UNIVERSITY OF NAIROBI -...

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UNIVERSITY OF NAIROBI

COLLEGE OF ARCHITECTURE AND ENGINEERING

DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING

PROJECT TITLE: UPRATING OF TRANSMISSION LINES-A CASE STUDY OF

132KV DANDORA – JUJA RD LINES I & II

PROJECT INDEX: 105

NAME: WANGARI KEITH MACHARIA

REG. NO.: F17/40182/2011

SUPERVISOR: DR. C. WEKESA

EXAMINER: PROF. M. MANG’OLI

Project report submitted in partial fulfillment of the requirement for the award of

Bachelor of Science Degree in Electrical and Electronic Engineering of the

University of Nairobi.

DATE OF SUBMISSION: 16TH MAY 2016

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DECLARATION OF ORIGINALITY

1) I understand what plagiarism is and I am aware of the university policy in this

regard.

2) I declare that this final year project report is my original work and has not been

submitted elsewhere for examination, award of a degree or publication. Where other

people’s work or my own work has been used, this has properly been acknowledged

and referenced in accordance with the University of Nairobi’s requirements.

3) I have not sought or used the services of any professional agencies to produce this

work

4) I have not allowed, and shall not allow anyone to copy my work with the intention

of passing it off as his/her own work.

5) I understand that any false claim in respect of this work shall result in disciplinary

action, in accordance with University anti-plagiarism policy.

Signature:

……………………………………………………………………………………

Date:

……………………………………………………………………………………

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DEDICATION

I dedicate this to my family, friends and all those who helped me through. Thank you for

your unwavering love and support.

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ACKNOWLEDGEMENT.

I would like to acknowledge the department of Electrical and Information Engineering

for entrusting me with this project. I thank my supervisor, DR. C. Wekesa for guiding

me throughout this endeavour. His insightful guidance cannot go unmentioned.

I would also like to thank my family for their hard work and dedication in ensuring

that I have the chance to pursue this degree.

I would also like to thank my friends and fellow classmates who believed in me and

encouraged me to always push on.

Last but not least, I would like to thank God for the gift of life, health and all the

blessings that have enabled me to come this far and to finish this project.

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TABLE OF CONTENTS

Contents UNIVERSITY OF NAIROBI ............................................................................................................. - 1 -

DECLARATION OF ORIGINALITY .......................................................................................................... - 2 -

DEDICATION ........................................................................................................................................ - 3 -

ACKNOWLEDGEMENT. ........................................................................................................................ - 4 -

TABLE OF CONTENTS ........................................................................................................................... - 5 -

ABSTRACT ............................................................................................................................................ - 7 -

1 CHAPTER 1................................................................................................................................... - 8 -

1.1 Introduction ........................................................................................................................ - 8 -

1.2 Main objective .................................................................................................................... - 9 -

1.3 Specific objective ................................................................................................................ - 9 -

1.4 Problem statement ........................................................................................................... - 10 -

2 CHAPTER 2: LITERATURE REVIEW. ............................................................................................ - 12 -

2.1 Growth in demand for power in the past present and the near future ........................... - 12 -

2.2 Right of way hinderances (ROW) ...................................................................................... - 12 -

2.3 Methods of increasing power flow through a transmission line. ..................................... - 13 -

2.3.1 Definition of uprating/upgrading. ............................................................................. - 13 -

2.3.2 Use of series capacitors and FACTS devices. ............................................................. - 14 -

2.3.3 Construction of high surge impedance line. ............................................................. - 16 -

2.3.4 Enhanced system and equipment monitoring .......................................................... - 17 -

2.3.5 Conversion of 3-phase systems to 6-phase systems. ............................................... - 17 -

2.4 Expanding Existing Transmission Capacity Technology .................................................... - 17 -

2.5 Fundamentals of Power Transfer Limits ........................................................................... - 18 -

2.5.1 Surge Impedance Loading ......................................................................................... - 18 -

2.5.2 Thermal Limits ........................................................................................................... - 19 -

2.5.3 System Limits ............................................................................................................ - 20 -

2.5.4 Increasing Thermal Limits ......................................................................................... - 20 -

2.5.5 Improved Transmission Structures ........................................................................... - 21 -

2.5.6 Uprating .................................................................................................................... - 21 -

2.6 Conductor hardware and accessories ............................................................................... - 47 -

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2.7 Conductor selection .......................................................................................................... - 47 -

3 CHAPTER 3.METHODOLOGY ..................................................................................................... - 50 -

3.1 Introduction ...................................................................................................................... - 50 -

3.2 Formulation ....................................................................................................................... - 50 -

3.2.1 Overhead line rating calculations ............................................................................. - 50 -

3.2.2 Sag-Tension calculations ........................................................................................... - 52 -

4 CHAPTER 4: RESULTS AND DISCUSSION .................................................................................... - 54 -

4.1 Results ............................................................................................................................... - 54 -

4.2 Discussion .......................................................................................................................... - 59 -

5 CHAPTER 5: CONCLUSION AND RECOMMENDATION ............................................................... - 61 -

5.1 Conclusion ......................................................................................................................... - 61 -

5.2 Recommendation .............................................................................................................. - 61 -

6 References ................................................................................................................................ - 62 -

7 Appendix ................................................................................................................................... - 63 -

8 Abbreviations ............................................................................................................................ - 66 -

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ABSTRACT

Due to the increase in demand for power, uprating of overhead transmission lines has

now become the most common way of solving this progressive increase in demand. It

is not always necessary to construct new transmission lines so that we can add the

transmission capacity of the existing transmission line .Uprating of overhead line by

increasing its current carrying capacity allows an increase in its power transfer

capability. This report examines the technical facts considered before the current

carrying capacity of a conductor can be increased, it also describes the methods of

uprating the transmission line and the factors to consider. The report also considers a

case of an existing two 132kv lines from Dandora to Juja road substations. The

transformer in the Dandora substation is rated 200MW but each line is currently

carrying 143 MW and can carry a maximum of 165Mw each when overloaded, thus

this report will also give a solution on how to maximize power from the transformers

in the substation to the other substation or to the load Centre .The two parallel lines

are always operated at or should carry 80% of the line rating for reliability and

contingency too. In our case the lines are operating normally at 71.5% the rated power

and when the power is increased to 80% the lines are overloaded which shouldn’t be

the case. The two lines on study are part of the many lines under the utilities company

The Kenya Power and Lighting Company Ltd (KPLC) .KPLC is a key player in the

electricity sector with the mandate to purchase bulk power from Kenya generating

company (kengen), Independent power producers (IPP) and transmits it to its load

centers via the transmission lines, distributes and retails the electricity to customers

throughout Kenya. The source of generation are hydro-electric, Geothermal, Thermal,

wind and Biomass.

The Kenya power transmission system is an interconnection of high voltage

transmission lines. This interconnection is known as the Transmission network or the

Grid. The Kenyan grid currently consists of 132KV and 220KV lines and

substations.400KV lines are currently under constructions and will connected to the

system in the future.

The total length in kilometers of the 220kv is 1,331KM while the total length in

kilometers of 132KV lines is 2,211KM. The two 132kv lines under study which runs

from Dandora to Juja road substations measures 2KM each.

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1 CHAPTER 1

1.1 Introduction

The increase in power demand has caused flow of power to increase in the existing

electrical transmission lines too.

There are several factors which have caused this increase:

Firstly, the technological growth has greatly led to the increase in demand for

electrical power. Most of the industrial machines, houses, household appliances,

electronic gadgets etc. uses power. The affordability and availability of the appliances

and gadgets have caused a significant demand for power nowadays as compared to

some years ago, and the growth is expected to go on as time goes by. Also increase in

population and the government subsidising the power connection fee has also led to

many homes being connected the national grid.

Secondly, the removal of state restrictions and regulation in regards to achieving

vision 2030 has led to increase in demand. I.e. nowadays the connection fee can be

paid in instalments over years through the monthly power bills and this gives each

homestead in the country a chance to be connected to the grid. Also the consequent

changes on generation points connected to the transmission system has caused major

changes in the power flows across transmission lines.ie when the demand gets high

during peak hours the generation points increase the power generated to meet the load

demand and this in turn affects the conductor design properties. The losses in the lines

also causes injection of extra power in the transmission system to cater for the losses

and meet the demand and this too results in overloading the conductor.

As a result of the increased power demand, some lines are operated near their

ampacity limit. Ampacity or thermal rating is the maximum current a conductor can

carry to meet it design features to avoid its destruction and to meet its safety

standards.

An excess conductor temperature may result in exceeding the required conductor sag

with consequent dangerous reduction in the clearances to the ground .All these effects

caused by an excessive current could put public safety at risk. In order to solve these

problems new lines could be constructed. However, the high population growth which

has led to high population density has resulted to the high intensive use of land. This

has caused only a small piece of land put aside for electrical lines. As a consequence,

the legislation authorization and ruling on the right of way (ROW) for the

transmission lines, the public presentation of the project, the commissioning of the

project and the tendering process can take a lot of years while the demand still

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continues to increase therefore there is great pressure to increase the power flow in

existing right of ways using existing infrastructure as far as possible. Traditionally, the

upgrading of the line has been used in order to increase the line rating. The upgrading

involves increasing the line voltage or the number of conductors. The main problem of

these methods is the need to strengthen the towers. For this reason, methods without

the need to strengthen the towers that allow to increase line power flow securely and

safely, close to its ampacity limit, have been developed .One of the option is to

increase the ampacity of the line by conductor replacement. The new conductor needs

to have better properties as compared to the previous one such as lower sag-

temperature relations. I.e. the conductors sag isn’t affected much by the line

temperature. Another solution is real time monitoring of the conductor where factors

such as weather conditions i.e. wind and ice loading conditions in areas which

experiences winter are considered, conductor temperature, sag and tension are also

considered.

