T&D Notes

1. EE8402 Syllabus Transmission and Distribution
UNIT I TRANSMISSION LINE PARAMETERS 9
Structure of Power System – Parameters of single and three phase transmission lines
with single and double circuits -Resistance, inductance and capacitance of solid,
stranded and bundled conductors, Symmetrical and unsymmetrical spacing and
transposition – application of self and mutual GMD; skin and proximity effects -Typical
configurations, conductor types and electrical parameters of EHV lines.
UNIT II MODELLING AND PERFORMANCE OF TRANSMISSION LINES 9 EE8402
Syllabus Transmission and Distribution
Performance of Transmission lines – short line, medium line and long line – equivalent
circuits, phasor diagram, attenuation constant, phase constant, surge impedance –
transmission efficiency and voltage regulation, real and reactive power flow in lines –
Power Circle diagrams – Formation of Corona – Critical Voltages – Effect on Line
Performance.
UNIT III MECHANICAL DESIGN OF LINES 9 EE8402 Syllabus Transmission and
Distribution
Mechanical design of OH lines – Line Supports –Types of towers – Stress and Sag
Calculation – Effects of Wind and Ice loading. Insulators: Types, voltage distribution in
insulator string, improvement of string efficiency, testing of insulators.
UNIT IV UNDER GROUND CABILITYS 9 EE8402 Syllabus Transmission and
Distribution
Underground cabilitys – Types of cabilitys – Construction of single core and 3 core
Cabilitys – Insulation Resistance – Potential Gradient – Capacitance of Single-core and
3 core cabilitys – Grading of cabilitys – Power factor and heating of cabilitys– DC
cabilitys.
UNIT V DISTRIBUTION SYSTEMS 9 EE8402 Syllabus Transmission and
Distribution
Distribution Systems – General Aspects – Kelvin’s Law – AC and DC distributions –
Techniques of Voltage Control and Power factor improvement – Distribution Loss –
Types of Substations -Methods of Grounding – Trends in Transmission and Distribution:
EHVAC, HVDC and FACTS (Qualitative treatment only).

2. UNIT I TRANSMISSION LINE PARAMETERS
Structure of Power System – Parameters of single and three phase transmission lines
with single and double circuits -Resistance, inductance and capacitance of solid,
stranded and bundled conductors, Symmetrical and unsymmetrical spacing and
transposition – application of self and mutual GMD; skin and proximity effects -Typical
configurations, conductor types and electrical parameters of EHV lines.
Structure of Power System
Generatingstations,transmissionlines andthe distributionsystems are the maincomponentsof an
electricpowersystem. Generatingstations andadistributionsystemare connected through
transmissionlines,whichalsoconnectone powersystem(grid,area) toanother.A distributionsystem
connectsall the loadsina particularareato the transmissionlines.
1. GeneratingSubsystem
Thisincludesgeneratorsandtransformers.

3. 1. Generators – An essential component of power systems is the three phase ac generator known
as synchronous generator or alternator. Synchronous generators have two synchronously
rotating fields: One field is produced by the rotor driven at synchronous speed and excited by dc
current. The other field is produced in the stator windings by the three-phase armature
currents. The dc current for the rotor windings is provided by excitation systems. In the older
units, the exciters are dc generators mounted on the same shaft, providing excitation through
slip rings. Current systems use ac generators with rotating rectifiers, known as brushless
excitation systems. The excitation system maintains generator voltage and controls the reactive
power flow. Because they lack the commutator, ac generators can produce high power at high
voltage,typically30 kV.
2. Transformers –
The transformer transfers power with very high efficiency from one level of voltage to an
additional level. The power transferred to the secondary is almost the same as the primary,
excluding for losses in the transformer. Using a step-up transformer will reduce losses in the
line, which makes the transmission of power over long distances possible. Insulation
requirements and other practical design problems limit the generated voltage to low values,
usually 30 kV. Thus, step-up transformers are used for transmission of power. At the receiving
end of the transmission lines step-down transformers are used to reduce the voltage to suitable
values for distribution or utilization. The electricity in an electric power system may undergo
fouror five transformationsbetweengeneratorandconsumers.
3. Transmissionand Sub transmissionSubsystem
An overhead transmission network transfers electric power from generating units to the
distribution system which ultimately supplies the load. Transmission lines also interconnect
adjacent utilities which allow the economic dispatch of power within regions during normal
conditions, and the transfer of power between regions during emergencies. Standard
transmission voltages are established in the United States by the American National Standards
Institute (ANSI). Transmission voltage lines operating at more than 60 kV are standardized at 69
kV, 115 kV, 138 kV, 161 kV, 230 kV, 345 kV, 500 kV, and 765 kV line-to-line. Transmission
voltages above 230 kV are usually referred to as extra-high voltage (EHV). High voltage
transmission lines are terminated in substations, which are called high-voltage substations,
receiving substations, or primary substations. The function of some substations is switching
circuits in and out of service; they are referred to as switching stations. At the chief substations,
the voltage is stepped down to a value more suitable for the next part of the trip toward the
load.Verylarge industrial customersmaybe servedfromthe transmissionsystem
4. Distribution Subsystem
The distribution system connects the distribution substations to the consumers’ service-
entrance equipment. The primary distribution lines from 4 to 34.5 kV and supply the load in a

4. well-defined geographical area. Some small industrial customers are served directly by the
primaryfeeders.
Parameters of single and three phase transmission lines with single and double
circuits
A transmission line has resistance, inductance and capacitance uniformly
distributed along the whole length of the line.
Resistanceofa TransmissionLine
The resistance of transmission line conductors is the most important cause of
power loss in a transmission line. The resistance R of a line conductor having
resistivity ρ, length l and area of cross-sectiona is given by ;
R = ρ l/a
The variation of resistance of metallic conductors with temperature is practically
linear over the normal range of operation. Suppose R1 and R2are the resistances of
a conductor at t1 ºC and t2 ºC ( t2 > t1 ) respectively. If α 1is the temperature

5. coefficient at t1 °C, then,
Inductance of a Single Phase Two-Wire Line
A single phase lineconsistsof twoparallelconductorswhichformarectangularloopof one turn.
INDUCTANCE OF A SINGLE PHASE TWO-WIRE LINE
A single phase line consists of two parallel conductors which form a rectangular
loop of one turn.
When an alternating current flows through such a loop, a changing magnetic flux
is set up. The changing flux links the loop and hence the loop (or single phase line)
possesses inductance. It may appear that inductance of a single phase line is
negligible because it consists of a loop of one turn and the flux path is through air
of high reluctance. But as the X –sectional area of the loop is very **large, even

