Construction EHV Transmission Line

Transmission of Power

Transmission Lines

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Introduction


What is Power Transmission ?

Power transmission is the movement of energy from its

place of generation to a location where it is applied to

performing useful work.

Electric power is normally generated at 11-33 kV in a power

station. To transmit over long distances, it is then stepped-

up to 400kV, 220kV or 110 kV as necessary.

Power is carried through a transmission network of high

voltage lines. Usually, these lines run into hundreds of

kilometers and deliver the power into a power grid.


What is Power Transmission ?

The grid is connected to load centres (cities) through a

sub-transmission network of normally 33kV (or

sometimes 66kV) lines.

These lines terminate into a 33kV (or 66kV) substation,

where the voltage is stepped-down to 11kV for power

distribution to load points through a distribution

network of lines at 11kV and lower.


Efficiency of transmission Line

Whatever may be the category of transmission line, the

main aim is to transmit power from one end to another.

Like other electrical system, the transmission network

also will have some power loss and voltage drop during

transmitting power from sending end to receiving end.

Hence, performance of transmission line can be

determined by its efficiency and voltage regulation.



Every transmission line will have three basic

electrical parameters.

The conductors of the line will have electrical

resistance, inductance, and capacitance.

As the transmission line is a set of conductors

being run from one place to another supported

by transmission towers, the parameters are

distributed uniformly along the line.

http://www.electrical4u.com/electrical-transmission-tower-types-and-design/





Power sent from sending end - line losses

=

Power delivered at receiving end.


The transmission lines are categorized as three types:

1) Short transmission Line – the line length is up to 80 km.

2) Medium Transmission Line – the line length is between

80km to 160 km.

3) Long Transmission Line – the line length is more than

160 km.

Transmission Lines

Extra High Voltage

110 kV, 132 kV, 220 kV, 400 kV

Ultra High Voltage

765kV

High Voltage Direct Current

±500kV

Transmission Line Execution

Survey

&

Profile Plotting

Transmission Line Survey

A transmission line is one of essential infrastructures of

the power supply system.

In the site evaluation process for those facilities, it is

necessary to carefully consider not only technical issues,

but also the impact on natural environment, the influence

on local communities, and various regulations.

To achieve optimum line length, minimise rocky and

water terrains, reduced tower angle cut points, ROW

issues etc; it is necessary to have detailed survey, profile

of transmission line route.

Transmission Line Survey

Why Surveying Is Important ?

To optimize cost of transmission line

Line length, number of locations, deviations.

Minimum river crossings.

Minimum forest areas.

Accessibility, right of way considerations.

To assess route constraints and do construction planning.

To ensure statutory clearances

Ground clearance.

Horizontal/Right of way clearance.

Clearances from power lines, railway lines, road crossings etc.

UHV Transmission Lines - 765 kV ,

Requiring Large ROW

Transmission Lines through Agricultural fields

Transmission Lines in Hilly areas

Transmission Line River Crossings

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http://192.168.1.18/PN/Gallery/view.asp?img=IMAGES/TOWERS/POWERGRID TOWERS/TALCHER-KOLAR/TMP28.JPG&folder=IMAGES/TOWERS/POWERGRID TOWERS/TALCHER-KOLAR&si=True&up=IMAGES/TOWERS/POWERGRID TOWERS

Multiple Transmission Lines

Through Same Corridor

Transmission Line Survey :

Project Conceptualization / Project Feasibility Stage:

Faster and accurate techniques required to evaluate

various line routes .

Pre-Construction Stage:

Route alignment, Detailed Mapping of right of way,

ground profiling, finalisation of tower locations.

Detailed contouring of undulated terrain for estimation

of benching and revetment quantities

Project Construction Stage

Check Survey only

Detailed Survey – Modern Techniques

Route Alignment using latest satellite imageries

superimposed on Survey of India Topographical Maps.

Digital terrain modeling in hills using contouring data.

Detailed Survey using GPS, Total stations or ALTM.

Digitized contouring at undulated / hilly tower locations.

Identification of Route constraints.

Identification of infrastructure details .

Tower spotting & optimization of locations using

commercial software like PLS CADD.

Estimation of BOQ & Preparation Of Survey reports.

Soil Investigation.


