A Technical Paper

8/10/2019 A Technical Paper

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Strengthening of High Voltage Transmission

Networks in Nigeria with the Introduction of

Multi-Circuit Towers.

A Technical Paper Presented

To

The Nigerian Institution of Electrical &

Electronics Engineers

(A Division Of NSE)

By

Engr. Salami, Adesina Jimoh (MNSE) Feb.

2014.


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Introduction

The theme of this paper is Strengthening of

High Voltage HV) Transmission Networks

in Nigeria with the introduction of HV multi-

circuit Towers

The new technology of multi-circuit in the

network was one of the solutions adopted

to combat part of the numerous challengesin the Transmission sector.


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Intro. Contnd

The issue of acquisition of Right of Way(ROW) for the

construction of new transmission lines has being a serious

problem, which most of the time resulted to undue delay of

project completion time or even a times marred completelythe accomplishment of the project. Though, this technology

has been in existence in some other well developed countries

long time ago, what we had in our network were HV single

circuit & double circuits until recently when we were

compelled to adopt the technology in solving the ROW

problem encountered in the construction of a new 330KV

double circuits lines that has to pass through a developed

town of Onitsha, in Anambra State.


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Itro.contnd

The estimate for compensation for structures andproperty ran to about N3Billion for about 4.75Km

length of the line and beside this huge sum there wthreat of litigations by not willing to let go owners oproperty along the proposed line. The operator of thnetwork, Transmission Company of Nigeria, assenteto the proposal brought forward to introduce a 5-cirHV towers into the system using an existing 132KV

line route. The solution was so timely because theproject was completed at a reasonable time and alssolved the menace of frequent system collapsingwhich was threatening the system as at the time.


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Business of electricity

supply involves: *Generation

*Transmission

*Distribution


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Business of electricity

supply contdFor a better understanding of the Power Industry in Nigeria, I

carried out a general over-view of the industry by giving its

history from the inception to the present day status.

Challenges that had militated against realization of the typeof an industry that is our collective dream, various solutions

that were proffered by the Governments to correct some

perceived anomalies in the operation of the industry, success

and failures that were recorded over time were enumerated.

And subsequently, the paper discussed the new development

in the HV transmission network which witnessed the

introduction of HV multi-circuit towers. Few design

parameters and extent of compliance to international

standard were given.


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ELECTRICITY SUPPLY DEVELOPMENT

IN NIGERIA:

The history of electricity supply development

in Nigeria can be traced to the end of the

19thcentury when the first generating

power plant was installed in the city ofLagos in 1898, fifteen years (15 years)

after its introduction in England, United

kingdom. The total capacity of the

generators used then was 60kw.


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ELECTRICITY SUPPLY DEVELOPMENT IN NIGERIA

CONTND

The Nigeria electricity supply company

(NESCO) commenced operations in the city

of Jos and its environs as an electric

utility company in 1929 with theconstruction of a hydro electric power

plant at kuru near Jos.

In 1946, Nigerian Government Electricityundertaking was established under the

jurisdiction of the public works department

(PWD) the take-over the responsibility of

electricity supply in Lagos.


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ELECTRICITY SUPPLY DEVELOPMENT IN

NIGERIA CONTND

Electricity supply management in Nigeria remained under

individual, municipal authority etc till 1950 when

Electricity Corporation of Nigeria (ECN) was established tomanage and co-ordinate electricity supply in Nigeria.

Niger Dam Authority (NDA) was established in 1962 with a

mandate to develop the hydropower potentials of the

country. ECN and NDA were merged in 1972 to formNational Electric Power Authority (NEPA) by decree. The

decree empowers NEPA to enjoy the monopoly of all

commercial electricity supply to the exclusion of all other

organizations.


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ELECTRICITY SUPPLY DEVELOPMENT

IN NIGERIA CONTND

Within this power conferred, Federal

Government of Nigeria through Federal

ministry of power (FMP) was responsible for

policy formulation and regulation; and throughNEPA, was responsible for operation and

investment in the management of electricity

supply in Nigeria. NEPA wholly owned sole

responsibility for power generation,transmission and distribution in Nigeria. There

were many reasons that necessitated the

establishment of NEPA, among them were:


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NIGERIA CONTND

*To vest the responsibility for the financialobligation on one organization

*Guarantee more effective utilization of

human, finance and other resourcesallocated to the electricity supply industry

throughout the country.