6. for a small flux density, the total flux linking the loop is quite large and hence the
line has appreciable inductance.
Consider a single phase overhead line consisting of two parallel conductors A and
B spaced d metres apart as shown in Fig. Conductors A and B carry the same
amount of current ( i.e. IA = IB ), but in the opposite direction because one forms
the return circuit of the other. IA+IB = 0
In order to find the inductance of conductor A (or conductor B), we shall have to
consider the flux linkages with it. There will be flux linkages with conductor A due
to its own current IA and also A due to the mutual inductance effect of current IB in
the conductorB Flux linkages with conductorA due to its own current
Flux linkages with conductorA due to current IB
Total flux linkages with conductor A is

7. Note that eq. ( ii) is the inductance of the two-wire line and is sometimes called
loop inductance. However, inductance given by eq. ( i) is the inductance per
conductorand is equal to half the loop inductance.
Note that eq. ( ii) is the inductance of the two-wire line and is sometimes called loop
inductance. However, inductance given by eq. ( i) is the inductance per conductor and is equal to
half the loop inductance.
1. INDUCTANCE OF A 3-PHASE OVERHEAD LINE
Fig. shows the three conductors A, B and C of a 3-phase line carrying currents IA ,
IB and IC respectively. Let d 1 , d2 and d3 be the spacings between the conductors
as shown. Let us further assume that the loads are balanced i.e. IA + IB + IC = 0.
Consider the flux linkages with conductor There will be flux linkages with
conductor A due to its own current and also due to the mutual inductance effects of
IB and IC

8. 2. SYMMETRICAL SPACING
If the three conductors A, B and C are placed symmetrically at the corners of an
equilateral triangle of side d, then, d1 = d2 = d3 = d. Under such conditions, the
flux Derived in a similar way, the expressions for inductance are the same for
conductors B and C.
3. UNSYMMETRICAL SPACING
When 3-phase line conductors are not equidistant from each other, the conductor
spacing is said to be unsymmetrical. Under such conditions, the flux linkages and
inductance of each phase are not the same. A different inductance in each phase
results in unequal voltage drops in the three phases even if the currents in the
conductors are balanced. Therefore, the voltage at the receiving end will not be the
same for all phases. In order that voltage drops are equal in all conductors, we

9. generally interchange the positions of the conductors at regular intervals along the
line so that each conductor occupies the original position of every other conductor
over an equal distance. Such an exchange of positions is known as transposition.
Fig.shows the transposed line. The phase conductors are designated as A, B and C
and the positions occupied are numbered 1, 2 and 3. The effect of transposition is
that each conductorhas the same average inductance.
Considering all the three sections of the transposed line for phaseA

10. If we compare the formula of inductance of an un symmetrically spaced transposed
line with that of symmetrically spaced line, we find that inductance of each line
conductorin the two cases will be equal if
𝑑 = √ 𝑑1 𝑑2 𝑑3
3
where d is the distanced is known as equivalent equilateral
spacing for un symmetrically transposed line.
STRANDED AND BUNDLED CONDUCTORS
SPIRALING AND BUNDLE CONDUCTOR EFFECT

11. There are two types of transmission line conductors: overhead and underground.
Overhead conductors, made of naked metal and suspended on insulators, are
preferred over underground conductors because of the lower cost and easy
maintenance. Also, overhead transmission lines use aluminum conductors, because
of the lower cost and lighter weight compared to copper conductors, although more
cross-section area is needed to conduct the same amount of current. There are
different types of commercially available aluminum conductors: aluminum-
conductor-steel-reinforced (ACSR), aluminum-conductor-alloy-reinforced
(ACAR), all-aluminum-conductor (AAC), and all-aluminumalloy- conductor
(AAAC).
CSR is one of the most used conductors in transmission lines. Itconsists of
alternate layers of stranded conductors, spiraled in opposite directions to hold
the strands together, surrounding a coreof steel strands. Figureaboveshows an
example of aluminum and steel strands combination. The purposeof introducing
a steel core inside the stranded aluminum conductors is to obtain a high strength-
to-weight ratio. A stranded conductor offers moreflexibility and easier to
manufacturethan a solid large conductor. However, the total resistance is
increased because the outsidestrands are larger than the inside strands on
account of the spiraling. The resistance of each wound conductor at any layer, per
unit length, is based on its total length as follows:

12. CONCEPTOF SELF-GMD AND MUTUAL-GMD
The use of self geometrical mean distance (abbreviated as self-GMD) and
mutual geometrical mean distance (mutual-GMD) simplifies the inductance
calculations, particularly relating to multi conductorarrangements.
i) Self-GMD (Ds)
In order to have concept of self-GMD (also sometimes called Geometrical mean
radius; GMR), consider the expression for inductance per conductor per metre
already derived in Art. Inductance/conductor/m
In this expression, the term 2 × 10-7 × (1/4) is the inductance due to flux within
the solid conductor. For many purposes, it is desirable to eliminate this term by
the introduction of a concept called self-GMD or GMR. If we replace the original
solid conductor by an equivalent hollow cylinder with extremely thin walls, the
current is confined to the conductor surface and internal conductor flux linkage
would be almost zero. Consequently, inductance due to internal flux would be
zero and the term 2 × 10-7 × (1/4) shall be eliminated. The radius of this
equivalent hollow cylinder must be sufficiently smaller than the physical radius of
the conductor to allow room for enough additional flux to compensate for the
absence of internal flux linkage. It can be proved mathematically that for a solid

13. round conductor of radius r, the self-GMD or GMR = 0·7788 r. Using self-GMD, the
eq. ( i) becomes :
Inductance/conductor/m=2 × 10-7loge d/Ds *
Where
Ds = GMR or self-GMD = 0·7788 r
self-GMD of a conductor depends upon the size and shape of the conductor and is
independent of the spacing between the conductors.
ii) Mutual-GMD
he mutual-GMD is the geometrical mean of the distances form one conductor to
the other and, therefore, must be between the largest and smallest such distance. In
fact, mutual-GMD simply represents the equivalent geometrical spacing.
(a) The mutual-GMD between two conductors (assuming that spacing between
conductors is large compared to the diameter of each conductor) is equal to the
distance between their centres i.e. Dm = spacing between conductors = d
(b) For a single circuit 3-φ line, the mutual-GMD is equal to the equivalent
equilateral spacing i.e., ( d1 d2 d3 )1/3
.

14. (c) The principle of geometrical mean distances can be most profitably
employed to 3-φ double circuit lines. Consider the conductor arrangement of the
double circuit shown in Fig. Supposethe radius of each conductoris r.
Self-GMD of conductor= 0·7788 r
Self-GMD of combination aa’ is
mutual GMD depends only upon the spacing and is substantially independent of
the exact size, shape and orientation of the conductor.
Inductance Formulas in Terms of GMD
The inductance formulas developed in the previous articles can be conveniently
expressed in terms of geometrical mean distances.