1.2 Main objective

One of the major reasons for uprating an existing transmission line is to maximize

utilization of the existing corridor for transfer of power. In situations where

construction of new lines is obstructed by the presence of ecologically sensitive areas,

forests or urban habitations, uprating of the existing transmission line is one of the

most appropriate solutions to meet the power flow requirements. In this project the

main objective is to uprate the existing 132kv Dandora – Juja road lines I & II which

currently have 400mm² ACSR (Aluminium core steel reinforced) conductor and

replace it with similar or small size of conductor which has almost twice the current

capacity of ACSR. This will be a high temperature-low sag conductor (HTLS) or high

capacity conductor.

Below are examples of HTLS conductors:

1. Aluminium Conductor Composite Core (ACCC) conductor.

2. Aluminium conductor core reinforced (ACCR) conductor.

3. Aluminium conductor steel supported conductor (ACSS) conductor.

4. GAP(Aluminium-zirconium strands which are steel reinforced)

conductor

They all have better thermal characteristics as compared to ACSR conductor

1.3 Specific objective

In situations where demand for power is increasing or is expected to increase in the

near future, it is highly recommendable to increase the power flow capacity of the

existing transmission line in the corridor through uprating rather than to construct a

new line. This can enable achievement of the required power demand at a very less

cost and in a very short duration as compared to construction of new lines. In this case

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study the maximum power that each line should carry is 200 MW, currently the line

carries 143MW due to thermal constraints. Since the transformers at Dandora

substation are rated 200 MW each, there is no power increase planned in near future

hence the need to uprate the two lines to Juja Road substation.

1.4 Problem statement

Challenge caused by increase in demand for affordable electricity has caused many

system planners and transmission engineers to try hard to find economical ways to

reduce grid congestion and improve grid reliability. In many cases, grid congestion

costs the utilities and the customers they serve millions of shillings annually

.Restrictions on permitting new lines and advances in conductor and related

technologies have changed the options available to planners and engineers trying to

solve these problems until now. However, there have been limited design tools

available that can help to show the differences between multiple conductor solutions.

Power grid congestion is a situation where the existing transmission line or

distribution line is unable to accommodate the required load during high demand

periods. Grid congestion affects the reliability and also causes a decrease in efficiency

because line losses increases greatly under high load conditions. If the transmission

lines are operated near their thermal limits, there would be a substantial loss during

high load conditions. An example of this was in 2004 in the western US where

congested transmission lines in California were unable to carry low-cost hydroelectric

power from the northwest to the southwest.

In addition to grid congestion, which is typically a function of a transmission

conductor's propensity to sag as it heats up because of its electrical resistance and

thermal properties, congested transmission lines also impact grid reliability. Should an

adjacent line fail or be taken out of service, the lines that remain in service can quickly

become overloaded. This can lead to a cascading outage, as was observed in the

eastern US in 2003. Current North American Electric Reliability Corp. (NERC)

initiatives may be further tightening acceptable conductor sag limits as it has become

apparent, in many cases, that aged conductors and ever changing under-build may

compromise safe clearances.

One of the most economical ways of addressing congestion is the use of a high-

capacity or high-temperature conductor. A widely adopted high-capacity conductor,

Aluminum Conductor Composite Core (ACCC), uses a high-strength, light-weight

carbon and glass fiber core that have a low coefficient of thermal expansion, virtually

eliminating thermal sag. The core's decreased weight compared to a steel core also

allows the incorporation of some 28 percent more aluminum in any given conductor

size. The added aluminum content decreases conductor resistance, so even under

heavily loaded conditions line losses are minimized.

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An ACCC conductor can carry twice the current of a conventional aluminum

conductor steel reinforced (ACSR) conductor. While an aluminum conductor steel

supported (ACSS)-high temperature version of ACSR-conductor is also capable of

carrying twice the current of a conventional ACSR conductor, because of its electrical

resistance, it does so at much higher operating temperatures. In many cases the ACSS

conductor's thermal sag can prevent its higher capacity from being fully realized. In

either case, under any load condition, the ACCC conductor's added aluminum content

and decreased resistance reduces line losses by 30 to 40 percent or more.

The ACCC conductor's high strength, low coefficient of thermal sag, superior self-

damping and resistance to load fatigue, corrosion resistance and other attributes can

help improve project economics on new and reconductoring projects in any

environment. Using ACCC to increase the capacity of an existing line can reduce or

eliminate the need to reinforce existing structures, which can save millions of shillings

and permitting challenges. For new lines, using ACCC can allow greater spans

between fewer and shorter structures, saving time and money, along with the added

and long-term energy efficiency benefits.

While increased capacity and reduced thermal sag have obvious advantages as

reduced line losses also translate into large savings for the utility company, the

consumer and the environment. When projects are considered as a whole, the early

choices made by planners and engineers can reduce the number of new structures or

modifications to existing towers, resulting in project savings that often exceed the cost

of the conductor entirely.

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2 CHAPTER 2: LITERATURE REVIEW.

2.1 Growth in demand for power in the past present and the near future

The increase in population growth, improved standards of living and advanced

technology in the country has caused a great rise in demand for power in the recent

years. The demand is also anticipated to increase as shown in the graph below thus the

need to increase the installed capacity. To increase the installed capacity we would

require constructing new transmission lines and also using some methods of

increasing the power transfer capabilities.

Figure 1. Growth in demand for power in Kenya.

2.2 Right of way hinderances (ROW)

To add power transfer capacity construction of new transmission lines has been the

traditional method used. However the public opposition for the construction of new

lines is also increasing. This is due to allocation of land for other amenities like roads,

railway lines and other public facilities. The increase in population has also led to

increase in population density thus fewer paths for transmission line construction. The

clearances has also to be catered for to keep the public safe but the increase in

constructions especially in urban areas is also becoming a major obstacle for utilities

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companies. Environmental factors and acquiring legal rights for overhead

transmission lines have also become a challenge too.

2.3 Methods of increasing power flow through a transmission line.

The following are methods of increasing power flow through a transmission line:

1) Uprating of transmission lines.

2) Upgrading of transmission lines.

3) Use of series capacitors and FACTS (flexible alternating current transmission

systems) devices.

4) Construction of high surge impedance line such as expanded bundle, compact

lines.

5) Enhanced system and equipment monitoring.

6) Conversion of 3-phase systems to 6-phase systems.

2.3.1 Definition of uprating/upgrading.

Power flow in a 3-phase system is given by P=√3*V*I.

Where: V is the line voltage.

I is the line current.

Thus the power flow in a transmission line can either be increased by increasing the

line voltage V or the line current I.

The modification of line that results to a higher current carrying capacity is referred to

as thermal uprating and the modification of the line that allows the line to operate at a

higher voltage is referred to as voltage upgrading.

2.3.1.1 Reasons for uprating/upgrading.

The main reason for uprating/upgrading a transmission line is to fully utilize the

existing path for transfer of power. In circumstances where construction of new lines

is hindered by ROW issues, ecologically sensitive areas, forests and even urban areas,

uprating /upgrading the existing transmission line is the most economical method of

increasing the power transfer capability of the transmission line.

Also in areas where the power demand is expected to grow in the future, it is highly

advisable to increase the power flow of any existing transmission line through

uprating or upgrading rather than construction of a new line. This can help in

achieving the power demand cheaply and in less time.

2.3.1.2 Comparison between uprating and upgrading.

Uprating is the best solution for increasing the power carrying capacity of a

transmission line where power flow is limited by thermal limitations such as in short

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lines where power flow is as much as twice the Surge Impedance Loading (SIL). In

transmission lines where stability reasons is the main concern especially in the long

lines, the increase in the power carrying capacity of the line is solved through

upgrading .Increasing the line voltage also reduces the line per unit reactance.

Upgrading also leads to a reduction in the voltage drop along the line thus improves

the voltage control. Upgrading also leads to an increase in MVA rating of the

transmission line in relation to uprating. However upgrading requires more capital

investment, more power outage time for construction thus resulting in poor reliability

and also replacement of some substation equipment. This is because the electrical

clearance of the line will have to be increased to cater for the increased sag if the same

conductor is to be used. The existing structure will also need some modification to

cater for clearances between the conductors. Thus it is advisable to prioritize uprating

to upgrading if the reliability, time and cost factors are to be considered.

The substation is already rated at 132KV and there is no expected increase in the line

voltage thus this also positions uprating of the line as the best method to increase the

power transfer capability.

2.3.2 Use of series capacitors and FACTS devices.

2.3.2.1 Series capacitors.

The use of series capacitors for compensation part of the inductive reactance of long

transmission line will increase the transmission line capacity. It also increases the

transient stability margins, optimizes load sharing between parallel transmission lines

and reduces the overall system losses.

Transmission line compensation means modification in electric properties of the

transmission line to increase the power transfer capability.

In series compensation, the main objective is to reduce the transfer reactance of the

line at power frequency by means of series capacitors. This increases the system

stability which in turn increases the power transfer capability of the line.

Series capacitors can be connected at one or both ends of the line. The line ends are

the locations of the capacitors. Mid-point series compensation is more effective in the

case of very long transmission lines. Series capacitors located at the line ends create

more complex protection problems than those installed at the center of the line. The

power transfer along a transmission line is shown below:

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Figure 2. Transmission line without series compensation

The active power over the uncompensated transmission line is given by

P= (𝐸𝑆∗𝐸𝑅

𝑋𝑡)* sin ð

Where:

ES- sending end voltage

ER- receiving end voltage

Xt- transfer reactance of the transmission line

ð – Load angle.

Higher voltage gives higher power flow limit. Higher voltage for the same power

gives lesser current thus reducing I²R losses. Series compensation has been applied to

mostly long transmission lines and other locations where the transmission distances

are great and where large power transfers over this distances is required.

Modern high voltage and extra high voltage transmission lines are series compensated

to improve the power system performance, to enhance power transfer capacity, to

enhance power flow control and voltage control and to decrease the capital

investment.

