pressure are 210 C and 73 cm Hg respectively. The conductor
(c) A 4 bus network given in Fig. 1 with following positive, negative and zero sequence 07 diameter, irregularity factor and surface factor are 10.4 mm, 0.85, 0.7 and 0.8
reactances: respectively.
G1 : X0 = 0.06 pu; X1=X2 = 0.2 pu
G2: X0 = 0.05 pu; X1=X2 = 0.3 pu **********
T1 & T2 : X0 = X1=X2 = 0.2 pu
Transmission line: X0 = 0.08 pu; X1=X2 = 0.1 pu
G1 and G2 neutral ground reactance = 0.3 pu
A fault occurs at bus 4 phase R. Draw sequence impedance diagram and find the
fault current in p. u.

[PTO]
1 2
 Seat No.: ________ Enrolment No.___________

GUJARAT TECHNOLOGICAL UNIVERSITY

BE - SEMESTER–V (NEW) EXAMINATION – WINTER 2021
Subject Code:3150911 Date:23/12/2021
Subject Name:Power System- II
Time:02:30 PM TO 05:00 PM Total Marks: 70
Instructions:
1. Attempt all questions.
2. Make suitable assumptions wherever necessary.
3. Figures to the right indicate full marks.
4. Simple and non-programmable scientific calculators are allowed.
Q.4 (a) Draw zero sequence network of a three phase transformer with 03
(1) Star-Star connection with both neutrals grounded
Q.1 (a) Write a short note on Ferranti effect. 03 (2) Star delta connection with star side neutral grounded
(b) Two single phase loads having impedances 𝑍1 = 100 + 𝑗80 𝛺 04 (b) A 3-phase, 11 kV, 10 MVA synchronous generator has sequence 04
and 𝑍2 = 150 − 𝑗60 𝛺 are connected in parallel and this parallel reactances of 𝑋0 = 0.05 p.u., 𝑋1 = 𝑋2 = 0.15 p.u., . Assuming
combination is supplied from a source of 200 V a.c. Calculate: that the generator is initially operating at no load, calculate the
(1) Complex power drawn by each load magnitude of fault current in case of an L-G fault at generator
(2) Overall power factor of the combination as viewed from terminals.
the source. (c) Fig.(2) shows a power system network. The system data is given 07
(c) Explain working of a synchronous generator connected to infinite 07 in the table below.
bus. Draw equivalent circuit and phasor diagram.
Equipment MVA Voltage X1, X2, X0 ,
Q.2 (a) Explain classification of transmission lines. Define voltage 03 Rating Rating p.u. p.u. p.u.
regulation and efficiency of a transmission line. Gen-1 100 11 kV 0.25 0.25 0.05
(b) A balanced three phase load of 30 MW, 0.85 p.f. lagging is 04 Gen-2 100 11 kV 0.2 0.2 0.05
supplied at 132 kV, 50 Hz by overhead transmission line. The Transformer- 100 11/220 0.06 0.06 0.06
series impedance and shunt admittance of the line are (20 + 𝑗52) T1 kV
ohm and 𝑗3.15 x 10−4 siemen. Using nominal-T method, Transformer- 100 11/220 0.07 0.07 0.07
determine, T1 kV
(i) ABCD constants of the line Line 100 220 kV 0.1 0.1 0.3
(ii) Sending end voltage
(c) Derive equations of power flow through a transmission line. 07 Neutral point of generator-2 is grounded through a reactance of
OR 0.03 p.u. on generator base values.
(c) Explain rigorous solution of long transmission line 07 A single line to ground fault occurs at bus-2 of the network. Find
Q.3 (a) Show that symmetrical component transformation is power 03 the fault current.
invariant.
(b) Determine symmetrical components of phase-a voltages, 04
Va  2000  V, Vb  200245  V and Vc  200105  V
(c) Discuss transients on a transmission line in case of a symmetrical 07
fault.
OR
Q.3 (a) Draw equivalent circuits of a synchronous machine during (a) 03
sub-transient state (b) transient state and (c) steady state after
occurrence of a three phase fault on its terminals.
(b) Write a short note on selection of circuit breaker. 04
(c) A delta connected balanced resistive load is connected across an 07
unbalanced three phase supply as shown in fig. (1). The line OR
currents in phase A and B are given as, I A  1030  A and Q.4 (a) A power system network is shown in the single line diagram of 03
fig. (3). Draw zero sequence network for the system.
I B  15  60  A. Find the symmetrical components of line
current 𝐼𝐴 and delta current 𝐼𝐴𝐵 .