15. Types ofConductor
The most commonly used conductor materials for over head lines are copper,
aluminium, steel cored aluminium, galvanised steel and cadmium copper. The
choice of a particular material will depend upon the cost, the required electrical
and mechanical properties and the local conditions. All conductors used for
overhead lines are preferably stranded in order to increase the flexibility. In
stranded conductors, there is generally one central wire and round this, successive
layers of wires containing 6, 12, 18, 24 ...... wires. Thus, if there are n layers, the
total number of individual wires is 3n(n + 1) + 1. In the manufacture of stranded
conductors, the consecutive layers of wires are twisted or spiralled in opposite
directions so that layers are bound together.
1.Copper
Copper is an ideal material for overhead lines owing to its high electrical
conductivity and greater tensile strength. It is always used in the hard drawn form
as stranded conductor. Although hard drawing decreases the electrical conductivity
slightly yet it increases the tensile strength considerably. Copper has high current
density i.e., the current carrying capacity of copper per unit of Xsectional area is
quite large. This leads to two advantages. Firstly, smaller X-sectional area of

16. conductor is required and secondly, the area offered by the conductor to wind loads
is reduced. Moreover, this metal is quite homogeneous, durable and has high scrap
value. There is hardly any doubt that copper is an ideal material for transmission
and distribution of electric power. However, due to its higher cost and non-
availability, it is rarely used for these purposes. Now a days the trend is to use
aluminium in place of copper.
2. Aluminium
Aluminium is cheap and light as compared to copper but it has much smaller
conductivity and tensile strength. The relative comparison of the two materials is
briefed below:
(i) The conductivity of aluminium is 60% that of copper. The smaller conductivity
of aluminium means that for any particular transmission efficiency, the X-sectional
area of conductor must be larger in aluminium than in copper. For the same
resistance, the diameter of aluminium conductor is about 1·26 times the diameter
of copper conductor. The increased X-section of aluminium exposes a greater
surface to wind pressure and, therefore, supporting towers must be designed for
greater transverse strength. This often requires the use of higher towers with
consequenceof greater sag.
(ii) The specific gravity of aluminium (2·71 gm/cc) is lower than that of copper
(8·9 gm/cc).Therefore, an aluminium conductor has almost one-half the weight of
equivalent copper conductor. For this reason, the supporting structures for
aluminium need not be made so strong as that of copperconductor.
(iii) Aluminium conductor being light, is liable to greater swings and hence larger
cross-arms are required.
(iv) Due to lower tensile strength and higher co-efficient of linear expansion of
aluminium, the sag is greater in aluminium conductors. Considering the combined
properties of cost, conductivity, tensile strength, weight etc., aluminium has an
edge over copper. Therefore, it is being widely used as a conductor material. It is
particularly profitable to use aluminium for heavy-current transmission where the
conductor size is large and its cost forms a major proportion of the total cost of
complete installation.

17. 3. Steelcored aluminium
Due to low tensile strength, aluminium conductors produce greater sag. This
prohibits their use for larger spans and makes them unsuitable for long distance
transmission.In order to increase the tensile strength, the aluminium conductor is
reinforced with a core of galvanised steel wires. The composite conductorthus
obtained is known as steel cored aluminium and is abbreviated as A.C.S.R.
(aluminium conductorsteel reinforced).
Steel-cored aluminium conductor consists of central core of galvanized steel wires
surrounded by a number of aluminium strands. Usually, diameter of both steel and
aluminium wires is the same. The X-section of the two metals are generally in the
ratio of 1 : 6 but can be modified to 1 : 4 in order to get more tensile strength for
the conductor. Fig. shows steel cored aluminium conductor having one steel wire
surrounded by six wires of aluminium. The result of this composite conductor is
that steel core takes greater percentage of mechanical strength while aluminium
strands carry the bulk of current. The steel cored aluminium conductors have the
following
Advantages:
(i) The reinforcement with steel increases the tensile strength but at the same time
keeps the composite conductor light. Therefore, steel cored aluminium conductors
will producesmaller sag and hence longer spans can be used.
(ii) Due to smaller sag with steel cored aluminium conductors, towers of smaller
heights can be used.

18. 4. Galvanisedsteel
Steel has very high tensile strength. Therefore, galvanised steel conductors
can be used for extremely long spans or for short line sections exposed to
abnormally high stresses due to climatic conditions. They have been found very
suitable in rural areas where cheapness is the main consideration. Due to poor
conductivity and high resistance of steel, such conductors are not suitable for
transmitting large power over a long distance. However, they can be used to
advantage for transmitting a small power over a small distance where the size of
the copper conductor desirable from economic considerations would be too small
and thus unsuitable for use because of poormechanical strength.
5. Cadmium copper
The conductor material now being employed in certain cases is copper alloyed
with cadmium. An addition of 1% or 2% cadmium to copper increases the tensile
strength by about 50% and the conductivity is only reduced by 15% below that of
pure copper. Therefore, cadmium copper conductor can be useful for exceptionally
long spans. However, due to high cost of cadmium, such conductors will be
economical only for lines of small X-section i.e., where the cost of conductor
material is comparatively small compared with the costof supports.
UNIT-1 TRANSMISSION LINE PARAMETERS
PART A
1. Write the transmission and distribution voltage levels in India. APRIL/MAY 2015 (R8) (or)
Mention the transmission voltages that followed in tamilnadu. (May 2017)
The voltage levels in use in TNEB are 400KV, 230 KV, 110 KV, 66 KV,33 KV, 22 KV and 11 KV.
In order to evacuate bulk power from one region to another region, there is a more scope for
enhancing transmission capability to 765 KV level and setting up of 800 KV High Voltage DC
system.
2. Write the various factors affecting the corona loss. NOV/DEC 2011 (R8)
Corona loss depends upon numerous factors like system frequency, system voltage, air density;
surface and size of conductor etc. .. When potential difference increase the electric field increases
and therefore powerloss due to corona increases.
3. Differentiate between bundled conductors and stranded conductors. NOV/DEC 2007

