Basic Terms

 Voltage

 Power – Real, Reactive & Apparent

 Power Factor

 Generator

 Transformer

 Transmission Line

 System Load

 Grid
OVERVIEW OF SYLLABUS
STRUCTURE OF POWER TRANSMISSION LINE
SYSTEM PARAMETERS

MODELLING AND
PERFORMANCE OF INSULATORS AND CABLES
TRANSMISSION LINES

MECHANICAL DESIGN OF
LINES AND GROUNDING
 UNIT 1

TRANSMISSION LINE PARAMETERS

 Structure of Power System.
 Parameters of single and three phase
transmission lines - 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 Electric Power
System
The Five Electrical Grids in
India
NRLDC

SRLDC
 Advantages of Higher
operating Voltage for AC

transmission
Reduces volume of conductor material
 Increases transmission efficiency

≈
By applying binomial
theorem
 Decreases percentage line drop

Limitations of high transmission

voltage
 the increased cost of insulating the conductors

 the increased cost of transformers, switchgear and other terminal

apparatus.
 EHV AC transmission
 Hydro-electric and coal or oil-fired stations are located very far from
load centers for various reasons which requires the transmission of the
generated electric power over very long distances.
 This requires very high voltages for transmission.

 The very rapid strides taken by development of dc transmission since

1950 is playing a major role in extra-long-distance transmission,
complementing or supplementing EHV AC transmission.
 HVDC transmission in
India
± 500 kV , 1500 MW Rihand – Dadri HVDC Project.

2 x 250 MW HVDC Vindhyachal Back to Back Station.

2 x 500 MW HVDC Chandrapur Back to Back Station.

+ 500 kV ,2000 MW, HVDC Talchar – Kolar Transmission Link.

1 x 500 MW HVDC Sasaram Back to Back Station.

2 x 500 MW HVDC Gazuwaka Back to Back Station.

+ 500 kV, 2500 MW HVDC Ballia – Bhiwadi Transmission Link.

 FACTS
FACTS:
“Alternating current transmission systems incorporating
power electronic-based and other static controllers to
enhance controllability and increase power transfer
capability.”

FACTS Controller:
“A power electronic-based system and other static
equipment that provide control of one or more A C
transmission system parameters.”
 Shunt Connected Controllers

 Static Synchronous Compensator (STATCOM)

 Static Var Compensator (SVC)

 Thyristor Controlled Reactor (TCR)

 Thyristor Switched Reactor (TSR)

 Thyristor Switched Capacitor (TSC)

 Static Var Compensator
(SVC)
“A shunt-connected static var generator or
absorber whose output is adjusted to exchange
capacitive or inductive current so as to maintain
or control specific parameters of the electrical
power system (typically bus voltage)”

A general term for a thyristor-controlled or thyristor-switched

reactor, and/or thyristor-switched capacitor or combination.
Schematic of SVC
 Thyristor Controlled Reactor (TCR):
A shunt-connected, thyristor-controlled inductor whose
effective reactance is varied in a continuous manner by
partial-conduction control of the thyristor valve.

 ThyrlstorSwltchedReactor(TSR): A
shunt-connected thyristor-switched inductor whose
effective reactance is varied in a stepwise manner by full-
or zero-conduction operation of the thyristor valve.
 Thyristor Switched Capacitor (TSC): A
shunt-connected, thyristor-switched capacitor whose
effective reactance is varied in a stepwise manner by
full- or zero-conduction operation of the thyristor valve.
 Static Synchronous Compensator
(STATCOM): A Static synchronous generator
operated as a shunt-connected static var compensator
whose capacitive or inductive output current can be
controlled independent of the ac system voltage.
Schematic of STATCOM
 Shunt Connected Controllers

 Static Synchronous Series Compensator (SSSC)

 Interline Power Flow Controller (IPFC)

 Thyristor Controlled Series Capacitor (TCSC)

 Thyristor-Switched Series Capacitor (TSSC)

 Static Synchronous Series
Compensator (SSSC): A static synchronous
generator operated without an external electric
energy source as a series compensator whose output
voltage is in quadrature with, and controllable
independently of, the line current for the purpose of
increasing or decreasing the overall reactive voltage
drop across the line and thereby controlling the
transmitted electric power.
 Combined Shunt and series Connected
Controllers
• UnifiedPowerFlow Controller (UPFC)

• Thyristor-Controlled Phase Shifting Transformer

(TCPST)
• Interphase Power Controller (IPC)
 MECHANICAL DESIGN OF
TRANSMISSION LINE BETWEEN TOWERS

 The successful operation of an overhead line

depends to a great extent upon the mechanical
design of the line
 An overhead line is subjected to uncertain weather
conditions and other external interferences
 mechanical strength of the line is such so as to
provide against the most probable weather
conditions
 MAIN COMPONENTS OF OVERHEAD
LINES
 Conductors which carry electric power from the
sending end station to the receiving end station.
 Supports which may be poles or towers and keep
the conductors at a suitable level above the ground.
 Insulators which are attached to supports and
insulate the conductors from the ground.
 Cross arms which provide support to the insulators.