Figure 3. Transmission line with series compensation.

The active power transferred by the compensated transmission line is given by:

P= (𝐸𝑆∗𝐸𝑅

𝑋𝑡−𝑋𝑐)* sin ð

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The effects of series compensation are:

The lower line impedance improves the system stability.

The lower line impedance improves the voltage regulation.

Adding the series capacitance provides a method of controlling the division of

load among several lines.

Increasing the loading capacity of a line improves the utilization of the

transmission system and therefore returns on the capital investment.

Increase in power capacity as compared to uncompensated line.

2.3.2.2 FACTS based devices

A flexible alternating current transmission system (FACTS) is a system composed of

static equipment used for the A.C transmission of electrical energy. It enhances

controllability and increases the power transfer capability of the network.

In series compensation, the facts based device is connected in series with the power

system. It works as a controllable voltage source. All transmission lines experiences

series inductance. When a large current flow this causes a large voltage drop and to

compensate this, series capacitors are connected to decrease the effect of inductance.

It also improves the power factor.

In shunt compensation the power system is connected in shunt with the FACTS. It

works as a controllable current source.

2.3.3 Construction of high surge impedance line.

The magnitude of power that a given transmission line can carry safely depends on

various factors. These factors can be categorized into thermal and surge impedance

loading limits. For long lines the capacity is limited by its SIL level. A decrease in line

inductance and surge impedance would in turn increase the surge impedance loading

(SIL) which would result in increase in power transfer capability.

The surge impedance which is also known as the characteristic impedance is given by

the equation below.

Zo= √𝐿

𝐶

Where: L is the per unit impedance.

C is the per unit capacitance.

The SIL is equation is shown below

SIL (MVA) = √𝑉𝐿𝐿2

𝑍ₒ

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VLL is the line-line voltage of the transmission line.

2.3.4 Enhanced system and equipment monitoring

Installation of tension and sag monitors can help in monitoring the transmission line.

On a cool windless day when the air temperature and wind speed is low, and there is

no sun, the MVA rating may be higher than that of a hot windy day. The line rating

will vary in such a way that is partly predictable or partly random. Also the load

variation monitoring can help in determining when the lines will carry their maximum

limits. I.e. During peak times the demand is high thus the lines can be put to their

maximum capacity while during off-peak times when the demand is low the lines can

be operated below their limits. Thus the power transfer capability is maximized only

when the demand is high.

2.3.5 Conversion of 3-phase systems to 6-phase systems.

Six phase system is one of the multiphase power systems. Due to harmonics effects

and some other reasons six phase systems and six phase machines are not common but

six phase transmission lines are popular due to the following reasons:

1. Increased power transfer capability.

2. Better voltage regulation.

3. Better efficiency.

4. Greater stability and reliability.

2.4 Expanding Existing Transmission Capacity Technology

Complex technology is necessary to increase the power flow capacity on existing

power equipment (overhead lines and power transformers), power circuits (multiple

power equipment elements in series), and power system interfaces (multiple parallel

power circuits connecting power system regions). The following three issues are basic

to all approaches:

1. For overhead lines, increase in power flow capacity is dependent on line length,

original design, environmental regulations, the condition of structures and the type of

conductors used. Increase in a line’s thermal rating could range from between 5% to

100%.

2. Overhead lines are only part of the transmission line path (circuit). The lines are

terminated at substations by air disconnects, circuit breakers, and line traps. The

power flow through all of the circuit elements must be limited to avoid damaging the

line or the terminating equipment. The maximum allowable power flow over this

circuit may be limited by any one of the circuit elements. According to the currently

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used rating method, a facility rating must be the minimum of all ratings between

substations.

3. Increase in maximum allowable power flow through a component circuit or circuit

element does not necessarily yield a higher rating. This is because increased power

flow on an improved element may interfere with another element’s limits.

Transmission circuit ratings are often developed on a system basis, rather than on an

individual line basis. This is because the maximum power flow on the transmission

system is a function of the overall system topology (transmission lines, transformers,

generation, series and shunt compensation, and load). Many non-thermal system

considerations (such as sag, tension and voltage) can also limit the maximum power

flow on a specific transmission circuit. The overall limit may be set between operating

areas, irrespective of ownership or individual lines, and may change during a day

based on system conditions. Increasing the capacity on a single line by 100% would

not necessarily increase the system capacity by this amount. A separate parallel

facility may have a constraint after the flow increases by only 25%.

2.5 Fundamentals of Power Transfer Limits

The following describe technical aspects of electric power transfer that will help those

evaluating alternative strategies for increasing the transfer capability of the grid.

2.5.1 Surge Impedance Loading

The surge impedance loading (SIL) of a power transmission line is the nominal power

flow capacity based on the design characteristics for the line and its operating voltage.

SIL is governed more by the overall geometry of the line and its operating voltage and

less by the conductor size. SIL is independent of the line length. SIL is not the

maximum that a particular line can carry, but rather a benchmark that can be used to

compare lines of different designs and voltage rating. SIL is a useful concept to

compare different transmission lines.

SIL (MVA) = √𝑉𝑙𝑙2

𝑍ₒ

VLL is the line-line voltage of the transmission line.

Zₒ is the lines characteristic impedance which is a function of the line’s inductance

and capacitance.

For an overhead transmission line, typical surge impedance is around 300 ohms,

compared to a cable, which may be 50 ohms or less. At 345 kV, the SIL of an

overhead line is on the order of 400 MW. Short lines may be able to carry 800 MW or

more. Long lines of the same construction may be limited to less than 400 MW by

system considerations. Underground transmission cables always operate very far

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below SIL because of limitations on heat dissipation. As a result, underground

transmission cables are a net source of reactive power (vars) to the system.

Reactive loading and losses can become a limiting problem if a significant number of

the lines are loaded above their SIL. As loading increases appreciably above SIL for

many lines in the system, the reactive losses will increase in relation to the square of

the current and the line reactance. Adding high-capacity lines instead of improving the

power transfer capability of the system could further increase the reactive losses and

consequently further hinder power transfers.

2.5.2 Thermal Limits

Thermal limits are the maximum flows that can be permitted through a transmission

circuit, either on a continuous basis or for a short duration, based on the circuit design.

The design parameters include the conductor type, conductor bundles, ambient

temperature, wind speed, ice loading, and span length. The thermal limitation is

critical in cases of lower voltage lines of 80 km or less.

At extra-high voltage (345 kV and above), environmental considerations, such as

corona discharge and field effects, dictate line designs and usually result in high

thermal capabilities, which can exceed the realistic power transfer. For extra-high

voltage transmission, line terminating equipment, such as wave traps and substations,

impose a thermal limit rather than the line itself. Consequently, thermal limits are

significant only for short lines at 138 kV and below.

The process of selecting a thermal rating for an overhead line can be fairly complex or

simple. Ratings are published by conductor manufacturers for a range of conservative

weather assumptions and conductor temperature limits. Ratings can also be

determined from field measurements of sag, wind direction and strength, solar

insolation, and other variables.

As power flow increases in a bare overhead power line, the conductors, connectors,

and associated hardware are heated because of the ohmic losses. Typically, lines that

are thermally limited are the shorter lines in the system and the economic cost of

electrical losses may be tolerable. However, potential damage to conductor systems or

safety concerns occasioned by violation of minimum clearances remains a concern

and must be catered for.

Thermal ratings for overhead lines are defined in amperes or megavolt amperes

(MVA) with an associated duration and, possibly, by frequency of occurrence.

Consequently, one line may have a continuous thermal rating of 100 MVA; a 4-hour,

long-time emergency rating of 115 MVA; and a 15-minute, short-time emergency

rating of 130 MVA. The system operator would understand these ratings to mean that

the power flow on this line could reach but not exceed 100 MVA indefinitely. Also, if

the flow exceeds 100 MVA, but is less than 115 MVA, the operator must reduce the

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flow to below 100 MVA within the next 4 hours. If the flow exceeds 115 MVA, the

operator must reduce it to below 100 MVA within 15 minutes. The temperature limits

on these lines typically serve to limit the loss of conductor tensile strength to less than

10% over the life of the line. It may be possible to exceed the thermal limits of lines

and accept some loss of life provided safe clearances are maintained especially for

lines that are scheduled for replacement or upgrade in the near future.

2.5.3 System Limits

System limits are functions of transmission line reactance in relation to the overall

power system. Series reactance, shunt admittance, and their combination can alter

system transfer limits. System planners have long recognized this relationship,

particularly where there are prospects of changing the line surge impedance, either by

adding equipment (e.g., series capacitors) or by modifying the line itself (e.g.,

reconductoring, voltage upgrading). Transmission line series inductive reactance is

determined by conductor size, phase spacing, number of conductors, relative phasing

(double-circuit lines), and line configuration. In long high-voltage overhead

transmission lines, the series reactance is larger than the series resistance and is

dominant. For this reason, simple reconductoring of many long transmission lines,

with no change to structure geometry, results in only minor changes in system power

flows.

2.5.4 Increasing Thermal Limits

The thermal limits of the conductor are the limiting factor in the capabilities of

transmission lines. As electricity flows through a transmission line, heat is produced

due to the flow of current through the resistance of the conductor. As the current

flowing through the conductor increases, additional heat is produced, which causes the

conductors temperature to increase. The temperature is a function of the electrical

current and the environmental conditions (temperature, humidity, and wind speed). If

the conductor becomes too hot, one of two problems may result.

1. Excessive heat may permanently damage the conductor. Each transmission line

has a maximum amount of power that can flow over it without damage.

2. Increasing temperature may cause the line to physically sag below design levels,

resulting in increased risk of injury to the public and conductor damage as well as

line outages. The line must not touch anything including the ground. Physical sag of

the line can be reduced by using certain types of conductors.