19. Stranded conductors Bundled conductors
Stranded conductors are composed of two
or more elements of strands electrically in
parallel with alternate layers spiralled in
opposite direction to prevent unwinding.
A bundled conductor is a conductor made
up of two or more sub-conductors and is
used as single phase conductor. Bundled
conductors are separated from each other
by 30 cm or more and conductors of each
phase are connected by connecting wires at
particular length.
It is used for voltages less than 230 kV. It is used for voltages above 230 kV.
4. Define ACSR.
ACSR is aluminium conductor with steel reinforcement. This conductor is low tensile strength of
aluminium conductors is made up by providing central strands of high tensile strength galavanised
steel.such conductor is known as ACSR. Therefore this conductor reduces the corona losses and used
in long transmission lines.
5. Explain the advantages of ACSR conductors when used for overhead lines.
Cheaper and lighter than copper.
Low density and low conductivity, which increases diameter of conductor.
Increases flexibility.
6. State the skin effect in transmission line .mention its effect on the resistance of the line. (May
2017) What is skin effect? (Dec 2016)
Skin effect is the tendency for alternating current (AC) to flow mostly neat the outer surface of a
conductor which causes non-uniform distribution of current. Thus the current density is largest near
the surface of the conductor and decreases with greater depth inside the conductor .the effect
becomes more and more apparent as the frequency increases
Due to reduction in effective area of cross section offered to the follow of the current through the
conductor, the resistance of the conductor increases.
7. State the different types of overheads conductors. (May 2017)
Hard drawn copper conductor
Steel cored copper conductor
Cadmium copper conductor.
Copper welded conductor.
All aluminium conductors.
Aluminium conductor with steel reinforcement
All Aluminium alloy conductor
ACAR conductor
Phosphor bronze conductor
Alumoweld conductor

20. Galvanized steel conductor
8. What are the advantages of bundled conductors ?(Dec 2016)
Increases the capacitance.
Increases the power capability of the line.
Reduces the voltage surface gradient.
Reduces corona loss.
Reduces radio interference.
9. What is transposition? Why are the transmission line transposed? (Dec 2017)
Define transposition? (May 2016)
Transposition is the periodic swapping of position of the conductors of a transmission lines, so that
each conductor occupies the original position of every other conductor over a equal distance so as to
achieve balance in the three phases
10. What is corona? (May 2016)
When the potential difference is increased, a potential gradient is set up. If the potential gradient is
above 30 kV/cm, the conductor gets ionized. The phenomenon of faint violet glow, hissing noise and
production of ozone gas is known as corona.
11. Define proximity effect on conductor? (May 2015)
The alternating magnetic flux in a conductor caused by the current flowing in a neighboring
conductor gives rise to circulating currents which cause non-uniformity of current and an
apparent increase in the resistance of the conductor. This phenomenon is known as proximity
effect.
12. Define the term critical disruptive voltage?(Dec 2011, Dec 2013)
The potential difference between conductors, at which the electric field intensity at the surface of the
conductor exceeds the critical value and occurs corona is known as critical disruptive voltage.
13. What are the factors affects the corona?
The factors affecting the corona are;
 Atmosphere.
 Conductor size
 Spacing between the conductors.
 Line voltage

14. Define visual critical voltage ?( Dec 2009, May 2013)
Minimum phase to neutral voltage at which corna glow appears and visible all along the conductors
is called visual critical voltage.
15. What are the factors depend upon the skin effect?
The skin effect depends upon the following factors;

 Nature of material.
 Resistivity.
 Frequency.

21.  Conductor size.
. PART B
1. Draw and explain the structure of electric power system indicating the voltage level in each
transmission levels. MAY/JUNE 2011,12,13,14,16, NOV/DEC 2013, 2007
2. Explain the following with respect to corona (i) corona (ii) effects of corona (iii) disruptive critical
voltage (iv) visual critical voltage (v) corona power loss (vi) interference with neighboring
communication circuits (vii) advantages, disadvantages and methods to reduce the effect of corona.
APRIL/MAY 2015 (R13, R8), NOV/DEC 2012, 13,16, MAY/JUNE 2013
3. Derive the capacitance of a single phase and three-phase overhead line for symmetrical spacing.
MAY/JUNE 2013, 14 (R8)
4. Deduce an expression for capacitance of three phase transmission line with unsymmetrical
spacing. (Transposed conductors) NOV/DEC 2012, 13,14,15, MAY/JUNE 2016
5. Starting from fundamental derivation of flux linkages with conductor per phase (derivation for
loop inductance of a single phase system), Derive the expression for the inductance per phase for a
3-phase overhead transmission system when conductors are symmetrically placed. APRIL/MAY
2015 (R8), DEC -2015, 13.
6. Derive an expression for the inductance per phase for a 3-phase overhead transmission system
with unsymmetrical spacing. MAY-13, NOV/DEC 2016
7. Derive an expression for the inductance per phase for a 3-phase overhead transmission system
with unsymmetrical spacing with transposed conductors
8. A three phase circuit line consists of 7/4.5 mm hard drawn copper conductors. The arrangement of
the conductors shown in Fig. The line is completely transposed. Calculate inductive reactance per
phase per km of the system. APRIL/MAY 2015 (R13), NOV/DEC 2011,13 (R8), MAY/JUNE
2016
9.
If the double circuit 3-phase line in Fig. has conductors of diameter 2.5 cm and distance of separation
(D) is 2m in the hexagonal spacing arrangement, calculate the phase-to-neutral capacitance in μF per
100km of the line. APRIL/MAY 2015 (R8)

22. 10. A 3-phase 80km long transmission line has its conductor of 1.0 cm diameter spaced at the corners
of the equatorial triangle of 100 cm side. Find the inductance per phase of the system. APRIL/MAY
2015 (R8)
11. Estimate the corona loss for a three-phase, 110Kv, 50Hz, 150Km long transmission line
consisting of three conductors each of 10 mm diameter and spaced 2.5m apart in a equatorial triangle
formation. The temperature of air is 300 𝐶and the atmospheric pressure is 750mm of mercury.
Assume the irregularity factor as 0.85. Ionization of air may be assumed to take place at a maximum
voltage gradient of 30Kv/cm. MAY/JUNE 2014 (R8)
12. Determine the capacitance/ phase of the double circuit line as shown in the fig. the diameter is
2.1793cm.

