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GEP and TEP : Nigeria Power System
Master Thesis Project
February, 2012

Supervised by
Assistant professor Mohammad R. Hesamzadeh

Examined by:
Assistant professor Mikael Amelin

Electrical Power Division
School of electrical Engineering
Royal Institute of Technology (KTH)
Stockholm, Sweden.

To every Nigerian who longs for a day when Nigeria can boast of
uninterrupted power supply

ii

Acknowledgement
Firstly, I would like to thank my examiner, Mikael Amelin for accepting the masters’
thesis proposal and seeing a prospect in under going this project. I would also like to thank
my supervisor, Mohammad R. Hemsazadeh, who agreed to supervise the project and was very
helpful throught the period of carrying out this thesis Project.
Special thanks to Engr. Charles K. Nnajide and Engr Deji Ojo of the Power Holding
Company of Nigeria who assisted me in data collection. Without your help, the work would
have been next to impossible.
I cannot fail to thank my colleagues, Mahir Sarfati, Maria A. Noriega, John Laury, Olga
Galland for the amiable and friendly ambience of Bobenko room during the execution of
this project. It was fun sharing a work space with you all.
I cannot but thank these special people to me, Olayinka Irerua, Eric Okhiria, Olajumoke
Oke. These years in Sweden and at KTH would have been difficult without your support,
encouragement and love.
Very special thanks to my parents, Mr and Mrs Faleye, my siblings, Folake and Wuyi and
my family for your support throughout my studies. Blood is indeed thicker than water.
Finally, I want to thank God for his mercies and grace through out my life. Without You,
none of this would have ever happened.

iii

Abstract
The Nigerian power system is one plagued with incessant load shedding due to inadequate
generation and transmission capacities. Currently, less than 40% of the population is
connected to the national grid and less than 50% of the available installed capacity is actively
used in meeting demand. A new wave of energy reforms is on-going in the nation. There are
proposed generation and expansion plans. These reforms have only fully taken into
consideration present demands and not future energy demands. This means that even with
new plants and transmission lines being constructed; there may still be inefficient generation
and transmission capacities due to demand increase. This thesis models the uncertain future
demands in the integrated generation-transmission planning model. An optimal investment
plan is found using the deterministic optimization model of integrated generationtransmission planning. A decision analysis method was initially used to study the introduction
of uncertain demand into the deterministic model. Then, a two-stage stochastic model of the
generation-transmission planning taking into account uncertainties in energy demand is
developed using scenario-wise decomposition method. The demand was modelled as taking
discrete values with certain probabilities.
These models are mixed-integer linear programming problems. They are implemented in
the GAMS platform and solved using the CPLEX solver. A stylized version of the Nigerian
power system is developed and tested. A thorough analysis and comparison of results from
the models were carried out using the developed version of the Nigerian transmission grid.

iv

Table of Contents
Acknowlegement……………………………………………………………………………………………………...…iii
Abstract……………………………………………………………………………………………………………………...iv
List of tables……………………………………………………………………………………………………………….vi
List of figures…………………………………………………………………………………………………….………vii
1. Introduction......................................................................................................................... 1
1.1
Background ................................................................................................................ 1
1.2
Problem Definition and Objective.............................................................................. 2
1.3
Methodology and tools used ...................................................................................... 2
1.4
Report Overview ........................................................................................................ 3
2. Introduction to Generation-Transmission Expansion planning .......................................... 4
3. Basics of Optimization Theory ........................................................................................... 8
3.1.
Deterministic Linear Programming............................................................................ 8
3.2.
Stochastic Linear Programming ................................................................................. 8
3.2.1. Two-stage stochastic linear programming with recourse........................................... 8
4. Case study ......................................................................................................................... 10
4.1.
Background on the Nigerian Society ....................................................................... 10
4.2.
Overview of the Current Nigerian Power System.................................................... 12
4.3.
Data and Inputs......................................................................................................... 14
5. Models............................................................................................................................... 20
5.1.
Introduction .............................................................................................................. 20
5.2.
Deterministic Model................................................................................................. 20
5.3.
Scenario-based Decision analysis Model ................................................................. 21
5.4.
Stochastic Model ...................................................................................................... 22
5.5.
Simulation parameters.............................................................................................. 23
6. Simulation Results and Discussion ................................................................................... 25
6.1.
Individual Model Results ......................................................................................... 25
6.1.1. Deterministic Model................................................................................................. 25
6.1.2. Regret analysis ......................................................................................................... 32
6.1.3. Two-stage stochastic model ..................................................................................... 36
6.2.
Comparison of Deterministic and Stochastic results................................................ 43
7. Conclusions....................................................................................................................... 46
8. Future Work ...................................................................................................................... 47
References ................................................................................................................................ 48
Appendix I.................................................................................................................................. 1