Other important constraints are the level of electric and magnetic fields produced

(e.g., electric fields increase as the conductor gets closer to the ground), the maximum

structure loads during occasional high wind and ice loads, and the maximum

temperature at which the energized conductors are allowed to operate. Given standard

- 21 -

worst-case weather conditions, the thermal rating of an existing line is determined by

the maximum allowable conductor temperature. Thus, uprating (adding more current

to increase power transfer capability) such lines without reconductoring normally

requires getting ways to maintain electrical clearances above the ground when

operating at a higher conductor temperature. To protect against problems resulting

from thermal overloads on transmission lines utilities companies install relays. A relay

senses the amount of power flowing through a transmission line and operates a circuit

breaker to interrupt the power flow on the line. If it exceeds the thermal limit of the

line then the power will then flow through parallel paths. The increased loading along

the parallel paths creates the potential for an overload condition on other transmission

lines. If the system is not properly designed, operated, and maintained, thermal

overloads can lead to cascading outages of transmission lines and system breakup.

Transmission line capacity can be increased through improvements in transmission

tower design (to compensate for physical sag) and increases in conductor current

capabilities (to withstand more heat). The ability to accurately determine the

conductor thermal condition at any point in time (monitoring) is also helpful in

maintaining the line.

2.5.5 Improved Transmission Structures

Adaptations can be made to accommodate physical sag resulting from increased

transmission capacity on existing lines. Ground clearance on specific spans can be

increased by installing additional structures mid-span, if the ground contours and

permitting restrictions allow. Clearance can also be increased by modifying the

existing structures to raise the conductor attachment points. Digging the ground in

between the support structures can also be used as a method of increasing the

clearance. Alternatively existing structures can be replaced with taller structures.

These methods do not increase conductor tension, minimizing the need to replace

angle and dead-end structures. Increasing ground clearance typically results in only

modest increases in allowable ampacity (electricity through the line) before cost

becomes high.

2.5.6 Uprating

2.5.6.1 Basics of uprating

Thermal uprating is based on the fact that the tower structure / geometry, air gap

clearances and conductor bundle configuration are generally limited by the voltage of

the transmission line. If we keep the line voltage constant and we vary the line current

to a greater value we may be able to increase the power transfer capability of the

transmission line without possible need of changing the tower structure/ geometry.

Thermal uprating methods are cheapest and less time consuming as compared to other

methods.

- 22 -

2.5.6.2 Methods of uprating.

Increase in ampacity of a transmission line may be achieved through the following

methods.

2.5.6.2.1 Increase conductor rating by changing the thermal rating criteria

The maximum operating temperature of an ACSR conductor can be reached

without getting to the annealing point of the aluminium strands. This results to

an increase in the MVA of the line.

The ACSR conductor experiences a loss in its composite strength if operated

above 95 ͦ C for an extended period of time. The strength of the steel core is not

affected for temperatures below 300 ͦ C. The increase in maximum sag of the

conductor due to an increase in the maximum operating temperature of around

5-10 ͦ C is only marginal. I.e. the approximate increase in sag is 0.2 m for 5 ͦ C

increase and 0.4 m for 10 ͦ C increase while the approximate increase in MVA

for a 400KV DC line is 150MVA and 300MVA respectively.

If the increase in sag of the transmission line lies within the safety margin,

there is no need for construction of a new tower structure or refurbishment of

the existing tower. The above method has an advantage which is:

There will be no purchase of any new conductor.

No line outages.

Thus it is therefore the most cost effective and effortless method of increasing the

MVA rating of a transmission line. If the electrical clearance corresponding to the new

higher current carrying conductor is not enough then the following should be done:

i. The supports structure must be raised.

ii. The conductor tension should be increased.

iii. The suspension clamp positions should be changed.

This method may not be economical since it results to a small increase in the MVA

rating of the transmission line. It is the best solution where only a marginal increase in

power flow capacity of the transmission line is required. It also helps in getting rid of

cost and time of a new transmission line construction.

Conductor

temperature

(°C)

MVA rating Maximum sag

(m)

Span (m) Tension (N)

40 16 0.415 100 8568.22

65 55.9 0.571 100 5622.24

- 23 -

75 64.6 0.663 100 4659.04

Table 1. An indication in the variation in sag and MVA rating as a function of

conductor temperature.

The calculations were done considering an ambient temperature of 30 °C.

The conductor parameters were:

Stranding (No/diameter. mm) – 6/4.1 mm

Break load (N) -27200

Cross-sectional (area sq.mm) - 75

Modulus of elasticity (N/mm²) -79000

Coefficient of expansion- (I °C) – 1.91 * 10^-5

Weight (Kg/Km) – 320

Conductor diameter (mm) – 12.3

Calculating conditions:

Safety factor – 2

Radial ice thickness (mm) -0

Wind pressure (N/mm²) – 400

Initial conductor temperature (ͦ C) - 40

- 24 -

Figure 4. A graph showing how an increase in temperature results to an increase in

MVA rating.

2.5.6.2.2 Dynamic environment rating.

Installation of tension and sag monitors can help in dynamic line rating. On a

cool windless day when the air temperature and wind speed is low, and there is

no sun, the MVA rating may be higher than that of a hot windy day. The line

rating will vary in such a way that is partly predictable or partly random.

The cost of monitoring the system may be a small percentage as compared to

the construction of a new line. It also has the advantage of no service outage.

This method does not change the maximum capacity of the existing conductor

but it allows the maximum utilization of the conductor.

- 25 -

2.5.6.2.3 Increasing the conductor area

The increase in the aluminium or aluminium content of the existing conductor

results to a decrease in the conductor resistance.it is shown by the formula

below.

R= 𝜌𝐿

𝐴

Where: R is the resistance.

ρ is the conductor resistivity.

L is the conductor length.

A is the conductor area.

This result to an increase in ampacity of the conductor. It can be achieved by

the following two methods:

i. Adding new conductors to the existing conductor.

ii. Replacing the existing conductor with new conductor of different size

and shape.

ACSR Dog 100 sq.mm ACSR Zebra 400 sq.mm ACSR curlew 600 sq.mm

Temperature(°C) Current

(A)


(A)


(A)

50 194 50 395 50 432

75 335 75 774 75 869

100 421 100 998 100 1126

125 487 125 1167 125 1319

150 539 150 1304 150 1477

175 584 175 1423 175 1614

200 624 200 1529 200 1736

Table 2. How the increase in conductor size affects the current

carrying capability of a conductor at different working temperatures.

- 26 -

Figure 5. A graph showing how conductor cross-sectional area affects its

current carrying capability.

2.5.6.2.3.1 There are certain factors to consider before increasing the conductor

area

a) The higher the conductor area the greater the weight. An increase in

conductor weight results to an increase in vertical load and an increase

in tension too if the conductors sag is to be limited. The increase in

tension will lead to tower reinforcement. The increased area may also

increase the wind loading on the conductor thus increasing the vertical

and transverse load on the tower structure. To get rid of increased outer

conductor’s diameter, conductor with trapezoidal strands can be used

instead of circular strands. In this conductor the aluminium area of the

conductor is increased without overall increase in diameter. This helps

in increasing the ampacity with less effect on mechanical loading of the

transmission line rather than using the latter.

- 27 -

b) The increase in weight leads to an increase in the conductors sag. If the

conductor tension values are limited to those of the existing conductor,

the following can be done to cater for the increased sag:

Modifying the towers to increase clearance.

Installation of new towers in areas with critical spans.

Installation of negative sag devices along the conductor. The

device is altered by the changes in temperature. When there is an

increase in temperature, the conductor expands and there is an

increase in its length. The device changes geometrically to cater

for the increase in sag. As the conductor temperature decreases

the sag decrease too and the device retains its normal shape.

Excavation of key areas to increase ground clearance.

2.5.6.2.4 Reconductoring using a conductor of higher ampacity.

Reconductoring is the process of replacing the existing conductor with a higher

ampacity one so that the thermal rating of the existing transmission line can be

increased. Reconductoring using a conductor of larger diameter than the current one

can lead to an increase in wind loading. Increase in wind loading will require

improvement of the existing structure to cater for the excess weight. Reconductoring

using conductor with the same diameter as original conductor but with higher thermal

rating can lead to higher ampacity with no need to reinforce the existing tower and

structures.

Therefore the line rating is limited by the following factors:

• The properties of the conductor material

• The environmental conditions surrounding the conductor.

• The ground clearance of the line.

Today, most overhead transmission lines are aluminum conductor steel reinforced

(ACSR) conductors. Steel can withstand temperatures up to 300°C with no changes in

its properties. Aluminum, however, experiences deterioration in mechanical properties

(annealing) when the temperature is higher than 90°C. The temperature is a function

of the electrical current and the environmental conditions.

The replacement conductors can be classified into two categories:

1. Conductors to be operated at temperatures at moderated temperatures

(Temperatures < 100° C.)

2. Conductors to be operated at high temperatures (Temperatures >100° C.)

- 28 -

2.5.6.2.4.1 Conductors for operation at moderate temperatures.

There are three types of conductors that operate at moderate temperatures:

a) AAAC (All aluminium alloy conductors).

b) Aluminium conductor aluminium alloy reinforced. (ACAR).

c) High conductivity AAAC.

The AAAC conductors have a higher strength to weight ratio as compared to

ACSR. If they are operated at the same percentage of the rated breaking strength

with ACSR, they can operate at a higher temperature than ACSR with the

maximum sag for the design catered for. Operating at the same percentage of rated

breaking strength however leads to much higher ratio of horizontal tension to the

conductor unit weight and this can cause problems to lines sensitive to vibration.

ACAR combines strands made from aluminium alloy and EC grade aluminium.

The use of EC grade aluminium increases the conductivity of the conductor. If the

number of the alloy strands is also increased, the mechanical strength of the

conductor is also increased. The use of ACAR to substitute ACSR depends mainly

on the allowable operating tension.