 Miscellaneous items such as phase plates, danger

plates, lightning arrestors, anti-climbing wires etc.
 CONDUCTOR MATERIALS

Properties of conductor material:

 High electrical conductivity.

 High tensile strength in order to withstand

mechanical stresses.
 Low cost so that it can be used for long
distances.
 Low specific gravity so that weight per unit
volume is small.
 STRANDED CONDUCTORS

For n layers, the total number of individual wires is 3n(n + 1) + 1

Commonly used conductor materials:

 Copper

 Aluminium

 Steel-cored aluminium

 Galvanized steel

 Cadmium copper
Line Supports:
 Supporting structures for overhead line conductors
are various types of poles and towers called line
supports.
 Properties of line supports are,

– High mechanical strength to withstand the weight

of conductors and wind loads etc.
– Light in weight without the loss of mechanical
strength.
– Cheap in cost and economical to maintain.

– Longer life.

– Easy accessibility of conductors for maintenance.

 VARIOUS TYPES OF LINE SUPPORTS

 Wooden poles

 Steel poles

 R.C.C. Poles

 Lattice steel towers.

 INSULATORS
 provide necessary insulation between line
conductors and supports
 Prevent leakage current from conductors to earth
 Properties:
 High mechanical strength in order to withstand conductor load, wind load etc.

 High electrical resistance of insulator material in order to avoid leakage currents to

earth.
 High relative permittivity of insulator material in order that dielectric strength is high.

 The insulator material should be non-porous, free from impurities and cracks otherwise
the permittivity will be lowered.
 High ratio of puncture strength to flashover
 Types of Insulators

Pin type insulators

voltages upto 33 kV
Suspension type insulators
Strain insulators
Shackle insulators
 SAG IN OVERHEAD LINES
“The difference in level between points
of supports and the lowest point on
the conductor”
 Calculation of Sag
When supports are at equal levels

l = Length of span Two Forces:

w = Weight per unit length of The weight wx of
conductor conductor acting at a
T = Tension in the conductor distance x/2 from O.
The tension T acting at O.
Equating the moments of above two forces about point O,
When supports are at equal levels

l = Span length
h = Difference in levels between two supports
x1 = Distance of support at lower level (i.e., A) from O
x2 = Distance of support at higher level (i.e. B) from O
T = Tension in the conductor
Also, x1 + x2 1

=l

2
 Effect of wind and ice loading

Total weight of conductor per unit length is

 When the conductor has wind and ice loading also,
the following points may be noted :

The conductor sets itself in a plane at an angle θ to the

vertical where,

The sag in the conductor is given by ,

The vertical sag = S cos θ

 NUMERICAL PROBLEMS
1. An overhead line has a span of 260 m, the weight of
the line conductor is 0·68 kg per meter run. Calculate
the maximum sag in the line. The maximum allowable
tension in the line is 1550 kg. Ans: 3·7 m`

2. A 132 kV transmission line has the following data :

Wt. of conductor = 680 kg/km ; Length of span =

260 m

Ultimate strength = 3100 kg ; Safety factor = 2

Calculate the height above ground at which the
conductor should be supported. Ground clearance
3. A transmission line conductor is supported from two
towers at heights of 70m above water level. The horizontal
distance between the towers is 300 m. If the tension in the
conductors is 1500 kg, find the clearance at a point mid-
way between the towers. The size of the conductor is 0·9
cm2 and density of conductor material is 8·9 gm/cm3.
Ans: 64 m

4. A transmission line has a span of 150 m between level

supports. The conductor has a cross-sectional area of 2
cm2. The tension in the conductor is 2000 kg. If the specific
gravity of the conductor material is 9·9 gm/cm3 and wind
pressure is 1·5 kg/m length, calculate the sag. What is the
vertical sag? Ans: S=3·48 m ; Vertical Sag=2·77 m