TO DESIGN PLAN ERECTION OF A HIGH

TENSION LONG TRANSMISSION LINE

ELECTRICAL DEPARTMENT

IDEAL INSTITUTE OF ENGINEERING

Presented By:Pritam Debnath

Introduction

The term high voltage characterizes

electrical circuits in which the voltage used

is the cause of particular safety concerns &

insulation requirements. High voltage is

used in electrical power distribution, in

cathode ray tubes, to generate x-rays &

particle beams, to demonstrate arcing, for

ignition, in photomultiplier tubes & high

power amplifier vacuum tubes & other

industrial & scientific applications .

Types of Transmission Line

There are two types of Long Transmission line.

1)Extra High Voltage (EHV)

2)Ultra High Voltage (UHV)

We will discuss about the EHV type only.

WHAT IS EHV TRANSMISSION ?

Two factors considered in the classification of

a "high voltage" are the possibility of causing

a spark in air, and the danger of electric shock

by contact or proximity.

In electric power transmission engineering,

high voltage is usually considered any

voltage over approximately 35,000 volts.

In electric power transmission engineering

this refers to equipment designed for more than

345,000 volts between conductors. In

electronics systems, a power supply that

provides greater than 275,000 volts is known

as an "EHV Power Supply". It is often used in

experiments in physics.

With the increase in transmission voltage, for same amount of

power to be transmitted current in the line decreases which reduces

I2R losses. This will lead to increase in transmission efficiency.

With decrease in transmission current, size of conductor required

reduces which decreases the volume of conductor.

The transmission capacity is proportional to square of operating

voltages. Thus the transmission capacity of line increases with

increase in voltage.

With increase in level of transmission voltage, the installation cost of

the transmission line per km decreases.

It is economical with EHV transmission to interconnect the power

systems on a large scale.

The no. of circuits and the land requirement for transmission

decreases with the use of higher transmission voltages.

The major advantages are:

Reduction in the current.

Reduction in the losses.

Reduction in volume of conductor material required.

Decrease in voltage drop & improvement of voltage regulation.

Increase in Transmission Efficiency.

Increased power handling capacity.

The no. of circuits & the land requirement reduces as transmission

voltage increases.

The total line cost per MW per km decreases considerably with the

increase in line voltage.

The major disadvantages are:

Corona loss & radio interference

Line supports

Erection difficulties

Insulation needs

The cost of transformers, switchgear equipments & protective

equipments increases with increase in transmission line voltage.

The EHV lines generates electrostatic effects which are harmful to

human beings & animals.

DISTRIBUTION LINE WITH NO GROUND WIRE

Dual 345 KV transmission lines

In addition to phase conductors, a transmission line usually includes one or two

steel wires called ground (shield) wires. These wires are electrically connected to

the tower and to the ground, and, therefore, are at ground potential.

In large transmission lines, these

wires are located above the

phase conductors, shielding them

from lightning.

A typical line route will involve the use of three main types of tower. They are as follows:

1) Suspension Tower

2) Deviation Tower

3) Terminal Tower

TYPES OF POLES

Type & Size of Conductors

An overhead transmission line usually consists of three conductors or

bundles of conductors containing the three phases of the power system.

The conductors are usually aluminum cable steel reinforced (ACSR),

which are steel core (for strength) and aluminum wires (having low

resistance) wrapped around the core.

Transmission lines are characterized by a series

resistance, inductance, and shunt capacitance

per unit length. These values determine the power-

carrying capacity of the transmission line and the

voltage drop across it at full load.

ERECTION OF HT LINE

Erection of HT line includes installation of poles/towers, stringing of conductors, Earthing of poles, fixing of anticlimbing device, etc.

Installation of poles/towers.

Stringing of conductors.

Earthing of poles.

Anticlimbing Device.

Danger Signboard.

Corona

Sag

Skin Effect

Ferranti Effect

SAG CALCULATION

Sag determines electrical clearances, right-of-way width(blowout),uplift (strain),thermal rating

Sag is a factor in electrical & magnetic fields, Aeolian vibration (h/w),ice galloping

Tension determines structure angle/dead end/broken wire loads

Tension limits determine conductor system safety factors, vibration & structure cost

Sag D

Span

Tension H

D (sag at belly)

Max tension

(s/2,d)end support

H=horizontal component of Tension(lb)T=Maximum tension(lb)x, y=Wire location in x y coordinates(0,0) is the lowest point(ft)D=Maximum sag(ft)L=Conductor length(ft)w=Conductor weight(lb/ft)S=Span length(ft)

SAFETY ASPECTS:

Clearance.

Earthwire.

Voltages of greater than 50 V applied across dry unbroken

human skin are capable of producing heart fibrillation if they

produce electric currents in body tissues which happen to pass

through the chest area.

The electrocution danger is mostly determined by the low

electrical conductivity of dry human skin.

(International safety symbol "Caution, risk of electric shock" (ISO 3864), colloquially

known as high voltage symbol)

Accidental contact with high voltage supplying sufficient energy will

usually result in severe injury or death.

low-energy exposure to high voltage may be harmless, such as the

spark produced in a dry climate when touching a doorknob after walking

across a carpeted floor.

1) Other factors (e.g. neighbourhood factors, square footage, size of lot, irrigation potential) are much more likely than overhead transmission lines to be major determinants of the sales price of property.

2) Effects are most likely to occur to property crossed by or immediately next to the line, but some impacts have been measured at longer distances.

3) Positive impacts may also occur, where the right-of-way is attractively landscaped or developed for recreational use.

4) Impacts may be greater for smaller properties than for larger properties.

REFERENCES

1) Project in Electrical, Electronics, Instrumentation and Computer Engineering by Dr. S.K.Bhattacharya & Dr.S.Chatterjee.

2) Principles of Power System by V.K.Mehta & Rohit Mehta

3) www.nationalgrid.com/uk/senseofplace

4) http://www.electrical4u.com/ferranti-effect-in-power-system/

5) http://www.electrical4u.com/skin-effect-in-transmission-lines/

6) Power System Engineering, Nagrath & Kothery, TMH.

7) Elements of power system analysis, C.L. Wodhwa, New Age International.

8) Electrical Power System, Ashfaq Hussain, CBS Publishers & Distributors.

9) A Text book on Power system Engineering, Soni, Gupta, Bhatnagar & Chakrabarti, Dhanpat Rai & Co.

10) http://www.google.com/

THANK YOU