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NIGERIA CONTND

NEPA strived to meet ever-increasing electricity demand

of the nation but unfortunately their performance was

adjudged to be poor and the organization was ladened

with corrupt practices, ineptitude, insensitivity and all

other attributes of a failed system. Poor performance ofNEPA was undoubtedly a source of concern to the

Government. NEPA was confronted with issues of poor

operational and financial performances. Attempt to

address these issues of NEPA problems made the

Government of the day then to amend the prevailing

laws setting up NEPA (Electricity and NEPA acts) in

1998. The act was amended to remove NEPA monopoly

and encouraged private sector participation. With the

amendment in the act, NEPA ceased to have an

exclusive monopoly over electricity generation,

transmission and distribution & sales of electricity


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NIGERIA CONTND

But, in no distant time, the government discovered

that the desired results were not being gotten. It then

undone on the government of the day that a more

holistic approach is required thus, total overhauling

and reformation of the policy, legal and regulations

setting up NEPA was carried out.

Consequently, in the year 2001 amendments was made

in the act which then provides legal basis for theunbundling of NEPA, the formation of successor

companies and the privatization of the latter. This

gave birth to Power Holding Company of Nigeria

(PHCN) and its subsequent unbundling into 18

successors companies.


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NIGERIA CONTND

The Federal Government owned Electricity

company then comprises of the following:

Generation: 3 No. Hydro plants

7 No. Thermal Generating plants.


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NIGERIA CONTND

Worth of note is that, the total installed capacity of

the plants was 6,852MW and total available

capacity was 3542MW for a population of about 160

million (as at 31-07-2010)

Transmission: A radial transmission grid (330KV &

132KV) owned and managed by Transmission

company of Nigeria (TCN)

Distribution and sales: 11no. distribution

companies (33KV&11KV) which undertakes thewires, sales, billing & collection, customer care

services within each companys catchment area.


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ELECTRICITY SUPPLY DEVELOPMENT IN NIGERIA

CONTND

Strategically, the objectives of the reforms

are:

To transfer management and financing of

the unbundled companies to organized

private sector.

Establish an independent and effective

regulatory commission to oversee the

industry.

Focusing the Federal Government

attention on policy formulation and long

term developmental programme of the

industry.


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NIGERIA CONTND

Results expected from this holistic

transformation are;

Increased access to electricity

services

Improved efficiency, affordability,

reliability and quality services.

Greater investment into the sector

to stimulate economic growth.


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NIGERIA CONTND

In 2007, Bureau of public enterprises

commenced the privatization policy and by

30thSeptember 2013, PHCN ceased to

exist following a successful privatizationprocess by the federal Government.

The following listed tables are attached to

this report for a better appreciation of the

status of the utility company before itceased to exist.


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NIGERIA CONTND

Table 1 : Installed/Available

Generating capacity of the Nation

Table 2 : Power supply module

around the world.


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DEVELOPMENT IN THE

TRANSMISSION SECTOR:

Electric power transmission is the bulk

transfer of electric energy from the

generating plants by high voltage links

(wires) to transmission stations andSubstations and ensuring that, electricity

generated anywhere within the network can

be used to satisfy demand at any part of the

network. Whereas, electricity distribution ismainly concerned with the conveyance of

power to consumers by means of lower

voltage.


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DEVELOPMENT IN THE

TRANSMISSION SECTOR CONTND

Network formed by the very high voltage lines inthe network constitutes the interconnectivity

which is called super grid or simply, national grid.

Advantages of having system interconnectivity are

as follows;


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DEVELOPMENT IN THE


To achieve a more economical cost for a unit

of power generated.

To stabilize the network, thus making it more

reliable by providing spinning reserve at low

cost.

Guarantee a common frequency for the supply

within the net work.

Ensure continuity of electricity supply to all

over the system linked places irrespective of

behavior at a particular time of the localized

generating plant.


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DEVELOPMENT IN THE



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DEVELOPMENT IN THE


It could be seen from the module that,

the grid {operate at 400KV (Britain),

500KV(USA), 330KV (Nigeria) feeds asub Transmission stations (operate at

132KV ( Britain), 115KV (USA),

132KV(Nigeria)}. At this voltage level ,

sub-transmission , some less efficientgenerating plants feed into the network

and also, major consumers of electricity

supply are fed directly.


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DEVELOPMENT IN THE


Electricity supply is transmitted at high voltages(120KV and above) to reduce energy loss in longdistance transmission. Thus , the voltage magnitu

chosen for transmission are greatly influenced bygeography of the network. Very long transmissionlines require that the power should be transmittedhigh voltage. This is the situation found in the Nortand south America, Russia, China, India Etc. Powe

is transmitted at voltage level of 765KV in North aSouth America and efforts are on to increase thegrid voltage to 1000KV1500KV whereas ingeographically small country like Europe the lengtof network is smaller and the upper voltage level i

420KV.


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DEVELOPMENT IN THE


Power systems are universally high

voltage alternating current (HVac)

and the use of high voltage directcurrent (HVdc) technology which is

of better efficiency is mainly

employed for specialized purposes

such as extralong distancetransmission lines or in submarine

power cable because of high cost of

the conversion equipment.


