An Assessment of Embedded Power Generation in Nigeria
Chapter One
Aim/Objectives of the Study
This study aims at evaluating the impact of EG on the Nigeria Electricity Supply Industry.
Against this background, the specific objectives are:
- the determination of the impact of EG on the Nigerian power systemload flow using Newton-Raphsons’
- investigating the impact of EG on load factorand
- the degree of EG penetration on the Nigerian powersystem
- the effect of EG on the loading of network
CHAPTER TWO
LITERATURE REVIEW
Definition of Embedded Generation
Embedded Generation is viewed and defined in many ways. EG can be defined based on voltage level, proximity to customer load, by its primary mover or dispatch situation(s). Dolapo [20] quotes the Report of CIRED Working Group definition of EG in seven different countries thus;
In Australia, it is power connected to the distribution network (up to 132kV) which is capable of supplying customer load directly).
In France, it is power connected to the distribution network, capable of supplying customer loads directly.
In Germany, it is power used mainly for sun, wind and small hydro projects.
In Greece, it is power connected to the distribution system not centrally planned or dispatched.
In India, it is power from renewable energy sources (up to 11kV).
In Netherlands, it is power owned by utilities, industry or a combination thereof (up to 150kV).
In United Kingdom, it is power connected to a distribution system (up to 132kV).
In summary, Embedded Generation can be defined as a generation that is not centrally dispatched which is connected to a distribution network. This can be renewable (such as photovoltaic systems for distributed power supply, wind turbines etc) or conventional plants (like the Trans-Amadi Gas Turbine). This ties in with the International Council on Large Electric Systems’ (CIGRE) definition which Dondi et al[21] thus quotes- ―Distributed Generation as generation that is; not centrally planned, not centrally dispatched, usually connected to the distribution network and smaller than 50-100MW.‖ These are the four features of EG.
These definitions have left some important operational characteristics of EG like the ownership, penetration, power delivery etc in isolation as these features may not be assumed in general across board[22].
EG can be referred to as any or all of the following; Distributed Generation, Dispersed Generation, On-Site Generation, Decentralized Generation, Decentralized Energy, Distributed Energy etc.
From historical perspective, EG is not a new concept; it is basically viewed as the precursor to the presently popular electricity structure [23] and has become popular because of the global restructuring of the power sector as seen in the unbundling of the industry, the breaking of the generation monopoly with encouraged competition etc. The core reasons for investment in EG vary from one country to another. This is because developed countries like the USA (see table 2.1), Australia etc ventured into embedded generation as an effective way to defer costs in grid extension while improving the reliability of the already existing system infrastructure (with over 70% accessibility). In Nigeria, the recent investment in EG among other considerations is borne out of the power sector restructuring in response to the weak and limited national grid. There is therefore a need for a proper guide in Nigeria’s future investment in EG to counter a tendency of continued operation of EG being grossly limited by the general growth and development of the grid. This tendency arises because the present construction and operation of EG mainly targets high- income residential customers or small-scaled industrial users like the case of Trans Amadi station in Port Harcourt, Nigeria.
Due to the problems that are generally associated with the power system, EG has become a viable energy alternative (alternative to the traditional fossil fuels) not only for rural areas with characteristic high transmission and distribution costs but also for densely populated regions [22]. An exhaustive comparison between the embedded power systems and the central station generation and T&D power systems with focus on the network performance characteristics like voltage profile improvement, system losses, efficiency, power quality, operation and maintenance, fuel, emissions etc is presented in[24]- [25]. The ability of EG to have a positive effect on voltage profile improvement, system losses, efficiency, power quality etc depends on its optimal size, placement/location and number[26]–[30].
CHAPTER THREE
RESEARCH METHODOLOGY
A good network assessment cannot be done without a load flow study of the network. Load flow studies/programs give information of what happens at all the branches and buses (swing, generator or load) of the network:
- The active power,P
- The reactive power,Q
- The voltage magnitude,V
- The voltage angle, θ of the
- The direction of (1) and(2)
These are all required to know the general status of the network. After which the engineer can device means of improving the network where necessary.
Simplified Research Procedure
- Use a load flow method to access the network performance; voltage profile, power lossesetc
- Compute the penetration level of the EG to measure its effect on network loss
- Use load factor to determine the consumption efficiency of the network power.
Methods and Techniques Used
For load flow studies the following methods can be used:
(1) Gauss-Siedel Method (2) Newton-Raphson Method (3) Fast Decouple Method. Irrespective of the load flow study method used, the interest of the engineer lays in finding a good solution of the power network that meets convergence conditions.