2.5.6.2.4.2 Conductors for operation at higher temperatures

By use of AAAC and ACAR conductors to replace ACSR conductor may not be

an economical solution since there is no much increase in current carrying capacity

of the transmission line as compared to the cost of replacing the line. Use of higher

operating temperatures conductors can be a better solution and can result in a

significant increase in thermal rating of the existing conductor; it is even twice in

some situations.

The conductors can be classified into two categories:

1. High temperature conductors

2. High temperature low-sag conductors

2.5.6.2.4.2.1 High temperature conductors

This type of conductors has the ability to operate at temperatures of at least 150°C.

Their sag increases linearly with increase in temperature. Among the most commonly

used high temperature conductors are:

2.5.6.2.4.2.1.1 TACSR (thermal resistant aluminium conductor steel

reinforced)

This conductor is made up of an inner steel core consisting of galvanized steel

wires and outer aluminium layers composed of aluminium-zirconium alloy

strands.

- 29 -

Figure 6. A figure showing the cross sectional area of a TACSR conductor.

The aluminium alloy has a higher resistivity when compared to hard drawn aluminium

but it can be operated to temperatures of up to 210°C thus increasing the power

carrying capacity.

There are different types of aluminium alloy conductors used in the formation of this

conductor. The alloys have the following properties:

Aluminium

alloy.

Conductivity

(%)

Tensile

strength (MPa)

Continuous

operating

temperature

(°C)

Current

carrying

capacity (%)

EC 1350 61 160 85 100

TAL 60 160 150 160

This type of conductor finds applications in the following areas:

In transmission lines where the current levels have to be 1.5 to 1.6 times higher

than the capacity of a normal ACSR.

In overhead lines in areas where corrosion caused by contact of two different

metals may occur.

In overhead transmission lines where low sag is not a limiting factor.

In transmission lines which can be operated safely at a continuous temperature

of 150°C.

In reconductoring without necessarily modifying the tower.

- 30 -

Table 3.The table below shows the technical comparison of ACSR panther

and TACSR conductor.

properties ACSR panther TACSR panther

Cross- sectional area (mm²) 262 262

Conductor Diameter (mm) 21 21

Weight (kg/km) 974 916

DC Resistance at 20°C temperature

(ohms/km)

0.139 0.12882

Maximum Operating Temperature

(°C)

75 150

Voltage Level (kV) 132 132

Line length (km) 1 1

Span (m) 325 325

Maintaining same ampacity in TACSR conductor

Calculation temperatures (°C) 75 73.43

Current to be maintained (A) 420 420

AC resistance (ohms/km) 0.1701 0.15658

Line losses (kw/circuit) 90 82.9

Power transferred (MW/circuit) 83.8 83.8

Ampacity at maximum operating temperature in TACSR conductor.

Calculation temperatures (°C) 75 150

Current (A) 420 893


Line losses (kw/circuit) 90 469

Power factor 0.9 0.9

Power transferred (MW/circuit) 83.8 178

Sag at the mentioned temperature

above and 0% wind (m)

7.244 9.81

Tension to be maintained at 32°c

and 100% wind.

4255 4253

The assumptions made:

Coefficient of emissivity= 0.6

Wind velocity = 0.6 m/s.

Solar absorption coefficient = 0.5

Average ambient temperature = 48°C.

Constant of mass temperature coefficient of

resistance of conductor per °C =0.004 for both

conductors.

Wind pressure = 117.96 kg/m².

- 31 -

Solar radiation = 1200 W/m².

From the above table the following remarks can be made:

1) TACSR can operate at a maximum temperature of 150°C while ACSR

operates at 85°C thus this boosts the current carrying capacity by 112%.

The ACSR carries 420 Amps by while TACSR carries 893 Amps at

their maximum operating temperatures.

The difference in currents: 893-420=473A

(473

420) ∗ 100 = 112.6%

2) The power transferred in MW by TACSR conductor at its maximum

operating temperature is 112% higher than that of ACSR.

Maximum ACSR panther power at its maximum operating temperature

– 83.8 MW.

Maximum ACSR panther power at its maximum operating temperature

– 178 MW.

Difference 178-83.8=94.2 MW

(94.2

83.8) ∗ 100=112.4%

2.5.6.2.4.2.1.2 High conductivity AAAC conductor (Al59)

The high conductivity all aluminium alloy conductor made of aluminium –

magnesium-silicon alloy strands has been widely used by utilities companies in

the world.

This conductor can carry 25-30% more current as compared to ACSR conductor

of the same size while the sag remains the same and the working tension is lesser

than that of ACSR.it also has lower resistance than ACSR thus the losses are

reduced. It also has a higher corrosion resistance as compared to alloy series of

AAAC conductors.

When comparing AL59 conductor with conventional AAAC and ACSR

conductors, the following points can be made:

Its ultimate tensile strength is lesser when compared to the above

conductors but it can be strung in the same tension.

If the span and working tension is maintained as the same, it will have

lower sag as compared to the above conductors. Thus this conductor can

be used in uprating the existing lines or in construction of new lines.

The table below shows options for reconductoring existing ACSR with AL59

conductor.

- 32 -

Table 4. The table below shows technical comparison of ACSR Dog and AL59

(19/2.84)

properties ACSR Dog AL59 (19/2.84)

Conductor Diameter (mm) 14.15 14.2



(ohms/km)

0.2792 0.2457



Span (m) 250 250

Maintaining same ampacity in AL59 conductor




Line losses (kw/circuit) 84.77 73.51

Ampacity at maximum operating temperature in both conductors.


Current (A) 288 409







5.255 5.84


and 100% wind.

2008 2008







resistance of conductor per °C =0.004 for ACSR

and 0.0039 for AL59.




- 33 -

1. The weight of AL59 conductor in kg/km is 16.24% less as compared

to the ACSR conductor.

Al 59 weight per km – 330

ACSR dog weight per km- 394

Difference: 394-330=64 64

394*100=16.24%

The decrease in weight shows that there is no need for structure

modification when reconductoring.

2. The DC resistance at temperature of 20°C of AL59 conductor is 12%

lesser as compared to that of ACSR thus increasing AL59’s ampacity

while reducing its line losses.

ACSR dog D.C resistance at 20°C – 0.2792

AL 59 D.C resistance at 20°C- 0.24750

Difference: 0.2792-0.24750=0.0317 0.0317

0.2792∗ 100=11.35%.

3. While maintaining the same ampacity, the line losses of AL59

conductor are 13.28% lesser when compared to that of ACSR.

ACSR dog line losses -84.77

AL 59 line losses -73.51

Difference: 84.77-73.51=11.26 kW. 11.26

84.77∗ 100=13.28%

4. When both conductors are operated at their maximum temperatures,

AL59 conductor carries 42% more current when compared to ACSR

conductor.

ACSR dog current- 288

AL 59 current -409

Difference: 409-288=121 121

288∗100= 42.01%.

5. The power transferred by the AL59 conductor is 42% more than that

of the ACSR conductor at their maximum operating temperature.

The power transfer at maximum operating currents.

ACSR dog-28.74 MW/cct

AL 59- 40.81

Difference: 40.81-28.74=12.07 MW/cct

12.07

28.74*100=41.99%

- 34 -

6. While maintaining the tension of ACSR at 32° and 100% wind, the

increase in sag is 0.585 for an increase in 121 amperes.

The difference in sag between ACSR dog and AL 59 at maximum

temperature and 0% wind.

Difference: 5.84-5.255=0.585

The difference in current at maximum operating temperature

409-288=121 A.

2.5.6.2.4.2.2 High temperature-low sag conductors

This type of conductors has the ability to operate continuously at temperatures of at

least 150°C. Their increase in sag is not linear at all temperatures due to knee-point

temperature. Knee-point temperature is the temperature which the core carries all the

tension in the conductor. The conductor experiences sag due to the expansion of the

steel core alone (The coefficient of linear expansion of steel conductor is lower than

the complete conductor). The higher the thermal expansion of the aluminium causes

all its stress to be carried by the steel core. Beyond the knee point temperature, the

new conductor coefficient will be the same as that of the core resulting in low sag

when operated at high temperatures.

Replacement of ACSR conductors in existing transmission line with such types of

conductors can therefore lead to an increase in the line carrying capacity without the

need for tower modification.

Commonly used HTLS conductors

2.5.6.2.4.2.2.1 INVAR

The INVAR conductor consists of a core of iron and nickel alloy which has a low

coefficient of thermal expansion. The outer layer of INVAR conductor is composed of

aluminium-zirconium alloy. This type of conductor can be operated at temperatures of

around 200°C at low sag.

This type of conductor has the following advantages:

Its current carrying capacity is 100% or more when compared to a conventional

ACSR conductor with the same diameter.

It has lower sag than ACSR conductor under same ampacity due to its INVAR

core.

Modification or reinforcement of the existing line is less or not required if the

INVAR conductor has the same diameter as the existing ACSR conductor to be

replaced.

- 35 -

Figure 7. A figure showing the cross-sectional area of a typical INVAR conductor.

The numerical data shows the option of using INVAR conductor for the

purpose of reconductoring in place of existing ACSR conductor.

Table 5. The table below shows the technical comparison of ACSR moose

and INVAR conductor.

properties ACSR moose INVAR




(ohms/km)

0.05595 0.0540


(°C)

75 210



Span (m) 400 400

Maintaining same ampacity in INVAR conductor





Power transferred (MW/circuit) 439 439

Ampacity at maximum operating temperature in INVAR conductor.


Current (A) 726 1957



- 36 -


Power transferred (MW/circuit) 439 1183.6



12.87 15.3


and 100% wind.

6603 6593








conductors.




1. Under the same diameter, the unit weight i.e. weight per km of

INVAR conductor is much less than that of ACSR conductor thus

when reconductoring there is no need for tower refurbishment or

modification.

INVAR weight/km-1950 kg

ACSR moose weight/km-2004 kg

Difference: 2004-1950=54 kg

2. The DC resistance at 20°C of INVAR conductor is 3.49% lesser

when compared to that of ACSR conductor thus increasing its

ampacity and reducing its line losses.