Global Positioning System

Total Station

PLS CADD

Detailed Survey – Modern Techniques Global Positioning System

The Global Positioning System

(GPS) is a space-based satellite

navigation system that provides

location and time information in

all weather, anywhere on or

near the Earth, where there is

an unobstructed line of sight

GPS satellite.

It is a modern technology that

improves survey engineering to

Global orientation.

Detailed Survey – Modern Techniques Total Station

A Total Station is a modern

surveying instrument that

integrates an electronic

theodolite with an electronic

distance meter.

A theodolite uses a movable

telescope to measure angles in

both the horizontal and vertical

planes.

Coordinates of an unknown point

relative to a known coordinate

can be determined using the

total station.


PLS CADD Power Line Systems –

Computer Aided Design and Drafting

PLS-CADD is the most powerful overhead power line

design program.

PLS-CADD is a sophisticated three-dimensional

engineering model.

The model can be viewed in a number of different

ways: profile views, plan views, plan & profile sheets,

3-D view etc.

PLS-CADD supports both automatic and manual

spotting.


PLS – CADD software - Some views

Transmission Line

Sample route Profile through Google Earth

Transmission Line

Sample route Profile

Topo Map

Sending end SS

Receiving end SS

AP 1

AP 2

AP 3

AP 4

Bee Line

Digitized Toposheet

Survey of India Topo Sheet Corresponding Digitized Map indicating relevant information

Computerized Route Optimization by Study of

Alternative Routes

Bee Line

Existing Line

Alternative

3

Alternative

2

Alternative 1

Digital Terrain Model –

Computerized Three Dimensional Image

Plan & Profile Drawing

Transmission Line Survey:

The detailed survey is taken up on the line route

approved by the concerned Electricity board.

Detailed survey should cover:

Fixing of Alignment

Fixing of Line Points

Fixing of Angles of deviation

Fixing of Angle Points

Fixing of Direction Points

Measuring of distance between Angle Points

Levels at every 10 M interval or where there is level

difference of 30 Cm


Detailed survey should include:

Details of Roads

Details of Villages

P & T Lines Crossings

All Power Lines Crossings – LT to 765 kV

Railway Crossings

River Crossings

Agricultural wells, Field bunds & Earth bunds etc.

Measuring Soil resistivity at 1 Km interval

Trial Pits

Crop & Tree enumeration


Detailed survey Obligatory Points

AVOID:

Reserve Forest Area

Military Firing Ranges

Aerodromes

Inhabited and thickly populated areas

Hilly terrain

Marshy, Low lying & Submersible areas

Higher & 90 degrees angle turnings

Oil & Gas storage areas

Transmission Line Profile:

Detailed Profile should be

From the details of route survey, route plan and ‘Profile’, is

prepared. Profile is also termed as Longitudinal profile or

route profile.

The profile is prepared and plotted paper rolls of graphed

tracing paper.

The profile shall progress from left to right.

A typical profile is enclosed.

Transmission Line Profile


Detailed Route Profile should be

Graphical representation

Preferably be in the Scale of

X-axis 1 Cm = 20 M

Y-axis 1 Cm = 2 M

Plot Plan of Alignment of Line from AP to AP

Plot Distances

Plot Levels with respect to distance


Detailed Profile should include & indicate

All Power Lines crossings: LT to 765 kV

All P & T Lines crossings

All Railway crossings

All River crossings

All Roads: Cart Tracks to National Highways

All Villages

All Agricultural wells

All Field bunds & Earth bunds

All Ponds & Lakes

Type of Soil

Crops & Trees

Transmission Line Profile


Tower Spotting

Identify the position of Terminal Tower.

Start from Terminal Tower.

Match the tower footing curve with the position of TT.

Adjust the position of template.

Ensure Ground Clearance.

Identify the position of next tower.

Move the template to the next tower.

Repeat the procedure.


Tower Spotting

NORMAL SPAN:

It is the design span

ACTUAL SPAN:

It is the actual distance between two adjacent towers

NULL POINT:

It is a point in a span where the position of the conductor is

lowest (or) It is a point in a span where the sag is maximum

WEIGHT SPAN:

The distance between two adjacent null points

WIND SPAN:

It is the distance between two centre points of adjacent spans.