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OVERHEAD TRANSMISSION LINES:

Overhead lines are mostly used for the power

transmission on the ground of economy because,

major part of insulation is provided by air which

cost relatively zero naira. In a constrainedenvironments such as urban areas, underground

cables are used for high voltage transmission, the

cost is about 10 times that of high voltage

overhead lines though, the ratio decreases withlower voltages. The difference in the cost arose

from the cost of providing insulation. Overhead

lines conductor(s) are suspended from insulators

which are themselves supported by towers.


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DESIGN OF OVERHEAD TRANSMISSION

LINES

Primary considerations in the design

of transmission lines are;

Determination of line length Grid voltage

Line conductor size

Tower structure Allowable sag on the line

Tower span length


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DESIGN OF OVERHEAD

TRANSMISSION LINES contnd

Grid voltage: The voltage level of the

grid is determined based on the

length of the network. The reasonbeing that, power loss is recorded

along the line. Therefore to maintain

allowable power loss which is based

on the percentage of the declaredvoltage ( 6%) the grid voltage

magnitude is proportional to the line

length.


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DESIGN OF OVERHEAD

TRANSMISSION LINES contnd

Conductor size:

Powerloss = I2R .. (1)

R = L/a . (2)

- coeffient of expansion- Line length

- Conductor cross sectional area.

In equation 2

R L/a

Bundled conductors ,thats a more than 1 conductor per phaseline are used to reduce line reactances, corona loss & radio

interference and conductor voltage gradient.


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DESIGN OF OVERHEAD TRANSMISSION LINES contnd

3. Line Insulation:

The insulators provide adequate leakage path from

conductor to earth .

Pin type insulator are used for line voltage up to 33KVwhile suspension/ tensioning strings are used for line

voltage above 33KV. This consist of string of inter

linking separate discs made of glass, or porcelain or

silicon.

Number of discs in the string depend upon the linevoltage (11No for 132KV, 18No. for 330KV)


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DESIGN OF OVERHEAD TRANSMISSION

LINES contnd

Towers:

There are two main types of HV Towers.

Those for straight runs called suspension

towers in which stress due to weight of the

line conductors and string insulators has to be

withstood.

Those for changes in route called deviation

towers (angle towers). This withstands theresultant forces set up when the line changes

direction in addition to weight of the line

conductor and string insulators.


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Contnd

TYPES OF TOWERS. 330kv 132kv

DC SC DC SC

Suspension towers (0 - 20) AAH AH DD2 SS2

Strain/Tension/section Tower

(0 - 100) BBH BH DD10 SS10


(10 - 300) CCH CH DD30 SS30


(30- 600) DDH DH DD60 SS60

Dead End Tower (60 - 900) EEH EH DD90

SS90


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Contnd

Other general considerations in

design of tower are

Extra forces resulting from abreak in the lines on one side of

the tower ( Uplift force)

Nature of the conductor surface( e.g. effect of ice, dust)

Wind loading


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Contnd

Allowable Sag on the Line.

This is subject to Standard Specification

for electrical clearance and

characteristics of the conductor. The value

of sag determines the tower height, towers

span.

Tower span length is the distance between2 steel towers ( lattice) which on high-

voltage lines (330KV) are in the range of

370m-470m and the tower height is about

45m for 2X330KV lines.


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Design Criteria

Initial and final sag is

calculated for each ruling span

without exceeding the tensionlimit specified below:


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Contnd

Loading Condition Tension limit

ACSR unloaded

Initial, 10 30%

Final, 10 overland 25%

Final, 10 18%

Open bodies of water

ACSR loaded

Final, 10 60%


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Contnd

Tension limits are given as a percentage of the

conductor ultimate tensile strength calculated in

accordance with IEC 61089.

Vertical Clearances specified are based onmaximum line conductor sag at 75

330KV 132KV


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Contnd

Vertical Distances

Normal ground 8.0 6.7

Road crossing 9.0 8.3

Buildings, poles, structures, walls,

And cradle guards. 5.2 5.0

Limited access motorways and

dual carriage ways. 10.0 10.0

Navigable waterways (at high water level) 15.0 15.0

Pipelines (oil, gas, water). 10.0 10.0

Communication and power line wires 4.6 3.6 Cradle guard to top of railway track 9. 8.3


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Contnd

Horizontal Distances

Nearest steel of transmission tower to

Edge of navigable waterways,pipesline,

Bridges, highways, pavement, railway

(nearest rail), buildings on right-of-way

And at crossing, to structure of line being

Crossed 50.0 50.0


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Documents

A Technical Paper