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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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ELECTRICITY SUPPLY DEVELOPMENT IN
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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ELECTRICITY SUPPLY DEVELOPMENT IN
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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ELECTRICITY SUPPLY DEVELOPMENT IN
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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ELECTRICITY SUPPLY DEVELOPMENT IN
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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ELECTRICITY SUPPLY DEVELOPMENT IN
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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ELECTRICITY SUPPLY DEVELOPMENT IN
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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ELECTRICITY SUPPLY DEVELOPMENT IN
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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ELECTRICITY SUPPLY DEVELOPMENT IN
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
TRANSMISSION SECTOR CONTND
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
TRANSMISSION SECTOR CONTND
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DEVELOPMENT IN THE
TRANSMISSION SECTOR CONTND
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
TRANSMISSION SECTOR CONTND
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
TRANSMISSION SECTOR CONTND
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
Strain/Tension/section Tower
(10 - 300) CCH CH DD30 SS30
Strain/Tension/section Tower
(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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