23. UNIT II MODELLING AND PERFORMANCE OF TRANSMISSION LINES
PART A
1. How are transmission lines classified ?[Nov 2017]
Based on the line length and voltage, the overhead transmission lines are classified as
Short transmission lines (length > 80km , voltage >20kV)
Medium transmission line (length <80km and > 200km, voltage<20kV and >100kV)
Long transmission line(length <200km , voltage <100kV)
2. How are transmission lines classified ?[Nov 2017]
Based on the line length and voltage, the overhead transmission lines are classified as
Short transmission lines (length > 80km , voltage >20kV)
Medium transmission line (length <80km and > 200km, voltage<20kV and >100kV)
Long transmission line(length <200km , voltage <100kV)
3. What is Ferranti effect? [Nov 2017] [May 2017][May 2015]
Define Ferranti effect? [May 2016]
In long transmission lines,receivingend voltage is greater than sending end voltage during light
load or no-load operation. Under no load or light, the capacitance associated with the line
generate more reactive power than the reactive power which is absorbed, hence VR > VS. This
effect is known as Ferranti effect.
4. Write down the significance of SIL on transmission line. [May 2017]
Mention the significance of surge impedance loading. [May 2016]
The surge impedance loading of a line is defined as the power delivered by a line to a pure
resistive load equal to its surge impedance.
SIL is also called as natural power of the line

24. The permissible loading of a transmission line can be expressed as a fraction of its SIL and
provides a comparison of load carrying capabilities of lines
5. State the condition for maximum power delivered and draw the power angle diagram.
[Nov 2016]
The maximum power delivered when power angle ∂=90 degree
6. Mention the various methods of voltage control transmission lines. [Nov 2016] NOV/DEC
2011 (R8)
Voltage control of transmission lines can achieved following methods
Use of series capacitors
Use of shunt capacitors
Use of static VAR sources
Use of shunt reactors
Tap changing transformer
7. Define transmission efficiency. [Nov 2015]
The transmission line efficiency is defined as the ratio of power at the receiving end to the power at
sending end.
% transmission efficiency = ( PR) / (PS ) *100
Where PS – Sending end voltage
PR – Receiving End Voltage
8. Write the formula for finding surge impedance of transmission line. [Nov 2015]
Zc = √Z/Y = √L/C is pure resistance.
PR = |VRL|2/Zc
Where VRL = Line voltage at the receiving end.
Zc = Surge impedance = √L/C.
PR = Surge impedance loading.
9. What is the importance of voltage control.[May2015]
The voltage variation from generation station to consumer end are undesirable and suppliers are
required to maintain the voltage at prescribed limit so that voltage control are important in
transmission lines
10. Define voltage regulation in connection with transmission line. MAY/JUNE 2014,
NOV/DEC 2013, 2012.
Regulation of a transmission line is defined as the change in voltage at the receiving end,from no
load to full load, the sending end voltage remaining the same.
Mathematically it can be expressed as,
% Regulation = (VS – VR) / VR *100
Where VS – Sending end voltage
VR – Receiving End Voltage
11. How the capacitance effects are taken into account in a long transmission line?

25. Long transmission lines have length > 250km and operate at voltage higher than 100 kV the effects
of capacitance cannot be neglected. Therefore in order to obtain reasonable accuracy in long
transmission line calculations, the capacitance effects must be taken into account.
12. Define attenuation constant. NOV/DEC 2011
The real part of the propagation constant is α. It determines the change in magnitude per unit length
of the line of the wave is termed as attenuation constant. It is expressed in nepers per unit length
13. Define propagation constant. NOV/DEC 2011
The magnitude and the phase of a travelling wave is governed by the complex quantity γ. In other
wards γ governs the propagation of component wave.
Propagation constant γ = √ZY = α+jβ
Where α = Attenuation Constant
β = Phase Constant.
14. What is the use of power circle diagram?
The use of power circle diagram is to determine the maximum power that can be transmitted over the
line both at the receiving and the sending end.
15. What are the main objectives ofcompensation?
The main objectives of compensation are
To improve the system stability.
To produce substantially flat voltage profile.
To meet economically way for reactive power requirement.
To increase power transfer capability.
16. What are the devices used for compensation of transmission lines?
The devices used for compensation of transmission lines are
Shunt reactor.
Shunt capacitor.
Static VAR system.
Synchronous condensers.
Series capacitors
. 17. What is shunt compensation?
Shunt reactors are used to compensate for the undesirable voltage effects associated with line
capacitance. The amount of reactor compensation required to maintain the receiving end voltage at
the specified value.
PART B
1. A balanced three phase load of 30Mw is supplied at 132kV, 50 Hz and 0.85 p.f. lagging by means
of transmission line. The series impedance of a single conductor is (20+j52) Ω and the total phase
neutral admittance is 315 x 10−6 𝑆𝑖𝑒𝑚 . Using nominal T method, Determine (i) A, B, C and D
constants of the line (ii) sending end voltage (iii) regulation of the line. APRIL/MAY 2015 (R13)
2. Explain the real and reactive power flow in lines. Also explain the methods of voltage control.
APRIL/MAY 2015 (R13), NOV/DEC 2011, 2015,16

26. 3. (i) Explain the classification of transmission lines with their characteristics. (6m) NOV/DEC 2014
(R8)
(ii) Define the following:
(1) Surge impedance
(2) Attenuation constant
(3) Voltage regulation
(4) Transmission efficiency
(5) Concept of surge impedance loading. NOV/DEC 2012,13 (R8)
4. Perform the analysis of long transmission line using RIGOROUS method. NOV/DEC 2012 (R8)
5. What is power circle diagram? Explain the method of drawing sending end and receiving end
power circle diagram MAY/JUNE 2014 (R8), APRIL/MAY 2015 (R8)
6. Draw the nominal T circuit of a medium length transmission line and derive expressions for
sending end voltage and current. Also draw the respective phasor diagram. NOV/DEC 2015
7. Draw the nominal π and end condenser circuit of a medium length transmission line and derive
expressions for sending end voltage and current. Also draw the respective phasor diagram.
MAY/JUNE 2013
8. A 3-phase, 50Hz power transmission line has line resistance of 30 Ω and inductive resistance of 70
Ω per phase. The capacitive susceptance is 4 x 10−4 mho per phase. If the load at receiving end is 50
MW at 0.8 pf lagging with 132kV line voltage, calculate (i) sending end voltage and current (ii)
regulation and (iii) efficiency (iv) p.f. of the line for this load. Use nominal π method. APRIL/MAY
2015 (R8), NOV/DEC 2016, MAY/JUNE 2012
9. A 50Hz, three-phase transmission line is 250Km long. It has a total series impedance of (40+j100)
ohms and a shunt admittance of 914 x 10−6 ohms. It delivers 50MW at 220KV with a power factor
of 0.9 lag. Find the :
(i) Sending end voltage and current
(ii) Sending end power factor
(iii) Voltage regulation
(iii) Transmission efficiency by nominal-T method. MAY/JUNE 2014 ,16
10. The constants of three phase line are A=0.91 and B= 140 ohms/ phase. The line delivers 60 MVA
at 132kV and 0.8 pf lagging. Draw power circle diagrams and find (a) sending eng voltage and
power angle (b) the max power which the line can deliver with the above values of sending and
receiving end voltages (c) sending end power and pf (d) line losses MAY/JUNE 2016
11. A balanced 3 phase load of 30MW is supplied at 132 kV, 50 Hz and 0.85 P.F lagging by means
of transmission line. The series impedance of a single conductor is (20+j52) ohms and the total
phase-neutral admittance is 315 x 10−6 mho. Using nominal –T method , determine:
(i) The A, B, C and D constants of the line.
(ii) Sending end voltage.
(iii) Regulation of the line. NOV/DEC 2011 (R8)
12. A three phase, 50Hz transmission line, 40km long delivers 36 MW at 0.8 power factor lagging at
60KV (phase). The line constants per conductor are R = 2.5 Ω, L = 0.1 H, C = 0.25 μF. Shunt
leakage may be neglected. Determine the voltage, current, power factor, active power and reactive