v

List of tables
Table 1 Percentage cost component of a HV transmission line ................................................. 4
Table 2 Construction time(years) for different types of power plants ....................................... 5
Table 3 Power Generation capacity of the current Nigerian grid............................................. 12
Table 4 Generation capacity of proposed new plants .............................................................. 13
Table 5 Bus numbering of the network for this study .............................................................. 15
Table 6 Transmission Branch numbering for this study. ......................................................... 16
Table 7 Load/demand nodal distribution .............................................................................. 18
Table 8 Cost parameters used in the GAMS Model................................................................ 24
Table 9 Operation costs as used in the models......................................................................... 24
Table 10 Deterministic model: Power plant construction result, V ≥ 0 ................................... 25
Table 11 Deterministic Model: Transmission line construction results, V ≥ 0 ......................... 25
Table 12 Deterministic model: power plant construction result, V ≥ 1 ..................................... 27
Table 13 Deterministic Model: transmission line construction result, V ≥ 1 ............................ 28
Table 14 Deterministic model: Optimal Investment Costs comparison for compulsory and non
compulsory construction of new plants .................................................................................... 30
Table 15 Future demand for the regret analysis ....................................................................... 32
Table 16 power plant construction plan for regret analysis ..................................................... 33
Table 17 Generation in power plant for regret analysis ........................................................... 33
Table 18 Investment cost realization for regret analysis ......................................................... 34
Table 19 Regret in cost and served demand ............................................................................ 34
Table 20 Stochastic Model: power plant construction result, Vi ≥ 0 ...................................... 36
Table 21 Stochastic Model: transmission line construction results, Vi ≥ 0 ............................. 36
Table 22 Stochastic Model: Power plant construction result Vi ≥ 1 .......................................... 38
Table 23 Stochastic Model: Power line construction Vi ≥ 1 ..................................................... 39
Table 24 Cost comparison for the stochastic models ............................................................... 41
Table 25 Investment cost comparison for both deterministic and stochastic model. ............... 44
Table 26 Optimal network topology result ............................................................................. 45
i

i

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vi

List of Figures
Figure 1 Map of Nigeria showing population density.............................................................. 11
Figure 2 Map of Nigeria showing transmission grid layout.................................................... 11
Figure 3 One line diagram of the Nigerian transmission network showing existinglines(black
lines) and proposed new branches(pink lines) ......................................................................... 14
Figure 4 Deterministic Model :Power generation in power plants .......................................... 30
Figure 5 Deterministic model: Investment cost distribution ................................................... 31
Figure 6 Deterministic model: Network topology showing new line construction ................ 32
Figure 7 Regret calculated for demand .................................................................................... 35
Figure 8 Regret calculated for investment cost ........................................................................ 35
Figure 9 Stochastic Model :Average power generation in power plants ................................. 41
Figure 10 Stochastic Model: Investment cost distribution ....................................................... 42
Figure 11 Stochastic Model: network topology showing new line construction. .................... 42
Figure 12 Power plant construction variable for new plants for deterministic and stochastic
model. ....................................................................................................................................... 43
Figure 13 Power generation in new power plants for deterministic and stochastic model. .... 43
Figure 14 Cost comparisons of deterministic and stochastic model ........................................ 44