1 2
 Seat No.: ________ Enrolment No.___________

GUJARAT TECHNOLOGICAL UNIVERSITY

BE - SEMESTER–V (NEW) EXAMINATION – WINTER 2022
Subject Code:3150911 Date:11-01-2023
Subject Name:Power System- II
Time:10:30 AM TO 01:00 PM Total Marks:70
Instructions:
1. Attempt all questions.
(b) Explain analysis of a line to line fault. 04 2. Make suitable assumptions wherever necessary.
3. Figures to the right indicate full marks.
(c) A 3-phase synchronous generator rated 10 MVA, 11 kV delivers 07
4. Simple and non-programmable scientific calculators are allowed.
power to a static load through a line. Positive negative and zero MARKS
sequence impedances of the generator and line are mentioned in
the table below. Q.1 (a) Differentiate between Short, medium and long 03
Equipment X1, p.u. X2, p.u. X0, p.u. transmission lines and state how the method of analysis
Generator 0.2 0.2 0.05 differs in each type.
Line 0.1 0.1 0.3 (b) Three loads are connected in parallel across a 1400 V rms, 04
60 Hz, single phase a.c. supply.
The load draws 5 MW power at 10 kV at 0.8 p.f. lagging before a
line to ground fault takes place at load terminals. Determine the Load-1: Inductive load, 125 kVA at 0.28 power factor
fault current. Assume the generator neutral to be solidly grounded. Load-2: Capacitive load, 10 kW and 40 kvar
Q.5 (a) What is corona? Write formula of Disruptive critical voltage and 03 Load-3: Resisitive load of 15 kW
briefly describe each variable in the formula.
(b) What is insulation coordination? Define and explain BIL. 04 Find the total active, reactive and apparent power drawn
(c) What do you understand by “Travelling Waves” on transmission 07 from the supply and the overall power factor as viewed
lines? Derive equations showing relationship between voltage and from the supply side.
current in a forward wave and a backward wave on a lossless (c) Write a short note on per unit representation of 07
transmission line. transformers.
OR
Q.5 (a) A 3-phase, 220 kV, 50 Hz transmission line is 250 km long. 03 Q.2 (a) What is the reason behind occurrence of Ferranti Effect? 03
Calculate the corona loss occurring on the line if the radius of each How Ferranti effect can be prevented?
conductor is 11 mm and Equivalent spacing between conductors is (b) Draw phasor diagram for a short transmission line when 04
6 m. It is given that the relative density of air is 0.9456 and operating at
disruptive critical voltage is 118 kV per phase. (i) lagging power factor load
(b) Discuss recovery transients due to removal of a short circuit. 04 (ii) leading power factor load
(c) Explain types of lightning strokes. 07
Is it possible to have zero voltage regulation when
************* operating at some load? Explain.
(c) Explain Nominal-T and Nominal-π methods for analysis 07
of medium transmission lines.
OR
(c) Briefly discuss various methods of voltage control in 07
power systems.

Q.3 (a) Explain how the Breaking Capacity of a circuit breaker 03

can be calculated. Also explain how Fault MVA can be
calculated.
(b) Two synchronous generators in a power plant are 04
connected to a common bus bar. The generator ratings are
as follows.

Generator-1: 10 MVA, 11 kV, 𝑋𝑑" =40 %

Generator-2: 15 MVA, 11 kV, 𝑋𝑑" =60 %

3 1
 Determine fault current when a three phase fault takes (c) Explain the concept of Travelling Waves. 07
place at the bus bar while the generators were operating at OR
no load. Q.5 (a) Describe the factors affecting corona loss. 03
(c) Discuss: Transients on a transmission line during a short 07 (b) Explain the working of Thyrite valve type surge arresters 04
circuit. for protection against overvoltages.
OR (c) Explain reflection of a travelling wave in a line terminated 07
Q.3 (a) Explain any one type of modification in Bus Impedance 03 by:
Matrix due to addition of a branch or link in the network. (i) open circuit.
(b) A three bus power system has its 𝑍𝐵𝑈𝑆 matrix given as, 04 (ii) short circuit
𝑗0.25 𝑗0.1 𝑗0.15
𝑍𝐵𝑈𝑆 = [ 𝑗0.1 𝑗0.25 𝑗0.1 ] p.u. ************
𝑗0.15 𝑗0.1 𝑗0.15

A three phase fault occurs at bus-2 of the system.

Assuming all pre-fault voltages to be 1.0 p. u., determine,
(i) Fault current when a 3-phase fault occurs at bus-2
(ii) Voltage at bus-3 when the fault occurs on bus-2
(c) A synchronous generator rated 500 kVA, 440 V with a 07
sub-transient reactance of 0.25 p.u. is supplying a static
load of 400 kW at 0.8 p.f. lagging at rated terminal
voltage. A three phase fault occurs at the generator
terminals. Determine:
(i) e.m.f. behind transient reactance
(ii) symmetrical short circuit current during sub-
transient stage

Q.4 (a) If 𝛼 is a complex operator such that 𝛼 = 𝑒 𝑗120° , then 03

evaluate the following terms:
(i) 𝛼2 − 1
(ii) 1 − 𝛼 − 𝛼2
(b) Explain Symmetrical Component Transformation 04
(c) Explain analysis of a line to ground fault. 07
OR
Q.4 (a) Draw zero sequence networks of three phase transformers 03
with the following connections.
(i) ∆ − 𝑌 connection with star side neutral
isolated
(ii) 𝑌 − 𝑌 connection with any one side neutral
solidly grounded
(b) Explain analysis of a line to line fault. 04
(c) A three phase synchronous generator rated 11 kV, 50 07
MVA has positive, negative and zero sequence reactances
as 0.2 p.u., 0.1 p.u. and 0.05 p.u. respectively with
machine ratings as base values. The generator is star
connected with the neutral point solidly grounded. Find
the magnitude of fault current in the event of a:
(i) Three phase fault
(ii) Line to ground fault
at generator terminals. Assume generator at no load prior
to fault.

Q.5 (a) Describe methods to reduce corona loss. 03

(b) Discuss switching transients in an R-L circuit(power 04
system) supplied by an a.c. source.

2 3