27. voltamperes at the sending end. Also determine the efficiency and regulation of the line using
nominal π mehod. NOV/DEC 2013(R8)
13. A 15km long 3 phase overhead line delivers 5MW at 11 kv at 0.8 lagging p.f. line loss is 12% of
power delivered. Line inductance is 1.1 mH/km/phase. Find the sending end voltage and regulation.
DEC-2012
UNIT III MECHANICAL DESIGN OF LINES
PART A
1. What are the desirable properties of insulators? [Nov 2017]
The properties of an insulator are;
It should be mechanically strong to bear the conductor load.
It should have high dielectric strength.
High ratio of puncture strength to flash over voltage.
It should be non-porous.
It should not affected by the changes in the temperature.
2. Specify the different types of insulator? [may 2017]
The different types of insulators used for overhead lines are;
Pin type insulators.
Suspension type insulators.
Strain type insulators.
Shackle insulators.
Stay insulators.
3. What are the methods of improving string efficiency in line insulators? [nov 2016]
The methods for improving string efficiency are;
By reducing the value of K
By grading of insulators.
By using guard ring or static shielding.

4. What are the tests performed on the insulators? [May 2016]
The following tests are performed on insulators: 
1. Mechanical tests
2. Electrical insulation tests
3. Environmental tests
4. Temporary cycle tests
5. Corona and radio interference tests
5. Define string efficiency. [nov 2015]
String efficiency is defined as the ratio of total voltage across the string to the product of number of
units and the voltage across the unit adjacent to the line conductor. 
Mathematically it can be expressed as,

28. String efficiency = Voltage across the string
--------------------------------------------------------
(Number of insulators) x (Voltage across the unit nearest
to the line conductor)
6. What is the purpose of insulator? [may2015]
Insulators are the elements which provide necessary insulation between line conductors and
supports and thus prevent any leakage current from conductors to earth.
7. What is meant by tower spotting? [nov 2015]
The art of locating structures of towers in a right way and selecting their type and height so as to
meet all the necessary electrical requirements is called tower spotting. The sag template is used for
tower spotting.
8. What is meant by sag template? [nov 2015]
For normal spans and for standard towers, the sag and the nature of the conductor curve are
calculated under expected load conditions and plotted on a thin stiff plastic sheet. Such a graph is
called sag template.
9. What are the materials mainly used in bus bars? [may2015]
The bus bars are either rigid type or strain type.
For rigid type bus bars, copper or aluminium bars are used. Such bars are used for low and
medium voltage levels.
For strain type bus bars mainly stranded aluminium (ACSR) conductors are used which are
supported by strain insulators. The strain type bus bars are used for high voltage levels.
PART B
1. What are various properties of insulators? Also briefly explain various types of insulators
(suspension type and pin type are important). Draw the schematic diagram. Compare their merits and
demerits. APRIL/MAY 2015 (R13), MAY/JUNE 2012, 14 (R8), NOV/DEC 2014,2016
2. Define string efficiency of suspension insulator string. List the methods to improve it.
APRIL/MAY 2015, NOV/DEC 2012, 15,16, MAY/JUNE 2013, 16
3. What is sag-template? Explain how this is useful for location of towers and stringing of power
conductors? Explain the factors affecting sag. NOV/DEC 2013 (R8), NOV/DEC 2014 (R8)
4. Deduce an approximate expression for sag in overhead lines when supports are approximated by a
parabola. How can the effect of wind and ice loading be taken into account? NOV/DEC 2013 (R8),
NOV/DEC 2015
5. Derive an expression for sag of a line supported between two supports of the different height.
NOV/DEC 2012 (R8)
6. Explain in detail about the types of towers.
7. A transmission line has a span of 275 m between level supports. The conductor has effective
diameter of 1.96 cm and weights 0.865 kg/m. Its ultimate strength is 8060 kg. If the conductor has
ice coating of radial thickness 1.27 cm and is subjected to a wind pressure of 39kg/𝑚2 of projected
area, calculate the maximum sag. Assume that the safety factor is 2 and ice weighs 910 kg/𝑚3
NOV/DEC 2014 (R8), MAY/JUNE 2016

29. 8. An overhead line has a span of 150m between level supports. The conductor has a cross sectional
area of 2 𝑐𝑚2. The ultimate strength is 5000 𝑘𝑔/𝑐𝑚2 and safety factor is 5. The
specific gravity of the material is 8.9 gm/cc. The wind pressure is 1.5 kg/m. calculate the height of
the conductor above the ground level at which it should be supported if a minimum clearance of 7 m
is to be left between the ground and the conductor. APRIL/MAY 2015 (R8)
9. A transmission line conductor at a river crossing is supported from two towers at a height of 50
and 80 meters above water level. The horizontal distance between the towers is 300 meters. If the
tension in the conductor is 2000 kg. Find the clearance between the conductor and water at a point
midway between the towers. Weight of conductor per meter = 0.844 kg. Derive the formula used.
NOV/DEC 2011,16, APRIL/MAY 2015 (R8)
UNIT IV UNDER GROUND CABLES
PART A
1. Mention any four materials used for underground cables. [Nov 2016]
Various insulating materials used in cable construction are Rubber, Paper & PVC.
2. Define grading of cables. (Dec 2004,Dec 2010, Dec 2012)
The process of achieving uniform electrostatic stress in the dielectric of the cables is called grading
of cables.
3. What is the main purpose of armouring ? (may2015)
It provides protection to the cable from mechanical injury. It consists of layers of galvanized steel
wires.
4. Give the relation for insulation resistance ofa cable.(Dec 2003,2006,2009, May 2013)
Insulation resistance of a single core cable is given by,
ρ
Rins = ------------ *ln(R/r) Ω
2 𝜋l
r =diameter of core
R =diameter of sheath
l =length of cable
5. What is dielectric stress?(May 2014 )
The insulation of a cable is subjected to electrostatic force under operating conditions is known as
dielectric stress.
6. Classify the cables used for three phase service. [may 2016]
Low tension (L.T) cables used up to 6.6 KV
Medium and high tension (H.T) cables up to 66 KV
The H.T. cables are further classified as :
Belted cables up to 11 KV
Screened cables for 22 and 33 KV
Pressure cables from 33 KV to 66 KV also called extra high tension cables