Transmission Line Profile – SAG TEMPLATE

Transmission Line Profile – Span Limitations

SPAN 110 / 132 kV

220 kV 400 kV

NORMAL SPAN 320 M 350M 400 M

WIND SPAN

Both 320 M 350 M 400 M

Single 192 M 210 M 240 M

WEIGHT SPAN

Both 400 M 450 M 600/800 M

Single 240 M 270 M 300/400 M

Transmission Line Profile – Clearances

Details 110/

132 kV 220 kV 400 kV

Ground Clearance 6.1 M 8.5 M 9.0 M

LT to 132 kV and P& T Lines

3.1 M 4.6 M 5.5 M

220 kV 4.6 M 4.6 M 5.5 M

400 kV 5.5 M 5.5 M 5.5 M

Transmission Line Profile – Clearances

Details 110 /

132 kV 220 kV 400 kV

Highway Crossing 9 M 9 M 9M

Railway Crossing 14.6 M 15.4 M 17.9 M

Railway Crossing Span (Max)

2/3 of NS 2/3 of NS 2/3 of NS

Distance between Tower & Railway

Track (Min) TH+6 M TH+6 M TH+6 M

Transmission Line – Tower Schedule

Location No.

Type of

Tower

Angle of Deviation (degrees)

Span (M)

Left Wt.

Span (M)

Right Wt. Span (M)

Total Wt. Span (M)

Remarks

SS Boom - - - - Boom at sending

end SS

70

1 TT S 35 L - 75 - Terminal tower at

sending end SS

210

2 P - 135 150 285

300

3 R 22 R 150 130 280 Near village

280

4 P+3 - 150 125 255 33 kV Line crossing

250


Check Survey

Marking of Tower Location

Forward & Backward Line Points

Pit Marking

Excavation

Transmission Line

Foundation

Transmission Tower Foundation

Type of loads on foundation :

The foundation of towers are normally subjected to three

types of forces. These are:

a) The compression or downward thrust.

b) The tension or uplift.

c) The lateral forces of side thrusts in both transverse

and longitudinal directions.


Depending on the type of soil and the presence of surface

water table , four types of foundation will be used for each

type of tower location.

Normal dry type :

To be used for location in normal day cohesive or non-

cohesive soils.

Partially sub-merged type :

To be used at locations where sub soil water table is

met between 0.75 metre below the ground line.


Fully sub-merged type :

To be used at locations where sub-soil water table is met

at less than 0.75 metre below the ground line.

Wet type :

To used for locations:

1. Where sub-soil water is met at 1.5 m or more below

the ground line.

2. Which are in surface water for long periods with water

penetration not exceeding one metre below the ground

3. In black cotton soils.


In addition, depending on the site conditions, other types of

foundations may be introduced suitable for:

Intermediate conditions under the above classification to

effect more economy, or

- For locations in hilly and rocky areas.

- For locations where special foundations (well type or

piles) are necessitated.


Testing of soil

It is desirable to undertake testing of soil for all the tower

locations and report should be obtained about the sub-soil

water table, bearing capacity of soil, possibility of

submergence and other soil properties required for the correct

casting of casing of foundations.


Tower Foundation:

1. Excavation

2. PCC

3. Stub setting

4. Template Alignment

5. Concreting

6. Curing

7. De-shuttering & Template removal.

8. Back- Filling


Excavation


Excavated pit on hard rock


Water at Excavated pit Dewatering


Stub setting & Template Assembly


Base levelling with sand filling


PCC


Raft Concrete


Stub Concrete

Stub Footing concrete

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Tower Erection

Transmission Tower Erection

Method of Tower Erection

There are four main methods of erection of steel

transmission towers which are described below:

1) Build-up method or Piecemeal method.

2) Section method.

3) Ground assembly method.

4) Helicopter method.


Build Up Method of Tower Erection

This method is most commonly used in India for the erection

of 66kV, 132kV, 220kV and 400kV transmission line towers.

This method consists of erecting the towers, member by

member. The tower members are kept on ground serially

according to erection sequence to avoid search or time loss.

The erection progresses from the bottom upwards. The four

main corner leg members of the first section of the tower

are first erected and bolted with the stub.



The cross braces of the first section which are already

assembled on the ground are raised one by one as a unit

and bolted to the already erected corner leg angles.

The cross braces of the first section which are already

assembled on the ground are raised one by one as a unit

and bolted to the already erected corner leg angles.