INVAR DC resistance at 20°C -0.0540

ACSR moose DC resistance at 20°C -0.05595

Difference: 0.05595-0.0540=0.00195

0.00195

0.05595*100=3.49%

3. INVAR conductor can operate at a maximum of 210°C while ACSR

conductor operates at maximum temperature of 75°C thus the

increase in its current carrying capacity is almost 170%.

At maximum operating temperature

ACSR current -726A

INVAR current – 1957A

Difference: 1957-726=1231A

1231

726*100=170%

- 37 -

4. The power transferred in MW by INVAR conductor at its maximum

operating temperature is 169.6% more as compared to that of ACSR

conductor.

Power at maximum operating temperature.

ACSR conductor- 439 MW/cct

INVAR conductor – 1183.6 MW/cct

Difference: 1183.6-439=744.6

744.6

439*100=169.6%

2.5.6.2.4.2.2.2 ACSS (Aluminium conductor steel supported)

The construction of this type of conductor is the same as that of ACSR except

that the aluminium strands are fully annealed. The annealed or 0-tempered

aluminium strands have a higher conductivity than hard drawn aluminium. The

hard drawn aluminium conductivity is 61.2% while that of annealed aluminium

is 63% as compared to copper which has 100% conductivity. The aluminium

strands don’t take any mechanical load thus can be operated at temperatures in

the order of 200°C without loss in their strength. When the complete conductor

is stressed, the aluminium elongates and transfers the entire load to the steel

core.

The conductor finds use in the following applications:

In areas where the current to be carried by a conductor is doubled under

the same tower loadings i.e. without the need to refurbish the tower.

ACSS with the same diameter as ACSR can be used to fulfill this

condition.

When the conductor is used in new lines, there can be reduction in cost

of the components i.e. the tower structures due to decreased sag in the

same amount of power transfer.

- 38 -

Figure 8. A figure showing the cross sectional area of a typical ACSS

conductor with trapezoidal aluminium strands.

The numerical data shows the option of using ACSS conductor for the purpose

of reconductoring in place of existing ACSR conductor.

Table 6. The table below shows the technical comparison of ACSR panther

and ACSS lark conductor.

Properties ACSR panther ACSS lark

Conductor Diameter (mm) 21 20.44



(ohms/km)

0.139 0.13535


(°C)

75 250



Span (m) 325 325

Maintaining same ampacity in ACSS conductor






Ampacity at maximum operating temperature in ACSS conductor.



- 39 -







7.244 10.56


and 100% wind.

4255 3653.5








conductors.




1. The DC resistance at 20°C of ACSS is 2.63% lesser than the ACSR

resistance thus the increase in ampacity.

DC resistance at 20°C

ACSR panther – 0.139

ACSS lark – 0.13535

Difference: 0.139-0.13535=0.00365

0.00365

0.139*100=2.63%

2. When operated at the same ampacity, the ACSS line loses are 2.89%

lesser than that of ACSR.

Under the same ampacity

ACSR panther line losses – 90MW/cct

ACSS lark line losses -87.4 MW/cct

Difference: 90-87.4=2.6

2.6

90*100=2.888%

3. The ACSS conductor can operate at a maximum temperature of

250°C while the ACSR operates at 75°C thus increasing its current

carrying capacity by 181%.


ACSR current -420A

ACSS current – 1180

- 40 -


760

420*100=180.95%

4. The power transferred at maximum conductor operating

temperatures in ACSS is 181% higher than ACSR.


ACSR power -83.8

ACSS power – 235.5

Difference: 235.5-83.8=151.7

151.7

83.8*100=181%

2.5.6.2.4.2.2.3 GAP conductor

This type of conductor involves a small gap maintained in between inner steel core

and outer aluminium-zirconium alloy layers. The steel core is the only one that is

tensioned and it carries the entire mechanical load. The increase in conductors sag

is determined by the coefficient of expansion of the steel core at all temperatures.

The core has low sag when operated at high temperatures in the order of 200°C.

Importance of these conductors

They have ultra-high strength steel core with temperature resistance of up to

250°C

The high temperature grease allows aluminium to move freely over the core

and protect the core from long term corrosion; the grease is resistant to

temperatures of up to 300°C.

The major drawback of these conductors is that the installation process is

complex.

This conductor does not need modification of existing tower structure if it were

to replace ACSR conductor of the same diameter.

- 41 -

Figure 9. A figure showing the cross sectional area of a typical GAP conductor.

The numerical data shows the option of using GAP conductor for the purpose


Table 7. The table below shows the technical comparison of ACSR zebra and

GAP conductor.

Properties ACSR zebra GAP



(ohms/km)

0.06868 0.0661


(°C)

75 210



Span (m) 350 350

Maintaining same ampacity in GAP conductor




Line losses (kw/circuit) 104.5 100


Ampacity at maximum operating temperature in GAP conductor.




- 42 -

Line losses (kw/circuit) 104.5 1010










conductors.




1. GAP conductor can operate at its maximum temperature of 210°C as

compared to that of ACSR at 75°C thus boosting up the current by

165% nearly 1.65 times.

At their maximum operating temperature.

ACSR zebra current – 641A

GAP current – 1696


1057

641*100=165%

2. The power transferred in MW of GAP conductor at its maximum

operating temperature is 165% higher as compared to that of ACSR.

At maximum operating temperature.

ACSR zebra power -213.2 MW/cct

GAP – 564.8 MW/cct

Difference: 564.8-213.2=351.6

351.6

213.2*100=165 %

2.5.6.2.4.2.2.4 ACCC (Aluminium conductor composite core)

This type of conductor consists of an outer core composed of o-tempered /annealed

aluminium trapezoidal strands and a carbon fibre composite inner core. The resistivity

of annealed aluminium is less than that of hard drawn aluminium or thermal resistant

aluminium alloys thus this leads to reduced line losses. The conductor can be operated

to temperatures of up to 180°C at lower sag. The carbon fibre core is 30% lighter thus

reduces its weight per unit length thus there is no need for structural modification if

the conductors diameter is the same as the one to be replaced.

- 43 -

The carbon fibre core also has a lower coefficient of thermal expansion thus the sag is

low at high operating temperatures hence increased current carrying capacity and no

need to increase the clearance.

Figure 10. A figure showing a typical cross- sectional area of an ACCC conductor.

The ACCC conductor has the following important features:

It has reduced thermal sag when compared to ACSR conductor.

It has reduced line losses when compared to ACSR conductor.

The annealed aluminium strands are in trapezoidal form and this result to an

additional aluminium content which improves the line conductivity while

reducing its losses.

It can reduce the cost of upgrading existing lines or in construction of new lines

due to its greater strength, reduced sag and its increased current carrying

capacity.

It does not corrode, rust or cause electrolysis with aluminium conductor or the

tower components thus it is suitable for polluted and zones near the ocean.

The conductor finds applications in the following areas:

1. Where reduction of line losses is required. Under equal loading

conditions they reduce the line losses by 30-40% compared to other

conductors of the same diameter and weight.

2. Ideal for reconductoring on existing line and upgradation of existing

line. They increase capacity by improving line clearance and reduce

strain on structure thus increasing their life.

The numerical data shows the option of using ACCC conductor for the purpose



and ACCC conductor.

Properties ACSR panther ACCC Casablanca

Conductor Diameter (mm) 21 20.5

Weight (kg/km) 974 834.4

- 44 -


(ohms/km)

0.139 0.1024


(°C)

75 180



Span (m) 325 325

Maintaining same ampacity in ACCC conductor






Ampacity at maximum operating temperature in ACCC conductor.









7.244 5.57


and 100% wind.

4255 3839.6








conductors.




1. The DC resistance at 20°C of ACCC conductor is 26.33% less than

ACSR thus increasing ampacity and reducing line losses.

The D.C resistance at 20°C

ACCC Casablanca – 0.1024

ACSR panther – 0.1390

- 45 -

Difference: 0.1390-0.1024=0.0366

0.0366

0.139*100=26.33

2. By maintaining same ampacity with ACSR conductor, the line losses of

ACCC conductor are 27.59 % lesser.

By maintaining the same ampacity

ACCC losses – 65.17 MW/cct

ACSR losses – 90 MW/cct

Difference: 90-65.17=24.83

24.83

90*100=27.59%

3. ACCC conductor maximum operating temperature is 175°C while

ACSR conductor operates at maximum temperature of 75°C. This

boosts its current carrying capacity by almost 166.43%.

At their maximum operating temperature.

ACCC current-1119A

ACSR current – 420A


699

420*100=166.43%

4. The power transfer in MW of ACCC conductor at its maximum

operating temperature is 166.45 % higher as compared to that of ACSR

conductor.

At their maximum operating temperature

ACCC power -223.3 MW/cct

ACSR power – 83.8 MW/cct

Difference: 223.3-83.8=139.5 139.5

83.8*100=166.45%

2.5.6.2.4.2.2.5 ACCR (Aluminium conductor composite reinforced)

This type of conductor consists of outer aluminium-zirconium alloy strands and an

inner composite core. The composite core consists of aluminium and aluminium oxide

matrix. The conductor can be operated continuously to temperatures of up to 200°C.

- 46 -

Figure 11. A figure showing the cross-sectional area of a typical ACCR conductor.


and ACCC conductor.

properties ACCR 336-T16 ACSR panther

Total diameter (mm) 21 21

Cross-sectional area

(mm²)

198 262


Resistance DC @ 20° C

(ohms/km)

0.1614 0.1390

Resistance AC @ 75° C

(ohms/km)

0.2779 0.1701

Voltage (Kv) 132 132

Current (A) 906 509

power (MVA) 207.2 116.3








conductors.



