Overhead Power Line: Profesor: Dr. Jovana Vilimonovic Student: Milan Vidovic Index Number: 3/2021

ACADEMY OF VOCATIONAL STUDIES
OF KOSOVO AND METOHIJA

DEPARTMENT OF ENERGY
Overhead power line
Profesor: dr. Jovana Vilimonovic

Student: Milan Vidovic
Index number: 3/2021
OVERHEAD
POWER LINE
History
■ The first transmission of electrical impulses over an extended distance was
demonstrated on July 14, 1729 by the physicist Stephen Gray
■ In 1912 the first 110 kV-overhead power line entered service followed by the
first 220 kV-overhead power line in 1923
■ In 1953, the first 345 kV line was put into service by American Electric
Power in the United States
■ In 1982 overhead power lines were built in Soviet Union between Elektrostal
and the power station at Ekibastuz
■ In 1999, in Japan the first powerline designed for 1000 kV with 2 circuits were
built, the Kita-Iwaki Powerline.
■ In 2003 the building of the highest overhead line commenced in China,
the Yangtze River Crossing
CONSTRUCTION
■ Towers for support of the lines are made of wood either grown or
laminated, steel or aluminum (either lattice structures or tubular
poles), concrete, and occasionally reinforced plastics
■ The bare wire conductors on the line are generally made of aluminum
(either plain or reinforced with steel or composite materials such as
carbon and glass fiber), though some copper wires are used in
medium-voltage distribution and low-voltage connections to customer
premises
■ Today overhead lines are routinely
operated at voltages exceeding 765,000
volts between conductors
Classification of transmission lines
BY OPERATING VOLTAGE:
Overhead power transmission lines are
classified in the electrical power industry by
the range of voltages:
■ Low voltage - less than 1000 volts
■ Medium voltage - between 1000 volts (1
kV) and 69 kV
■ High voltage - subtransmission or
transmission at voltages such as 115 kV
and 138 kV
■ Extra high voltage - from 345 kV up to
about 800 kV
■ Ultra high voltage is often associated
with ≥ ±800 kVDC and ≥ 1000 kVAC
BY LENGTH OF THE
LINE:
The overhead transmission line is generally categorized into three classes,
depending on the length of the line:
The transmission lines which have a length less than 50 km are generally referred
to as short transmission lines
The transmission line having its effective length more than 50 km but less than
150 km is generally referred to as a medium transmission line
A transmission line having a length more than 150 km is considered as a long
transmission line
Structures
■ Structures for overhead lines take a variety of shapes depending on the
type of line. Structures may be as simple as wood poles directly set in
the earth, carrying one or more cross-arm beams to support conductors,
or “armless” construction with conductors supported on insulators
attached to the side of the pole
■ Tubular steel poles are typically used in urban areas
■ High-voltage lines are often carried on lattice-type steel towers or
pylons
■ Poles made of reinforced plastics are also available, but their high cost
restricts application
■ Each structure must be designed for the loads imposed on it by the conductors
■ The weight of the conductor must be supported, as well as dynamic loads due
to wind and ice accumulation, and effects of vibration
■ Where conductors are in a straight line, towers need only resist the weight
since the tension in the conductors approximately balances with no resultant
force on the structure
■ Foundations for tower structures may be large and costly, particularly if the
ground conditions are poor, such as in wetlands
■ Lattice tower structures have two common
forms. One has a pyramidal base, then a
vertical section, where three crossarms
extend out, typically staggered
■ An optical ground wire is a more advanced
version with embedded optical fibers for
communication
■ Overhead wire markers can be mounted on Low-profile pover lines
near an airfield
the ground wire to meet International Civil
Aviation Organization recommendations.
Some markers include flashing lamps for
night-time warning
Main components of an overhead
power line:
- conductors
- ground wires
- towers
- insulation
- hardware
- foundations
Area under overhead power lines
■ Use of the area below an overhead line is limited because objects must
not come too close to the energized conductors.
■ Radio reception can be impaired under a power line, due both to
shielding of a receiver antenna by the overhead conductors, and by
partial discharge at insulators and sharp points of the conductors which
creates radio noise
■ In the area surrounding the overhead lines, it is dangerous to risk
interference, e.g. flying kites or balloons, using ladders, or operating
machinery
■ Overhead distribution and transmission lines near airfields are often
marked on maps, and the lines themselves marked with conspicuous
plastic reflectors, to warn pilots of the presence of conductor
Aviation accidents
■ General aviation, hang gliding,
paragliding, skydiving, balloon, and
kite flying must avoid accidental
contact with power lines
■ Nearly every kite product warns users
to stay away from power lines.
Deaths occur when aircraft crash into
power lines
■ Some power lines are marked with An aviation obstruction marker
obstruction makers, especially near on a high-voltage overhead
air strips or over waterways that may transmission line reminds pilots
support floatplane operations of the presence of an overhead
line. Some markers are lit at
night or have strobe lights
■ Electric power transmission line systems are
of great importance as structures
■ Transmission line systems relay the power
from production sites to the users
■ Failure of these structures can lead to power
cuts and therefore disrupt the day to day life
of people as well as the industries dependent
on electricity
THANK YOU FOR
YOUR ATTENTION!

Overhead Power Line: Profesor: Dr. Jovana Vilimonovic Student: Milan Vidovic Index Number: 3/2021

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ACADEMY OF VOCATIONAL STUDIES

OF KOSOVO AND METOHIJA

Overhead power line

Profesor: dr. Jovana Vilimonovic

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