The members / sections are hoisted either manually or by

winch machines operated from the ground.

After the tower top is placed and all side lacing are bolted

up. Cross – Arms are erected as complete unit .


Section Method of Transmission Tower Erection

In the section method, major sections of the tower are

assembled on the ground and the same are erected as units.

These Units are erected with the help of mobile cranes.

Ground Assembly Method of Tower Erection

This method consists of assembling the tower on ground, and

erecting it as a complete unit. The complete tower is

assembled in a horizontal position on even ground.

In India, this method is not generally adopted because of

prohibitive cost of mobile crane, and non-availability of good

approach roads to tower locations.


Helicopter Method

• In the helicopter method, the

transmission tower is erected in

section. Sometimes a completely

assembled tower is raised with

the help of helicopter.

• This method is mostly used

where access to the tower

location is limited.

1


Tower erection - Finishing Works

All nuts shall be tightened with one to two threads shall be

projected outside the nuts.

Punching after nut tightening and tack welding shall be

done along with bolt and nut together to ensure that the

nuts are not loosened in course of time.

The joints shall be painted with zinc paint on all contact

surfaces during the course of erection to avoid rusting.

The finally erected tower shall be truly vertical after

erection. Tolerance limit for vertical shall be one in 360 of

the tower height.


Tower Erection in progress

Electrical Transmission Tower types and design

The main supporting unit of overhead transmission

line is transmission tower.

Transmission towers have to carry the heavy

transmission conductor at a sufficient safe height

from ground. In addition to that all towers have to

sustain all kinds of natural calamities.

So transmission tower designing is an important

engineering job where all three basic engineering

concepts, civil, mechanical and electrical engineering

concepts are equally applicable.

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Tower Erection


A transmission tower consists of the following parts.

1) Peak of transmission tower

2) Cross arm of transmission tower

3) Boom of transmission tower

4) Cage of transmission tower

5) Transmission Tower Body

6) Leg of transmission tower

7) Stub/Anchor Bolt and Base plate assembly of

transmission tower.


Peak of Transmission Tower

The portion above the top cross

arm is called peak of

transmission tower. Generally

earth shield wire connected to

the tip of this peak.


Cage of Transmission Tower

The portion between tower body

and peak is known as cage of

transmission tower. This portion of

the tower holds the cross arms.


Cross Arms of Transmission Tower

The portion from bottom cross arms

up to the ground level is called

transmission tower body.

This portion of the tower plays a vital

role for maintaining required ground

clearance of the bottom conductor of

the transmission line.


Design of Transmission Tower

During Design of transmission tower the following points

to be considered in mind.

1. The minimum ground clearance of the lowest

conductor point above the ground level.

2. The length of the insulator string.

3. The minimum clearance to be maintained between

conductors & between conductor and tower.

4. The location of ground wire with respect to outer

most conductors.


Transmission Tower

To determine the actual transmission

tower height by considering the above

points, we have divided the total height of

tower in four parts.

1. Minimum permissible ground clearance

(H1).

2. Maximum sag of the conductor (H2).

3. Vertical spacing between top and

bottom conductors (H3).

4. Vertical clearance between ground

wire and top conductor (H4).


Types of Transmission Tower

According to different considerations, there are different

types of transmission towers.

The transmission line goes as per available corridors.

Due to unavailability of shortest distance straight

corridor transmission line has to deviate from its straight

way when obstruction comes.

In total length of a long transmission line there may be

several deviation points.



According to the angle of deviation there are four types

of transmission tower.

1) A – type tower – angle of deviation 0 to 2

2) B – type tower – angle of deviation 2 to 15

3) C – type tower – angle of deviation 15 to 30

4) D – type tower – angle of deviation 30 to 60



As per the force applied by the conductor on the cross

arms, the transmission towers can be categorized in

another way.

1. Tangent suspension tower and it is generally A - type

tower.

2. Angle tower or tension tower or sometime it is called

section tower. All B, C and D types of transmission

towers come under this category.



Apart from the above customized type of tower, the

tower is designed to meet special usages.

1. River crossing tower.

2. Railway/ Highway crossing tower.

3. Transposition tower.

These are called special type tower.


