DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING
SEM: V
UNIT I
INTRODUCTION
PART A
1.
State the
applications of HVDC transmission system.
2.
List out the various devices used in FACTS.
3.
What is meant by
STATCOM?
4.
Why high voltage is
preferred for power transmission?
5.
State the advantage
of EHV AC transmission system.
6.
Name some HVDC
system in India.
7.
What is the
electric power supply system?
8.
What is the level
of voltage for HVDC transmission?
9.
State the
disadvantages of HVDC transmission.
10.
Which factors
affect sag in the transmission line?
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PART B
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1.
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a) Draw and explain the structure of modern
power system including the voltage level in each
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transmission levels.
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(8)
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b) Write short notes on SVC.
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(8)
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2.
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Derive expressions for sag and tension in a
power conductor strung between two supports at
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equal heights taking into account the wind and
ice loadings also.
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(16)
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3.
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Explain in detail the types of FACTS
controllers.
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(16)
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4.
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a) Draw and explain the
structure of modern electric power system with various voltage levels.
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(12)
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b) Draw a simple model of UPFC.
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(4)
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5.
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Discuss various types of HVDC links. Mention
any one HVDC link available in India with rating.
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(16)
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6.
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a) What are the advantages
of high transmission voltage for the transmission of electric power?
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Explain.
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(8)
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b) A
50 km long
transmission line supplies
a load of
5 MVA at
0.8 pf lagging
at 33 kV.
The
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efficiency of transmission is 90 %. Calculate
the volume of Al conductor required for the line
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when 3-phase, 3 wire system is used. The
specific resistance of Al is 2.85 x 10-8 Ω-m.
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(8)
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a) Discuss various types of HVDC links.
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(8)
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b) List out the main components of a HVDC
system.
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(8)
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8.
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Draw and explain the
structure of modern power systems with typical voltage levels. What is the
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highest VDH level available in India?
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(16)
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9.
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a) Give the advantages of HVDC transmission
over HVAC transmission system.
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(8)
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b) Explain why the transmission of electric power is carried at high
voltage. Give the reasons. (8)
10.
Compare the
HVDC transmission with
EHVAC transmission in
the following respects.
(i)
Economics of
transmission (ii) Reliability (iii) Technical Performance. (16)
UNIT II
TRANSMISSION LINE PARAMETERS
PART A
1.
State the
advantages of ACSR conductors when used for overhead lines.
2.
What is skin
effect?
3.
What is ACSR
conductor?
4.
Mention the
advantages of bundled conductors.
5.
On what factor does
the skin effect depend?
6.
What is the
bundling of conductors?
7.
What is meant by
‘Corona’? Mention their effects.
8.
What is meant by
proximity?
9.
Define visual
critical voltage.
10.
Distinguish between
stranded and bundled conductors.
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PART B
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1.
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a) Describe the atmospheric and electrical
factors affecting corona loss.
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(8)
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b) A three phase, 50 Hz, 220 kV transmission
line consists of conductors of 2 cm diameter and
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spaced equilaterally at a
distance of 4 m. The line conductors have smooth surface with value of
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surface irregularity factor
0.96. The barometric pressure is 73 cm of Hg and temperature of 20o
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C. Determine the fair and stormy weather corona
loss per km per phase.
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(8)
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2.
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a) Explain an expression for the loop
inductance of a single phase line.
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(8)
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b) A single phase transmission line has two
parallel conductors 3 m apart, the radius of each
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conductor being 1 cm.
Calculate the loop inductance per km length of the line if the material of
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the conductance is (1) copper (2) steel with
relative permeability of 100.
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(8)
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3.
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a) Derive an expression for
capacitance of a 3-phase line when the conductors are symmetrically
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placed.
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(8)
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b) Calculate
the capacitance of a 100
km long 3-phase,
50 Hz overhead
transmission line
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consisting of
3 conductors each
of diameter 2
cm and spaced
2.5 m at
the corners of
an
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equilateral triangle.
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(8)
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4.
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a) Discuss the advantages and disadvantages of
corona.
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(8)
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b) A 3 phase transmission line is having three
conductors equilaterally spaced 6 m apart. The
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diameter of each conductor is 2 cm. the air
temperature is 270C and pressure is 72 cm of Hg. If
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the surface
factor is 0.82
and irregularity factor
is 0.9, find
the critical disruptive
and visual
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critical disruptive voltages.
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(8)
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5.
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Derive an expression for
inductance of a 3 phase transmission line with unsymmetrical spacing.
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(16)
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6.
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From the
fundamental derive an
expression for inductance
of a single
phase transmission
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system.
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(16)
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7.
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Derive an
expression for capacitance
of a single
phase transmission system
and discuss the
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effect of earth on capacitance with suitable
equation.
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(16)
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8.
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a) Write short note on Proximity effect.