1. The weight per unit km of ACCR conductor is less by 64 kg when

compared to ACSR conductor thus there is no need for tower

reinforcement when reconductoring

ACCR weight per km-198

ACSR weight per km -262

- 47 -

Difference: 262-198=64 kg

2. At the same conductor cross sectional area , the ACCR current carrying

capability is 78% more than that of ACSR

ACCR current-906A

ACSR current- 509A

Difference: 906-509=397

397

509*100=77.99%

3. At the same conductor cross sectional area, the ACCR power carrying

capability is 78.16% more than that of ACSR.

ACCR power-207.2MW

ACSR power- 116.3 MW

Difference: 207.2-116.3=90.9

(90.9)/(116.3)*100= 78.16%

2.6 Conductor hardware and accessories

Uprating of the transmission line to higher current carrying capacity sometimes

involves replacement of associated hardware e.g. towers and conductor accessories

e.g. insulators etc. to cope with the increased current. The hardware is designed in

such a way that they have good heat dissipation characteristics due to the increase in

operating temperatures thus making the operation safe.

Magnetic heating of the clamp as a result of increased current passing through the

conductor also increases which results to an increase in magnetic losses. To solve this

problem ferrous clamp may be replaced with non-ferrous clamps to reduce the

magnetic losses.

Also due to the increase in conductor carrying capacity, the cross-arms distance might

also be increased to cater for insulation. The tower length might also be increased to

cater for clearances effect.

2.7 Conductor selection

Conductor selection can have a significant effect on both the short and long term

economic performance of transmission line projects. Since conductors are one of the

major cost components of a line design, selecting an appropriate conductor type and

size is essential for optimal operating efficiency. Due to this reason, a number of

systematic approaches for conductor selection have been developed.

The choice of appropriate conductor depends on:

- 48 -

Electrical load requirements.

The projections in load growth.

Support structure requirements.

Environmental considerations

Set regulations.

Cost of the project.

Some physical and economic factors that affect the choice of conductors are:

Increasing the conductor diameter results to increase in its weight, thus

the wind loading is increased on the support structures hence the need to

reinforce them.

Choosing a conductor with a higher resistance increases the power

losses along the line.

Thus the conductor selection should be based on the total system cost not the unit cost

of the conductor and the economic values it will offer as compared to other

conductors.

From the conductors discussed above, we see that they all have better characteristics

than ACSR conductor. For the purpose of reconductoring, we have to choose the

conductor with outstanding properties among them all.

Figure 12. A graph showing how the increase in temperature affects the cable sag

of different types of conductors.

- 49 -

Among all the conductors, the ACCC conductor has lowest sag with increase in

temperature thus this shows that there is no need for structure modification to increase

the clearance when reconductoring if the conductors of the same cross sectional area

are to be used.

Figure 13. A graph showing how increase in temperature affects the current

carrying capability of the different typesof conductors.

- 50 -

3 CHAPTER 3.METHODOLOGY

3.1 Introduction

This chapter gives the details on how reconductoring using a conductor of higher

ampacity as the best uprating method of an existing transmission line. The factors to

consider were the right of way hinderances, line losses, need for tower reinforcement

due to increase or decrease in the conductortension and weight, increase in power

transfer capability and ground clearance. The overall project economics was also a

determining factor.

3.2 Formulation

3.2.1 Overhead line rating calculations

Operating current I (A)= SQRT((convection loss-(solar absorption

coefficient*intensity of solar radiation*overall conductor diameter)+(PI*conductor

emissivity*stefans constant*overall conductor diameter)*((conductor temperature rise

above ambient+ambient temperature+273)^4 – (ambient temperature+273)^4)) /a.c

resistance at operating temperature and current)

A.C resistance at operating temperature and current Ra.c (ohms/cm)= direct current

resistance

Intensity of solar radiation Si (watts/cm²)=(intensity of solar radiation/10000)

Overall conductor diameter d(cm)=(diameter(mm)/10)

Convection loss Hc (watts/cm)= IF(wind velocity normal to conductor>= 20,

0.00138*(wind velocity equivalent*conductor diameter)^0.448 *conductor

temperature rise above ambient ,0.00128*(overall conductor diameter)^0.669

*(conductor temperature rise above ambient)^1.233

Conductor operating temperature (°C)=(conductor temperature rise above

ambient+ambient temperature)

Wind velocity equivalent Veq (cm/sec)=wind velocity normal to

conductor*(barometric pressure/760)*(293/(273+ambient temperature)

Barometric pressure b (mm Hg)=(10.33-(altitude above sea level/900)-

0.2357)*1000/13.6

Resistance at operating temperature Rt (Ω/cm)=resistance at 20°C*(1+temperature

coefficient of resistance*(conductor operating temperature-20))

Line rating S (MVA)=number of conductors in bundle*(√3*line voltage*operating

current)/1000000

- 51 -

Line losses = phase current² * phase resistance

Calculation constants:

Coefficient of emissivity =0.4

Wind velocity=0.6m/s

Solar absorption coefficient=0.6

Wind pressure=117.96 kg/m²

Solar radiation=1200W/m²

Radiative heat gain=15.096 W/m

Radiative heat loss=11.191 W/m

Convective heat loss=51.252 W/m

Joule heat gain=47.347 W/m

Stefans constant=5.67*10^-12 watts/cm²

Intensity of solar radiation=0.1 watts/cm²

Ambient temperature=35°C

Wind velocity normal to conductor=60 cm/sec

Frequency=50Hz

Temperature coefficient of resistance ρ (k^-1)=0.0036

- 52 -

3.2.2 Sag-Tension calculations

Figure 14. A figure showing the conductor sag at two different tower points.

A- Tower A.

B- Tower B.

Deflection is the same as the conductor sag

h- difference in height between tower A and B.

a- Distance from tower A to the conductors lowest point.

b- Distance from tower A to the conductors lowest point.

Ta- conductor tension at tower A.

Tb- conductor tension at tower B.

The ruling span formula is based on the fundamental assumption that the attachments

of the conductor to suspension structures between dead-end structures are flexible

enough to allow for longitudinal movement to equalize the tensions in adjacent spans

to the ruling span tension. If the temperature of a line segment with unequal spans is

raised uniformly, conductor in each span elongates in response to the temperature

change. This elongation increases the sag, thereby decreasing the tension. If the

suspension insulators remained stationary (without any rotation), there would be a

- 53 -

tension difference in adjacent spans of different lengths. However, the suspension

clamps displace longitudinally to provide force resolution at each suspension clamp.

For level spans, sag and slack in each suspension span at temperature T call be

calculated from the following parabolic equations.

Sag = Di, t = (w*Si²)/ (8*HR, t) = DR,t * (Si/SR)²

Slack = βi,t = Li,t-Si,t= (8* Di²,t)/(3*Si²) = (Si³*w²)/(24*H²R,t)

Rate of slack = βi,t / Si= (8*D²i,t)/(3*Si²) = (Si²*w²)/(24*H²R,t)

Ruling Span = SR = √ (S³1 + S³2 +. . .+S³n)/(S1 + S2 +. . .+Sn)

The rate of slack at temperature T can be calculated from the following equations:

(Rate of slack)i ,t =βi,t/Si=(Li,t – Si,t)/Si

Where Li,t = Li[1+α(T-Tₒ) +(HR,t-HR)/E*A]

Si,t =Si + (ᶑi - ᶑi-1),t

Substituting for Li,t and Si,t in the rate of slack equation:

Βi,t/Si=(Li*LR,t/(Si*LR)-1-(ᶑi - ᶑi-1),t/Si)

Finally the change in the rate of slack and span length due to a change in temperature

from Tₒ to T can be calculated from the equations below:

Change [βi,t/Si]Tₒ-T = change [βR,t/ SR] Tₒ-T - (ᶑi - ᶑi-1)/Si)

Where D-sag

S-span length

L-conductor length

Β-slack

Tₒ- conductor stringing tension

H- Horizontal conductor tension

w- Conductor unit weight

A- Conductor cross-sectional area

E- Conductor modulus of elasticity

α- Coefficient of thermal expansion

ᶑ - longitudinal horizontal movement of an infinitely flexible suspension clamp.

Subscripts

ₒ- at temperature Tₒ

t- at temperature T

R- Ruling span

- 54 -

4 CHAPTER 4: RESULTS AND DISCUSSION

4.1 Results As per the objective of the project, the current conductor ACSR canary 132 properties

were taken from KPLC and its properties compared with other conductors of almost

similar properties to see if reconductoring with a higher a capacity conductor would be

economical. All the calculations were done considering each conductor maximum

operating temperatures. The data was also used to come up with graphs.

Table 10. The table below shows different conductors properties at their maximum

working temperature.

Conductor

type

ACCR

Grosbea

k 636

ACCC

Amsterda

m 380

AAAC

Upas

BSEN5018

2

GAP

310

Goose

INVAR

(ZTACIR

)

ACSS

stilt

ACSR

Canary

132

Conductor

diameter(m

m)

25.5 23.55 24.71 22.6 20.04 20.31 26.12

Conductor

weight

(kg/km)

1079.5 1112.5 997.5 1227 761 1370 1721

D.C

resistance

@20°C

0.0828 0.0754 0.0917 0.0941 0.1580 0.0773 0.0763

4

Conductor

cross

sectional

area (mm²)

385 371.3 362.1 356.2 356 362.5 400

Maximum

operating

temperature

(°C)

200 180 95 200 200 200 75

Maximum

operating

current (A)

1342 1295 767 1217 908 1301 721

A.C

resistance at

75 °C

(Ω/km)

0.1371 0.1195 0.1172 0.1556 0.2607 0.1280 0.0923

Phase 1342.3 1295.4 766.9 1216.6 908.2 1300.9 721.3

- 55 -

current (A)

Line- line

voltage(KV)

132 132 132 132 132 132 132

A.C phase

resistance

(Ω)

0.1371 0.1195 0.1172 0.1556 0.2607 0.1280 0.0923

Power S

(MVA)

306.9 296.2 175.3 278.1 207.6 297.4 164.9

Line losses

I²R (KW)

247.023 200.528 68.929 230.30

6

215.032 216.62

0

48.021

Line losses

as a

percentage

of line

power (%)

0.0805 0.0677 0.0393 0.0828 0.1036 0.0728 0.0291

Figure 15. A graph showing the power vs. the cross sectional area relations of

different conductor types.