Classification of Transmission Tower

Based on numbers of circuits carried by a transmission

tower, it can be classified as:

1. Single circuit tower

2. Double circuit tower

3. Multi circuit tower.


Method of Tower Erection

There are four main methods of erection of steel

transmission towers which are described below:

1) Build-up method or Piecemeal method.

2) Section method.

3) Ground assembly method.

4) Helicopter method.



This method is most commonly used in India for the erection

of 66kV, 132kV, 220kV and 400kV transmission line towers.

This method consists of erecting the towers, member by

member. The tower members are kept on ground serially

according to erection sequence to avoid search or time loss.

The erection progresses from the bottom upwards. The four

main corner leg members of the first section of the tower

are first erected and bolted with the stub.

The members / sections are hoisted either manually or by

winch machines operated from the ground


Section Method of Transmission

Tower Erection

In the section method, major sections of the tower

are assembled on the ground and the same are

erected as units. Units are erected with the help of

mobile cranes.


Ground Assembly Method of Tower Erection

This method consists of assembling the tower on

ground, and erecting it as a complete unit. The

complete tower is assembled in a horizontal position

on even ground.

After the assembly is complete the tower is picked

up from the ground with the help of a crane and

carried to its location, and set on its foundation.


Helicopter Method

• In the helicopter method, the

transmission tower is erected in

section. Sometimes a completely

assembled tower is raised with

the help of helicopter.

• This method is mostly used

where access to the tower

location is limited.

1


Cross Arms assembled on ground for erection


Cross Arms Erected


Tower erection - Finishing Works

All nuts shall be tightened with one to two threads shall be

projected outside the nuts.

Punching after nut tightening and tack welding shall be

done along with bolt and nut together to ensure that the

nuts are not loosened in course of time.

The joints shall be painted with zinc paint on all contact

surfaces during the course of erection to avoid rusting.

The finally erected tower shall be truly vertical after

erection. Tolerance limit for vertical shall be one in 360 of

the tower height.

103/30

Stringing


Stringing

Stringing overhead conductors in transmission is a very

specialized type of construction requiring years of

experience, as well as equipment and tools that have

been designed, tried, and proven to do the work.


Medhods of installing

There are four methods that can be used to

install overhead transmission conductors:

Slack stringing

Semi-tension stringing

Full-tension stringing

Helicopter stringing


Slack stringing

This type is normally limited to lower voltage lines and

smaller conductors.

The conductors are normally placed on “Reels” or “Jack

Stand” and it is unreeled from the drum and dragged

along the ground by vehicle or pulling device.

This method is typically used during construction of

new lines where Right Of Way is readily accessible.


Semi Tension method of stringing

Semi tension methods are merely an upgrading of slack

stringing, but do not necessarily keep the conductor

completely clear of the ground, or the lines used to pull


Full Tension method of stringing

This is a method of installing the conductors in which

sufficient pulling capabilities on one end and tension

capabilities on the other, keep the wires clear of any

obstacles during the movement of the conductor from

the reel to its final sag position.

This ensures that these current-carrying cables are

“clipped” into the support clamps in the best possible

condition, which is the ultimate goal of the work itself.


Stringing with helicopters

This is much more expensive per hour of work, but can be much

less expensive when extremely arduous terrain exists along the

right-of-way and when proper pre-planning is utilized.

Although pulling conductors themselves with a helicopter can be

done, it is limited and normally not practical.

Maximum efficiency can be achieved when structures are set and

pilot lines are pulled with the helicopter, and then the conductor

stringing is done in a conventional manner.

Transmission Line

Component of Transmission Line

Transmission Line

Components of Transmission Line

Common Tools Required for Stringing

Material Handling - Conductors

Handling, Loading /Unloading ,Transport & Storage


Handling, Loading /Unloading ,Transport & Storage

1. Handling and transporting of the conductor and accessories shall

be carried out in such a manner as to minimize the possibility of

damages from abrasion through rough handling or dirt and grit.

2. The drums should always be transported in vertical position with

the cable ends fixed to prevent cable from slackening.

3. The drum should not be stored on its side under any

circumstances whatsoever.

4. The ends of the cable should be sealed to prevent water

penetration.

5. Loading and unloading are performed so that the drum remains

in vertical position and the sides of the drum are not damaged.


Avoid storage like this


Stringing Procedure

The stringing procedure is broadly divided into the following steps:

Paying out & stringing of Conductor.