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(8)
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b)
A 400 kV, 3 phase bundled conductor line with two sub-conductor per
phase has a horizontal configuration as shown in figure. The radius of each
sub-conductor is 1.6 cm. (1) Find the inductance per phase per km of the line
(2) Compute the inductance of the line with only one conductor per phase having
the same cross-sectional area of the conductor of each phase. (8)
9.
a) Derive an
expression for capacitance of a single phase overhead transmission system. (8)
b)
A 3-phase, 50 Hz, 132 kV overhead line has conductors placed in a
horizontal plane 4 m apart. Conductor diameter is 2 cm. if the line length is
100 km, calculate the charging current per
phase assuming complete transposition. (8)
10.
a) Derive the
equation for capacitance of 3-phase unsymmetrically spaced overhead lines. (8)
b) Find out the capacitance of a single
phase line of 30 km long consisting of two parallel wires
each 15 mm diameter and 1.5 m apart. (8)
UNIT III
MODELLING AND PERFORMANCE OF TRANSMISSION LINES
PART A
1.
Mention the
approximate value of single impedance for overhead line.
2.
Define transmission
efficiency.
3.
Draw the phasor
representation of short transmission line.
4.
For controlling
reactive power, what adjustment should be done in transformer present in the
system?
5.
Define surge
impedance.
6.
Classify
transmission line based on its length.
7.
Draw the nominal π
representation of a transmission line.
8.
What is the Surge
Impedance Loading?
9.
What is the power
circle diagram?
10.
What is the
Ferranti effect?
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PART B
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1.
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Derive expressions
for regulation and
efficiency of a
short transmission line.
Draw required
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circuit and phasor diagram.
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(16)
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2.
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a) Explain the classification of lines based on
their length of transmission.
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(8)
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b) A short 3-phase transmission line with an
impedance of (6+j8) Ω per phase has sending and
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receiving end voltages of 120 kV and 110 kV
respectively for some receiving end load at a pf of
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0.9 lagging. Determine power output and sending
end power factor.
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(8)
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3.
A short 3 phase
transmission line has series line impedance per phase of (20+j50) Ω. The line
delivers a load of 50 MW at 0.7 pf lag. Determine the regulation of the line
and the A, B, C, D
parameters of the line. If the same load is delivered at 0.7 pf lead,
determine the regulation of the line. System voltage 220 kV. (16)
4. The A, B, C, D
constants of a 3 phase transmission line are A = D = 0.936+j0.016, B = 33.5 +
j1.138 Ω, C = (-0.928+j901.223) x 10-6 S. The load at the receiving end is 40 MW at 220 kV with power factor
at 0.86 lagging. Find the magnitude of the sending end voltage, current, power,
line efficiency and the voltage regulation. Assume the magnitude of sending end
voltage remains constant. (16)
5.
Determine the efficiency and regulation of a 3-phase, 100 km, 50 Hz
transmission line delivering 20 MW at a power factor of 0.8 pf lagging and 66
kV to a balanced load. The conductors are of copper, each having resistance 0.1
Ω / km, and 1.5 cm outside dia, spaced equilaterally 2 m
between centers. Use nominal T method. (16)
6. A three phase 5
km long transmission line having resistance of 0.5 Ω/km and inductance of 1.76
mH/km is delivering power at 0.8 pf lagging. The receiving end voltage is 32
kV. If the supply end voltage is 33 kV, 50 Hz, find line current, regulation
and efficiency of the transmission line. (16)
7.
A 3-phase, 50 Hz, 100 km long overhead line has the following line
constants: resistance per phase per km = 0.153 Ω, inductance per phase per km =
1.21 mH, capacitance per phase per km
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= 0.00958 μF. The line supplies a load of 20 MW
at 0.9 pf lagging at a line voltage of 110 kV at
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the receiving end. Use
nominal π representation; calculate sending end voltage, current, power
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factor, regulation and efficiency.
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(16)
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8.
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a) What is Ferranti effect? Explain them with
phasor diagram.
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(8)
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b) A 50 Hz, 3 phase
transmission line 30 km long has a total series impedance of (40+j125) Ω and
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shunt admittance of 10-3 S. The
load is 50 MW at 220 kV with 0.8 pf lag. Find the sending end
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voltage, current and power factor. Use nominal
π method.
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(8)
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9.
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A 15
km long overhead
line delivers 5
MW at 11
kV at 0.8
pf lag line
loss is 12%
of power
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delivered. Line
inductance is 1.1
mH per km
per phase. Find
the sending end
Voltage and
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regulation.
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(16)
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10.
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a) Explain the surge
impedance loading with respect to an overhead transmission line.
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(8)
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b) Explain the end condenser method for medium
transmission line.
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(8)
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UNIT IV
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INSULATORS AND CABLES
PART A
1.
What is necessity
of grading of an underground cable?
2.
Draw the equivalent
circuit of a cable.