- 56 -

Figure 16. A graph showing the conductor current vs. the conductor weight per km

relations of different conductor types.

Conductor ACCR

Grosbe

ak 636

ACCC

Amsterd

am 380

AAAC

Upas

BSEN501

82

GAP

310

Goose

INVAR

(ZTACI

R)

ACSS

stilt

ACSR

Canary

132

Conductor

diameter

(mm)

25.5 23.55 24.71 22.6 20.04 20.31 26.12

Conductor

area (mm²)

385 383.7 362.1 356.2 356 362.5 400

Conductor

weight per km

1079.5 1112.5 997.5 1227 761 1370 1721

Safety factor 2 2 2 2 2 2 2

Modulus of

elasticity(N/m

m²)

57000 112300 57000 205900 139000 105000 79000

Tensile

strength (N)

113874 122600 106820 107500 89210 96740 82500

- 57 -

Stringing

tension (N)

53070.

40

60780.0

3

49753.92 48064.

07

36237.1

8

38496.

03

35194.

07

Ambient

temperature

(°C)

20-30 20-30 20-30 20-30 20-30 20-30 20-30

Operating

temperature

(°C)

200 180 95 200 200 200 75

Radial ice

thickness

(mm)

0 0 0 0 0 0 0

Wind pressure

(N/m²)

400 400 400 400 400 400 400

Table 11. A table of various characteristics of different conductors used for span

and stringing tension calculations.

Figure 17a. A table showing the results of span vs. sag characteristics of different

conductors from sag and tension calculator.

- 58 -

Figure 17b. A table showing the results of span vs. sag characteristics of different

conductors from sag and tension calculator.

Figure 18. A graph showing the span vs. sag characteristics of different types of

conductors

- 59 -

4.2 Discussion From the four uprating methods discussed earlier, that is:

i. Increasing the conductor rating by changing the thermal rating criteria.

ii. Dynamic environment rating.

iii. Increasing the conductor area.

iv. Reconductoring using conductor of higher ampacity.

We saw that the last option is the one that offers the best method of increasing

ampacity if the long term economic effects were to be put in place. The choice of

conductor selection when reconductoring is also another great factor since tower and

support structure strength has to be considered to ensure no other stress other than the

required is applied to the structure after reconductoring.

From the overhead transmission rating results, it is evident that all the conductors used

for comparison has lower weight per km value than the current ACSR canary

conductor thus this means that there will be no need for structure modification when

reconductoring. It’s caused by the lesser cross sectional area of the other conductors

due to different manufacturing method and the type of material used.

The conductors also have different maximum operating temperatures for ACCR,

GAP, INVAR and ACSS is 200°C while that of ACCC and ACSR is 180°C and 75°C

respectively. ACCR conductor has the highest current capacity at its maximum

operating temperature when compared to the other conductors, 1342 A. it is followed

closely by ACSS and ACCC conductors respectively. These conductors have lesser

diameter than the current ACSR canary conductor. Due to the increase in operating

temperature, when reconductoring using any of the listed conductors above, it would

be necessary to use conductor clamps with a higher heat resistance. The increase in

current leads to an increase in power transfer capability of the transmission line.

ACCR conductor has the highest power carrying capability when operated at its

maximum temperature according to our results, which is 306.9MVA. It is followed

closely by ACSS and ACCC conductor which stands at 297.4 MVA and 296.2 MVA.

ACSR conductor has the lowest power transfer capability among them all. The

conductor line losses also vary according to their carrying capacity and the line phase

resistance at their maximum operating temperatures. The line losses are given by I²R

where I is the current and R the resistance. We can see ACCR has the greatest line

losses but this is a small ratio of its power transfer capability when compared to other

conductors. ACSR has the least line losses but when compared to its power capability,

the ratio is greater than that of the other conductors.

From the power to cross-sectional area graph characteristics, we already saw that

increasing the conductor area is a method used to increase the power transfer

- 60 -

capability of a transmission line. However this statement doesn’t translate to the

results we got from the graph. This is because the ampacity of a transmission line

depends on many other factors apart from increasing the cross-sectional area. It’s

evident that ACSR conductor has the largest cross-sectional area among the

conductors while it has the least power transfer capability. The other conductors have

lesser surface area but more power carrying capability than the current ACSR canary

132. Reconductoring using the other conductors will be beneficial due to the increased

capacity with minimal or no tower modification. From the weight per km and

conductor carrying capacity graph, ACSR canary has the greatest weight per km and

carries the least current when compared to the other conductors. This factor is brought

about by ACSR maximum operating temperature. The reduced weight per km means

there will be no or minimal structure reinforcement or modification when

reconductoring thus the other conductors offer a greater advantage when compared to

ACSR. The decreased weight also means that there will be no extra pressure exerted

on the tower structure.

From the span versus sag characteristics graph, ACCC conductor has the lowest sag

with span increase. It is followed closely by AAAC and ACCR conductor

respectively. ACSR has greatest sag –span characteristics, 0.6m at a span of 100m

which was the basic span used for calculations.This leads to use of more materials in

the tower construction to cater for the sag and clearance. This offers another

advantage when reconductoring ACSR using the other conductors since they have

lower sag than the latter. This means there will be no need for structure modification

to cater for sag and clearance thus making it cheaper and faster to reconductor using

the HTLS conductors to increase the power transfer capability.

- 61 -

5 CHAPTER 5: CONCLUSION AND RECOMMENDATION

5.1 Conclusion The aim of the experiment was to study the methods of uprating a transmission line

and from the tabular and graphical results we can say that the objective was met. We

see that uprating the existing Dandora to Juja road lines I and II using a high

temperature-low sag conductor (HTLS) such as ACCR would not only increase the

power transfer capability of the lines but would also require less structural

modification. This would lead to great savings when compared to the construction of a

new line. The lesser line losses to power transfer ratio can be of great benefit to the

utility company. Reconductoring process won’t be affected by right of way

hinderances since the tower structure is already in its way. This makes the process not

only efficient method but also a faster way of increasing power transfer capability as

compared to new line construction.

5.2 Recommendation For many years in our country the utility companies has adopted the use of traditional

ACSR conductors, but the technological advancement has led to the introduction of

HTLS conductors. Adoption of this technology in the construction of new

transmission line or reconductoring the existing lines would lead to:

Improved power transfer capability.

Lesser line losses ratio compared to power transfer capability.

Low sag in the HTLS conductors’ causes reduction in tower construction

material since the conductor clearance won’t be a hindering factor.

The increased power carrying capability of HTLS conductor provides room for

future connection due to the rate of increase in population.

Replacement of the current ACSR conductor with ACCR since has the best power

transfer properties among all the other conductors and its sag-span characteristics

lie within the required range. This can lead to all the advantages stated above.

- 62 -

6 References

1) The approach to thermal uprating of Transmission line by. S.P.

Hoffmann, A.M. Clark.

2) Methods of increasing the rating of overhead lines by. I. Albizu, A. J.

Mazon, I. Zamora

3) Effective grid utilization by. S. Balser, S. Sankar, R. Miller, T. Curry, A.

Rawlins

4) A review on series compensation and its impact on performance of a

transmission line by Himanshu M. Joshi, Nshant H. Kothari

5) “High temperature conductors” A solution in uprating overhead lines by

R. Criado, I. Zamora, A. J. Mazon

6) Transmission line loadability improvement using FACT device by. R.

H. Besdadiya, C. R. Patel, R. M. Patel

7) Sag and tension calculations for overhead transmission lines at high

temperatures by. Mehran Keshavarzian, Charles H. Priebe

8) Maximizing the ratings of national grids existing transmission line using

high temperature-low sag conductors by M. J. Tunstall, S. P. Hoffmann

9) Statistical approach to thermal rating of overhead lines for power

transmission and distribution by. C. F. Price, R. R. Gibbon

10) Increasing the capacity of overhead lines in the 400KV Spanish

transmission network real time thermal ratings by. F. Soto, D. Alvira, L.

Martin

11) Determination of thermal rating and uprating methods for existing lines

by. R. Stephen, D. Muftic

12) Uprating of transmission capacity in great Riyadh 132 KV transmission

line grid system by adopting low sag and thermal rate up conductor by.

A. Kikuchi, R. Morimoto, K. Mito, Y. Kimura, A. Mikumo

13) Powering up a nation by Essel infraprojects limited. Ramnatt house

community centre, New Delhi.

- 63 -

7 Appendix

The overhead transmission line calculator is attached below.

Figure 19a. A figure showing overhead line rating calculator.

Figure 19b. A figure showing overhead line rating calculator.

- 64 -

The sag-tension calculator is attached below.

….

- 65 -

…

- 66 -

8 Abbreviations

KPLC- Kenya power and lightning company

IPP - Independent power producers

ROW- Right of Way

FACTS-Flexible alternating current transmission system

NERC- North American electric reliability corporation

HTLS- High temperature Low sag

SIL- Surge impedance loading

AAAC-All aluminium alloy conductor

ACAR-Aluminium conductor alloy reinforced

ACSR-Aluminium conductor steel reinforced

ACCC-Aluminium conductor composite core

ACCR-Aluminium conductor core reinforced

ACSS- Aluminium conductor steel supported

TACSR-Thermal resistant aluminium conductor steel reinforced

SQRT-Square root

Cct-Circuit

MW-Megawatt

KM-Kilometer

KV-Kilovolt

MVA-Megavolt-amperes

A.C. - Alternating current

D.C. - Direct current

Vs. - Versus

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