Paying out & stringing of Earthwire.

Final sagging of Earthwire and conductor.

Clipping & Fixing accessories.


Steps of Stringing

Proper Guying

Insulator Hoisting.

Paying out of pilot wire & Conductor.

Rough sagging of conductor.

Final sagging of conductor.

Clipping & Spacering.

Finishing activities.

Jumpering.

Final Checking.

Guying Before commencing of stringing, the angle towers where the

stringing is to be started must be provided with guy supports.

Guying Precautions which should be taken at the time of guying?

The guys used generally are 20 mm steel wire rope. The guys are

attached to the tower at the tip of the cross arm , to the strain

plates with suitable D-shackles.

The guys are anchored in the ground at an angle of 45 deg. or

less from the horizontal, attached to dead end anchors .

The guy wire is attached to the dead end anchor wire with the

help of turn buckles of 10 tons capacity.

Excessive tightening of guy should be avoided. It is advisable to

tighten the guy progressively at the time of rough sagging of the

conductor.

Guying – Anchoring on ground

Insulator Hoisting

Insulator Hoisting Single / Double suspension insulator strings are used on

suspension towers and single /double tension insulator strings are

used on angle and dead end towers. This is generally indicated in

the tower schedule.

Double suspension insulator strings are used lines on Suspension

towers of Railway, River and Power Line Crossings only.

Suspension Type Insulators

Consist of a number of porcelain discs connected in series by metal links in the form of a string.

Suspension Type Insulators

The conductor is suspended at the

bottom end of this string while the

other end of the string is secured

to the cross-arm of the tower.

These insulators have a number of

interconnected porcelain discs,

with each unit designed to support

a particular voltage.

Together, a system of these discs is

capable of effectively supporting

high voltages.

Strain Type Insulators

When there is a dead end of the

line or there is corner or sharp

curve, the line is subjected to

greater tension. To relieve the line

of excessive tension, strain

insulators are used.

However, for the high voltage

transmission lines, strain insulator

consists of an assembly of

suspension insulators as shown.

Strain Type Insulators

Strain type insulators are

horizontally suspended suspension

insulators.

When the tension in lines is

exceedingly high, at long river

spans, power line, railway & road

crossings, two or more strings are

used in parallel.

Strain insulators are typically used

for high voltage transmissions.

Silicon Rubber Composite Insulators

Composite insulators with silicone

rubber sheds offer advantages over

traditional ceramics:

Improved safety for personnel

and equipment.

superior pollution performance

due to hydrophobic surface

condition.

Excellent seismic performance.

Low weight & Flexible design

Short delivery times

Insulator fitted with Roller and Pulley for conductor Payout

Insulator Prepared for Hoisting

Insulator Hoisting

Payout

The paying out of conductor is done generally between two

tension towers. In between two tension towers, there could

be either zero or one or more suspension towers.

A pilot wire is used to pull the conductor. The pilot wire is

initially laid through the centre wheel of the roller.

The pilot wire can be laid and joined with pilot wire

connectors or it can be pulled from one side of the section.

Scaffolding shall be provided for P&T and road crossing before

paying out of the pilot wire.

Stringing Procedure

Drum Scheduling - Basics

1. For effective utilization of the conductor and to prevent Wastage

of the conductor.

2. Details of Tower schedule, Receipt of drum details, Standard

length of each drum.

3. Knowledge of Usage of cut lengths for Jumpers and Short Spans.

4. All the joints or splices shall be made at least 30 metres away

from the tower structures.

5. No joints or splices shall be made in spans crossing over main

roads, railways and small river tension spans.

6. Not more than one joint per sub conductor per span shall be

allowed.

Transmission Line Tower Schedule

Transmission Line

Sample Drum Scheduling

Paying out Earthwire

Earthwire drum on turn table& unreeling in

progress for payout.

Payout of Earthwire

Final tensioning of Earthwire

Precautions before conductor Payout

Conductor Payout through Suspension Towers

Conductor Passing through rough terrains

Conductor Payout for each Phase

Conductor Rough Sag in progress

Conductor tensioning using come along Clamp and four sheave pulleys

Conductor Stringing Completed

Transmission Line Work Completion

Construction EHV Transmission Line

Engineering

Transcript of Construction EHV Transmission Line