30. Super tension (S.T.) cables for 132 KV to 275 KV which are further classified as
Oil filled cables
Gas pressure cables
7. What is belted cables?[Nov 2017]
These types of cables used for the voltage levels up to 11kV. Here the cores are insulated from each
other by use of impregnated paper and grouped together with paper belt.
PART B
1. Define Grading of cables. Discuss the capacitance grading and intersheath grading of underground
cables. MAY/JUNE 2013,14,16 (R8), NOV/DEC 2012
2. Derive an expression for capacitance of a single core and three core cables. NOV/DEC 2013, 14
(R8)
3. Describe the general construction of an underground cable with a neat sketch. And also explain the
types of underground cables. APRIL/MAY 2015 (R8), NOV/DEC 2011, 12, 13 (R8)
4. (i) Explain any four insulating materials used in manufacturing of cables. NOV/DEC 2015
(ii) A string of eight suspension insulators is to be graded to obtain uniform distribution of voltage
across the string. If the capacitance of the top unit is 10 times the capacitance to ground of each unit,
determine the capacitance of the remaining seven units. NOV/DEC 2015
5. In a 3 unit insulator, the joint to tower capacitance is 20% of the capacitance of earth unit. By how
much should the capacitance of the lowest unit be increased to get a string efficiency of 90%? The
remaining two units are left unchanged. APRIL/MAY 2015 (R13)
6. Each line of a 3-phase system is suspended by a string of three identical insulators of self-
capacitance C farad. The shunt capacitance of connecting metal work of each insulator is 0.2 C to
earth and 0.1 C to line. Calculate the string efficiency of the system if a guard ring increases the
capacitance to the line of metal work of the lowest insulator to 0.3 C. NOV/DEC 2014 (R8),
APRIL/MAY 2015 (R8)
7. An insulating string for 66KV lines has 4discs. The shunt capacitance between each joint and
metal work is 10% of the capacitance of each disc. Find the voltage across the different disc and
string efficiency. NOV/DEC 2013 (R8)
8. A 3 phase overhead transmission line is being supported by three disc insulators. The potential
across top unit and middle unit are 9 kV and 11 kV respectively. Calculate (i) the ratio of capacitance
between pin and earth to the self-capacitance of each unit. (ii) The line voltage and (iii) string
efficiency. NOV/DEC 2011 (R8)
9. A three unit insulator string is fitted with a guard ring. The capacitance of the link pins to metal
work and guard ring can be assumed to be a 15% and 5 % of the capacitance of each unit. Determine
voltage distribution at each unit and string efficiency. MAY/JUNE 2013,16
10. A string of five insulator units has mutual capacitance equal to 10 times the pin to earth
capacitance. Find voltage distribution across various units as the percentage of the total voltage
across the string and string efficiency. NOV/DEC 2016
11. A 2km long 3 core cable has capacitance of 0.5mF/km between two conductors bunched with
sheath and the third conductor. The capacitance between the conductors is also measured when
bunched together and the sheath and found to be 0.75mF/km. Determine. (i) Capacitance between
phases. (ii) Capacitance between the conductor and the sheath (iii) Effective per phase Capacitance

31. (iv) Capacitance between two conductors connecting a third conductor to be sheath. (v) Charging
current if the supply voltage is 11kV, 50Hz. NOV/DEC 2016
12. An insulator string consists of three units, insulator nearest to the line having a safe working
voltage of 20kV. The ratio of self to shunt capacitance is 6:1. Find the line voltage and string
efficiency. MAY/JUNE 2012
UNIT V DISTRIBUTION SYSTEMS
PART A
1. List out the advantages of high voltage A.C. transmission. MAY/JUNE 2016, NOV/DEC 2011
(OR) Why is electrical power preferable to be transmitted at high voltage? (May 2015)
The volume of copper required is less at high voltage level
The efficiency is higher
Line drop becomes less
The power handling capacity of line increases
The total line cost per MW per km decreases
2. Define the terms feeders and Distributors. APRIL/MAY 2015, NOV/DEC 2012, 16, NOV/DEC
2011,12, (May 2015)
The feeders are the conductors which are of large current carrying capacity. The feeders connect
the substation to the area where power is to be finally distributed to the consumers
Distributors are the conductors used to transfer power from distribution centre to the consumers
3. What are the objectives of FACTS? (Dec 2017) MAY-2010
The power transfer capability of transmission system is to be increased
The power flow is to kept over the designated routes.
4. What is ring main system?(May 2017)
In this system the feeders covers the whole area of the supply in the ring fashion and finally
terminates at the substations from where it is started .the feeders is in closed loop form and looks like
a ring hence the name given to the system is ring main distribution system.
5. What is interconnected system?(Dec 2017)
When a ring main system is supplied by two or more than two generating stations then it is called
interconnected system.
6. State the application of HVDC transmission. (Dec 2016)
Long distance bulk power transmission, for connecting two different areas for exchange of power.
Power transmission through underground or submarine cables.
Connect D.C. transmission with A.C. distribution systems.
Control and stabilization of power flow in A.C. ties in an integrated power system.
7. What is meant by STATCOM? (May 2007 ,May 2008)
STATCOM is a static synchronous generator operated as a shunt-connected static VAR compensator
(SVC) whose capacitive or inductive output current can be controlled independently of the A.C.
system voltage.
8. List out various devices used in FACTS. (May 2006 Dec 2008)

32. Static VAR compensators (SVC).
Thyristor controlled series compensator.
Thyristor switched series capacitors and reactors (TCSC).
Static Condensers (STATCOM).
Unified power flow control (UPFC).
9. Give any three HVDC lines in India.(May 2004, Dec 2008)
Rihand – Delhi HVDC transmission system.
Talcher – kolar HVDC transmission system.
Chandrapur – Padghe HVDC transmission system.
10. What is service mains?(May 2005,Dec 2011)
Electrical power service is provided to a consumer from the distribution feeder through/at the service
main.
11. Explain the term regional grid?(Dec 2007)
The interconnected transmission system of a state or a region is called the grid of state or region.
State grids are interconnected with the help of tie lines and form the regional grid.
12. Mention the types of HVDC links .(Dec 2005, May 2013)
Monopolar HVDC
Bipolor HVDC
Homopolor HVDC
Back to back HVDC coupling
Multi terminal HVDC
13. Why transmission lines are 3 phase 3 wire while the distribution lines are 3 phase 4 wire
circuit?(Dec 2013)
The transmission is at very high voltage level and such a balanced 3 phase system does not
required neutral conductor.
For distribution it is necessary to supply single phase loads long with the three phase loads. For
single phase distribution a neutral conductor is must.
14. What are the major equipments of substation? [nov 2017]
The various substation equipments are;
Transformers.
Circuit breakers.
Isolators.
Load break switch.
Instrument transformers.
Current transformers.