vii

1.
1.1

Introduction
Background

Electricity is very important to the social and economic development of any country. All
aspects of the life of the citizenry is affected by power supply, ranging from keeping a clean
home to running multinational companies. Without adequate power supply, businesses, homes
and the society at large cannot function to their full capacity. Goods and services would cost
more than they should if every business owner has to own a private generating unit; running a
home will be rigorous if there is no means of storing food due to non functional refrigerating
systems; health care provision would be substandard; unemployment would increase due to
fewer companies and these may lead to high crime rates; life will be boring if access to
entertainment is limited due to inadequate power supply. The electric power system of a
country should be built to meet the electricity demand of the citizens. Every household and
business office should have access to adequate power supply.
The problem of inadequate power supply can be tackled by generation upgrade and/or
expansion. This means that more generating units can be added to existing power plants or
new power plants can be built at new locations in a nation’s power grid. Additional generation
always result in increased power flow on transmission lines in the grid. If the existing
transmission network is not capable of transferring this added generation, then an upgrade or
expansion of the transmission system is also needed.
Any expansion planning involves determining where, when and how many new units must
be added to an existing system at lowest cost taking into consideration future demand values
[1]. Traditionally, transmission and generation expansion planning have been done
independently but in this thesis a simultaneous expansion plan is considered. In general,
expansion plans have been formulated to minimise investment cost of new units while
meeting technical and social constraints.
Since the number of transmission lines and generating units are integer values, an
expansion plan is a mixed integer problem. In addition, the planning can either be a one stage,
two-stage or a multistage problem [2],[3]. The planning problem is generally an optimisation
problem which can be solved using a variety of methods like those described in [4]-[6], [9].
When considering uncertainty in any of the parameters of an optimisation problem, the
problem becomes a stochastic optimisation problem. Stochastic optimisation problems are
classified into different categories such as those described in [7]-[9]. Based on the type of
stochastic problem, there exist different solution algorithms such as convex approximations,
stage wise decomposition and scenario wise decomposition to mention a few.
The Nigerian power system is currently suffering from inadequate generation and
transmission capacity. The demand is much higher than the generation and this has led to
constant load shedding and erratic power supply [11]. The installed generation capacity of the
Nigerian power system is currently estimated at 8800MW of which 25% is hydro and 75% is
gas fired thermal plants [12].

1

At present, only about 4200 MW is generated on the average compared to the installed
capacity. The Nigerian government is working on rural electrification and connection of more
consumers to the grid. To meet this growing demand, the government has given permission to
individual organizations to build thermal power plants. This means that the system is moving
from a vertically integrated electricity market structure to a more bilateral electricity market
structure.
The existing transmission network which currently consists of mostly 330 KV power lines
and a few 132 KV lines are weak with high energy losses close to 44% [14]. The network is
also mostly radial. The existing transmission system is not sufficient to transfer the additional
power injected to the grid by the new power plants.

1.2

Problem Definition and Objective

In this thesis, we consider the proposed generation expansion and suggest a few
transmission expansion paths for the Nigerian power grid. The proposed transmission
expansion paths were aimed at making the current network which is radial to become more
meshed. The expansion plans for both generation and transmission includes construction of
new power plants and transmission lines as well as upgrade of existing lines. This thesis
work aims to propose an expansion plan. In simple terms we aim to answer the following
questions:

Which of the proposed power plants should be built and how much power
should it produce?
• Which of the proposed new lines should be built and how many units?
• Which existing power lines should be upgraded?
It most be stated however that this study does not aim to solve all the power adequacy
problems of Nigeria or even propose a comprehensive generation/transmission investment
planning. The study aims to give suggestions on which power plants (i.e. The location in the
grid and their power capacity) and transmission lines the Nigerian government should be
planning to build. It also aims to provide a good basis for further in-depth study into the
problem of power supply and long term transmission and generation planning in Nigeria.

1.3

Methodology and tools used

Traditionally, generation and transmission planning has been done separately but in this
study, the generation and transmission expansion plan was modelled simultaneously to
consider their feasibility and necessity. A deterministic optimisation plan was modelled. The
deterministic model was run for two cases: an expansion plan where construction of all new
power plants is compulsory and an expansion plan where construction of all new power
plants is not compulsory. For both of these plans, the transmission network is considered for
both upgrade of old lines and expansion.
In addition, a two-stage stochastic model was developed. The changes expected in
demand over the coming years were modelled. The demand was modelled as an uncertain
parameter with discrete probabilistic distribution. The expected value of the objective
function and the generation and transmission plan for this case was optimized.

2


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