3.
Define string
efficiency.
4.
Why the potential
distribution across the string units of insulator is not uniform?
5.
State the
advantages of polymeric insulators over porcelain insulators.
6.
Show that
insulation resistance of cable is inversely proportional to its length.
7.
Name any four
insulating material used for making underground cable.
8.
What are the
various methods of improving string efficiency?
9.
Give the
classification of cable for single and three phase service with operating
voltages.
10.
Write down the
expression for insulation resistance of a single core cable.
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PART B
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1.
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a) Explain with suitable sketch, pin type and
suspension type insulators.
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(8)
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b) A string of eight suspension
insulators is to be fitted with a grading ring. If the pin to earth
capacitances is all equal to C, find the values of line to pin capacitances
that would give a uniform voltage distribution over the string. (8)
2. a) Prove that
the ratio of voltage gradient with and without intersheath will be 2/(1+α),
when there is only one layer of intersheath. (Ratio of intersheath radius to
core radius = outer sheath radius to intersheath radius = α). (8)
b) A single core cable has a conductor of diameter 3 cm and inside
diameter of lead sheath is 6 cm. If the cable is designed for operating voltage
of 33 kV (line to neutral), find
(1) Maximum
and minimum values of electric stress
(2) Optimal value of conductor radius for
the smallest value of the maximum stress. (8)
3.
In a 33 kV overhead
line, there are three units in the string of insulators. If the capacitance
between each insulator pin and earth is 11% of self capacitance of each
insulator, find the distribution of voltage over 3 insulators and string
efficiency. Draw the equivalent circuit. (16)
4.
A single core cable of conductor diameter 2 cm and lead sheaths of
diameter 3.1 cm and 4.2 cm
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are introduced between the core and lead
sheath. If the maximum stress in the layers is the
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same, find the voltages on the inter sheath.
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(16)
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5.
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Elaborate the various methods to improve the
string efficiency.
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(16)
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6.
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What is grading of cables? Describe two
methods.
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(16)
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7.
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An insulator string for 66 kV line has 4 discs. The
shunt capacitance between each joint and
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metal work is 10 % of the capacitance of each
disc. Find the voltage across the different discs
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and string efficiency.
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(16)
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8.
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a) With a neat sketch explain the construction
of pin type insulator.
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(8)
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b) Compare power transmission using overhead
line and underground cable.
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(8)
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9. Define ‘string efficiency’ and calculate its value for a string of
three insulator units if the capacitance of each unit to earth and line be 20%
and 5% of the self capacitance of the unit. (16)
10.
A 66 kV, single
core metal sheathed cable is to be graded by means of a metallic inter sheath.
Calculate the diameter of the inter sheath and the voltage at which it must be
maintained in
order to obtain minimum overall diameter. The maximum voltage gradient
at which the insulating material can be worked is 60 kV/cm. Derive the formula
used. (16)
UNIT V
SUBSTATION, GROUNDING SYSTEM AND DISTRIBUTION SYSTEM
PART A
1.
How will you select
an ideal location for a distribution substation?
2.
State the
advantages of ring main distribution system over radial system.
3.
List out the
disadvantages of single bus scheme.
4.
What is the role of
circuit breaker in power system?
5.
Write down the
difference between disconnector switch and isolator.
6.
Based on what
criteria the substation bus schemes are chosen.
7.
Name the factor
that should be taken care of while designing and erecting a sub-station.
8.
Give the different
type of the bus-bar arrangement used in sub-stations.
9.
What is the
interconnect system?
10.
List the type of
sub-stations.
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PART B
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1.
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What are the various methods of neutral
grounding? Elaborate any two.
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(16)
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2.
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Describe the following substation bus schemes
with suitable diagram.
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a.
Double bus with double breaker.
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(8)
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b. Double
bus with single breaker.
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(8)
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3.
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Explain the following connection schemes of
distribution system.
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a.
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Radial system.
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(8)
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b.
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Inter connected system.
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(8)
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4.
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Describe any four types of substation bus
schemes.
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(16)
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5.
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Discuss and
compare Radial and
Ring main distribution system.
What
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is the
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role
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of
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interconnectors in distribution system?
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(16)
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6.
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Explain the following:
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a.
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Neutral grounding.
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(8)
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b.
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Resistance grounding.
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(8)
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7.
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Explain with neat diagram any two bus-bar
arrangements used in sub-station.
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(16)
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8.
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Explain the following substation bus schemes.
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a.
Double bus with double breaker.
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(8)
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b.
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Main and transfer bus.
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(8)
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9. a) With neat diagrams explain the different
types of bus bar arrangements used in substations.
(8)
b) With
neat layout and schematic connection explain the pole mounted sub-station. (8)
10. a) Explain the
various systems of ac distribution. (8)
b) Explain the ring main system of distribution with interconnector.
What is the purpose of interconnector? (8)