33. Potential or Voltage transformers
Busbars
Protective relays
Lightning arresters or surge arresters.
Earthing switch.
Shunt capacitors.
Earthing
Station battery and charging equipment.
15. Enlist any two factors that affect the sag in transmission line. [may 2017] (or)
What are the factors that affect the sag in transmission line? [nov 2016]
The two important atmospheric factors affecting the sag in transmission line are,
Ice coating on the conductor which increases the weight of conductor.
Wind pressure due to which the conductor gets subjected to the additional forces
Apart from these two factors the span, weight of conductors and the tension in the conductor also
affect the value of sag.
16. Write down the types of grounding. [may 2017]
The types of grounding are
Solid or effective grounding
Resistance grounding
Reactance grounding
Resonant grounding
17. What is the need of earthing ? [nov 2016]
To ensure that live parts should not assume a potential which is dangerously different from that of
surroundings.
To allow sufficient current to flow safely for proper operation of protective devices like circuit
breakers, etc.


To suppress dangerous potential gradients.
18. Define sag. [may 2016]
When a conductor is suspended between two points then it takes the shape of parabola or
catenary and sags down.
The difference in levels between the point of support and the lowest point on the conductor
19. What is meant by string chart? [may 2016]
Give the significance of string chart? [nov 2017]
The tension at the time of erection of a transmission line is given by a cubic equation hence it is
time consuming to solve such equation.
Instead of solving such a equation the graph of tension in kg against the temperature in ⁰C and the
graph of sag in meters against the temperature in ⁰C is obtained.
Such graphs are called stringing chart.
20. What is substation?

34. Substations are the point in the power network where transmission lines and distribution feeders are
connected together through circuit breakers or switches namely busbars and transformers.
21. How will you select an ideal location for a distribution substation?
Distribution substations are connected between primary distribution and secondary distribution. The
primary distribution voltages such as 11kV or 6.6kV are to be stepped down to the supply voltage.
These substations transfer power to the consumers through distributors and service mains.
22. What is the role of circuit breaker in power system?
When a fault occurs in the bus bar the relay sense the fault and gives command signal to the circuit
breaker. The circuit breakers disconnect and isolate the faulty section thereby protecting the
equipments.
23. Write down the difference between disconnector switch and isolator.
Whenever maintenance or repair work is to be carried out on equipment in a substation, it is
disconnected from the supply by the isolators. It is operated under no load. Isolators are interlocked
with circuit breakers and earthing switches. To open isolators, circuit breakers are to be opened first.
24. What are the classifications of substation according to the service? [may2015]
According to service, the substations are classified as:
Transformer substations
These are further classified as
Transmission or primary substation
Sub transmission or secondary substation
Step down or distribution substation
Industrial substations
Switching substations
Synchronous substations
Frequency change substations
Converting substations

PART B
1. Discuss in detail about substation layout GIS and AIS. MAY/JUNE 2012
2. write short notes on :
(i) Sub mains
(ii) Stepped and tapered mains
(iii) Grounding grids APRIL/MAY 2015 (R13), NOV/DEC 2012 (R8)
3. Explain the following:
(i) Neutral grounding
(ii) Resistance grounding
(iii) Resonant grounding
(iv)Reactance earthing. APRIL/MAY 2015, MAY/JUNE 2013, 16, NOV/DEC 2015,16

35. 4. Discuss in detail the advantages and disadvantages and application of HVDC transmission.
APRIL/MAY 2015 (R13), NOV/DEC 2016
5. Explain with a neat layout the modern EHV system. What is the highest voltage level available in
India for EHV transmission? Also discuss the advantages of EHVAC. NOV/DEC 2012,13,
APRIL/MAY 2015 (R13)
6. Discuss in detail the problem associated with EHV AC transmission. State how these problems are
being solved. Also explain the effect of high voltage on volume of copper and on efficiency.
NOV/DEC 2013, 14, 16, MAY/JUNE 2012
7. What are the various types of HVDC links? Explain them in detail. NOV/DEC 2011,12,16,
MAY/JUNE 2008,10,13, 16
8. List out the adjectives of FACTS. What are the basic types of FACTS controllers? And explain
about FACTS controllers. NOV/DEC 2012,13, 14 (R8), MAY/JUNE 2010,12,16
9. Discuss the various FACTS devices. DEC 09, MAY-12, MAY/JUNE 2012
10. Explain the following system of distribution: APRIL/MAY 2015 (R13), 11, NOV/DEC
2010,12,13
(i) Radial system
(ii) Ring main distribution system/ Ring main distributor
(iii) Interconnected system
(iv) Design consideration in distribution system.
(v) Stepped (or) tapered distributor
(vi) DC distributor fed at one end
(vii) DC distributor fed at both ends.
(Question no. 9 covers also the explanation of types of AC and DC distributors)
11. (i) Derive suitable expressions, draw current loading diagram and voltage drop diagram for
uniformly loaded distributor of length ‘l’ fed at one end. How is power loss in the whole distributor
computed? NOV/DEC 2015,16
(ii) A uniform two wire DC distributor 250m long is loaded with 0.4 A/m and is fed at one end. If the
maximum permissible voltage drop is not to exceed 10V, find the cross sectional area of the
distributor conductor. Take ρ = 1.78*10-8 Ωm. NOV/DEC 2015
12. (i) Consider a distributor loaded with uniform loading of i ampere/m run and are fed from two
end feeding points at different voltages. Find the point of minimum potential occurrence in the
distributor. NOV/DEC 2015
(ii) A 800m long, two wire DC distributor fed from both ends, is loaded uniformly at the rate of
1.2A/m run. If the resistance of the distributor is 0.1 Ω/km (go and return) and feed points are
maintained at 245V and 240V respectively. Calculate the min voltage, its point of occurrence and
current supplied from two feeding points. NOV/DEC 2015
13. A two wire dc ring main distributor ABCDEA is fed at point A with 230V supply. The resistance
of go and return conductors of each section AB,BC,CD,DE,AE are 0.1 ohm. The main supplies the
loads of 10A at B, 20A at C, 10A at D, 30A at E. find the voltage at each load point. MAY/JUNE
2016