transmission lines- presentation

8/22/2019 Transmission Lines- Presentation

1/24

SUMBUL.H.ABIDI

ELECTRICAL DEPARTMENT

S.P.C.E.

TRANSMISSION LINE


2/24

Earth

Wire.

Line

Insulator

Line

support

Conductor

Main comp-

Onents of

Over headline

Earth

Wire.

Line

Insulator

Line

support

Conductor

Main comp-

Onents of

Over headline

COMPONENTS OF OVER HEAD

LINE:-


3/24

The line supports are poles and the chief requirements for such supports are :

i ) They must be mechanically strong with factor of safety of 2.5 to 3 .

ii ) They must be light in weight without the loss of strength .

iii ) They must have least number of parts .

iv ) They must be cheap .

v ) Their maintenance cost should be minimum .vi ) They must be easily accessible for point and erection of line conductors .

vii ) They must have longer life .

viii ) They must be of pleasing shape


4/24

The different types of poles which can be used as line supports are :

a. Wooden poles .b. Steel tubular polesc. Reinforced concrete poles .d. Steel towers .

Fig.(1):Single phase single-circuit


5/24

Spacing between the

conduc tors

The most suitable spacing between theconductors can be arrived at bymathematical calculations.

It can only be obtained by empiricalformulae which have been obtained from

practical considerations.

Fig: Three-phase single circuit horizontal disposition ofconductor and steel towers


6/24

Generally the following formulae are used for obtainingspacing between the conductors :

Spacing=150

VS

Where,

S=sag in meters

V=voltage in KV


7/24

Span

SagInsulator

Tension Tower

Supporting

Tower Tension Tower

Transmission Line


8/24

Wooden PolesCheapest

Use for lines where span is short and tension is low.

Pole has limitation of height and diameter.Wood has natural insulating property and lesser flashover

takes place due to lightning.

For greater strength double pole structure of A or H are

used.

Concrete PolesConcrete poles are reinforced to give greater strength.

It has longer life span than that of wood

The maintenance cost is less.

They are heavy and are likely to get damage

duringloading,unloading,transportation and erection due totheir brittle nature.

Nowadays pre-stressed concrete supports are

manufactured in pieces.


9/24

Steel polesTubular steel poles or girder steel masts is favored for low and medium

distribution voltages.Longer span is possible.

Poles need to be galvanized or painted periodically to prevent corrosion.

Maintenance is expensive.

Steel TowersLines of 66 KV are supported on towers.

They fabricated from painted or galvanized angle section which are

transported separately and erection done on site.

Long life and high degree of reliability

They can withstand severe weather conditions.

The height of the towers depend on operating voltage and span length.The leg of the tower are set on concrete foundation


10/24

Types of steel towers

1. Tangent towers They are used for straight runs. Stress is due to weight of line,wind and ice load.

Extra forces due to break in the line on one side.

Base is either square or rectangle.

Suspension type insulators used.

2. Deviation tower They are used where transmission line changes

direction.

They have broader base , stronger members and

are costlier Strain insulators are used.

They are classified

i. Small angle towers(2o-15ochange in direction)

ii. Medium angle towers(15o-30ochange in

direction)

iii. Large angle towers(30o-60ochange in direction)


11/24


12/24

Transmission line (Steel tower)


13/24

Transmission line (Steel tower)


14/24

Lattice Towers


15/24

TYPES OF INSULATORS USED IN

OVERHEAD SYSTEM.

Pin type insulator.

Suspension type insulator.

Strain type insulator.

Shackle type insulator.


16/24

PIN INSULATORS

The pin type insulator is secured to the cross-arm on the pole. There is

a groove on the upper end of the insulator for housing the conductor.

The conductor passes through this groove and is bound by the

annealed wire of the same material as the conductor.

Pin type insulators are used for transmission and distribution of electric

power at voltages up to 33 kV. Beyond operating voltage of 33 kV, the

pin type insulators become too bulky and hence uneconomical.


17/24

Causes of failuresInsulators are required to withstand both mechanical and

electrical stresses.

The electrical stress is primarily due to line voltage and

may cause the breakdown of the insulator. The electrical breakdown of the insulator can occur either

by flash overorpuncture.

In flashover, an arc occurs between the line conductor and

insulator pin (i.e., earth) and the discharge jumps across

the air gaps, following shortest distance. Figure shows the

arcing distance (i.e. a + b + c) for the insulator.In case of flash-over, the insulator will continue to act in its

proper capacity unless extreme heat produced by the arc

destroys the insulator.

In case of puncture, the discharge occurs from conductor

to pin through the body of the insulator. When such

breakdown is involved, the insulator is permanentlydestroyed due to excessive heat. In practice, sufficient

thickness of porcelain is provided in the insulator to avoid

puncture by the line voltage.

The ratio of puncture strength to flashover voltage is

known as safety factor.


18/24


19/24

Locking KeyInsulator's Head

Expansion LayerImbedded Sand

SkirtPetticoats

Iron CapBall Socket

CompressionLoading

CementInsulating Glassor Porcelain

BallCorrosion Sleevefor DC Insulators

Steel Pin

Ball and socket type suspension insulator


20/24

Line Voltage

Number of Insulators per

String

69 kV 46

115 kV 79

138 kV 810

230 kV 12

345 kV 18

500 kV 24

765 kV 3035


21/24

ADVANTAGES

Each unit is designed for operating voltage of about 11KV .

The string is free to swing in any direction.It is designed for longer span and higher mechanical loading.

There is decreased liability to lightning disturbance if the

string is suspended from a metallic structure, which work as

lightning shield.

DISADVANTAGES

Spacing between conductor is increased

Height of tower increases

Cost is high.


22/24

Strain or Tension InsulatorStrain or tension insulators are designed for handling mechanical stresses at angle

positions where there is a change in the direction of the line at termination of line.

Suspension insulator are arranged in a horizontal position. They are used to handle

mechanical stresses and take the pressure off a conductor at the end of atransmission line, at a sharp corner or curve or over long river crossings.

Strain insulators are typically used for higher voltage transmissions.

Shackle Type Insulators

Shackle type insulators, similar to strain type insulators, are used on sharp curves,

end poles and in section poles.

However, unlike strain insulators, shackle insulators are designed to support lower

voltages. These insulators are single, round porcelain parts that are mounted

horizontally or vertically.


23/24

V-Strings

A single string of insulator follows the conductor and sways like a pendulum in a

strong side wind.V-strings are used to prevent conductor movement at towers. They are used for high

voltage transmission system.

INSULATOR MATERIAL1. Porcelain with glazed surface

2. Toughened glass

3. Polymer Insulator

Lattice Guyed tower


24/24

transmission lines- presentation

Documents