Gauss Siedel Method
Gauss-Siedel Method is perhaps the oldest load flow method. It is a simple method that takes less computational time per iteration. It also requires a small computer memory and does not solve a matrix system.
This method also has a hand-full of limitations. It is best for networks with small number of buses. If has a slow rate of convergence and it therefore requires a large number of iterations. There is an increase in the number of iterations as the number of system buses increase. The speed of convergence is also affected by the choice swing bus. Furthermore, systems with heavily loaded lines, large number of radial lines, short and long lines ending on the same bus often do not converge with Gauss-Siedel Method. Its derivation and examples are in many power systems textbooks like[65],[66]etc.
Newton -Raphson Method
This method is based on Taylor series and partial derivatives. It is more sophisticated than the Gauss-Siedel Method. It takes less number of iteration to reach convergence and further takes less computational time. Newton’s method is more accurate and not sensitive to factors like choice of slack bus, and network size.
The challenges of this method are that each iteration process requires more calculation with a large computation time per iteration and obviously a larger computer memory than the Gauss-Siedel method.
Fast Decoupled Method
This is also known as fixed slope and Decoupled NR. It is a modification of NR. It takes less time per iteration but requires more iterations that the NR method. Its derivation is shown in [66].
CHAPTER FOUR
SIMULATION AND RESULTS ANALYSIS
Presentation of Results and Discussion
The results of the networks simulation studies for this research for the N-R load flow (with and without EG, compensation), load factor and the EG level of penetration are presented below;
CHAPTER FIVE
CONCLUSIONS
Research Findings
From the objectives of this study in Section 1.4 of Chapter One, the findings of this study include;
- From the load flow studies of the considered networks, EG has a good impact on the Nigerian power system as seen in its ability to reduce the network power losses and in its ability to improve the network voltage profile.
- This study on the Nigeria power network shows that the integration of EG and the installation of fixed shunt compensators can both improve the voltage profile of a network. However, the integration of EG to a network affects both the active and reactive power losses unlike with the installation of compensators where G-shunt affects only the reactive power and B-shunt affects only the active power loss. EG has a better impact than network compensators on general network
- EG unlike network compensators, reduces the loading of network elements especially the transformers’ loading. This is due to its connection at the distribution level
- The present EG level of penetration has a good impact on network loss reduction.
- For the given periods considered, the load factor margin for the month with the EG in service has a narrower margin than the month with the EG out of
These findings agree with some of the general advantages of EG as presented in Table 2.5.
Contribution to Knowledge
In recognition of other works done on the Nigerian power system, this work contributes significantly to knowledge in the following ways;
- It is the first work on the Nigerian network that compares the effect of EG with that of the traditional network compensators on the
- It is the first work on the Nigerian network that measures the effect of EG on load factor, to show the efficiency of consumers’ power utilization.
Conclusion
The introduction to this study identifies some of the various challenges of the Nigeria centralized power grid system with a brief history of the NESI that explains the role and great future of EG in Nigeria which necessitated this research to mitigate the power sector challenges for a general improved system performance.
The review considers the endearing general prospects and barriers of EG alongside its immediate pros and cons to the Nigerian power sector and shows how EG can help Nigeria mitigate some of the challenges of the power sector.
In this study also, the Siemens’ PSS/E software is used to run the Newton- Raphson load flow program to see the effect of EG on loss reduction and voltage profile improvement while comparing the results obtained with the installation of the traditional network compensators alongside their impact on network (element) loading. Furthermore, the load factor and EG level of penetration are determined via mathematical methods.
The integration of EG to the considered networks reduces active and reactive power loses by 7.09% and 10% respectively for the 28 bus network. A better active power loss reduction is achieved via the integration of EG to a distribution voltage level (i.e. from 9.97% to 5.51% on the PH Mains 132/33kV network). The integration of EG is good for networks with low voltages as it improves the general network voltage profile especially at the buses where it is directly connected ; buses 13 and 14 of the 28 bus network improved from 0.914 t0 1.02p.u. and from 0.937 to 1.02p.u respectively. Similarly, all buses within the PH Mains 132/33kV network with the exception of the Rumuodumaya improves to lay within the statutory voltage limit. More so, the integration of EG has a better effect on the general network performance than the installation of fixed shunt compensators have. The 14.76% penetration level of the EG is beautiful as seen in its impact on loss reduction. Attempts to further increase this level of penetration should be measured against its loss reduction capability so as to avert a possible increase in the network loss reduction caused by increased EG penetration. Finally, the load profile margin for margin for May 2014 (0.39-0.86) shows that consumers utilize power more efficiently with EG in-service than with EG out- of service as in May 2013 with a LF margin of 0.17-1.02.
Recommendations
- From simulation studies of the network, the future integration of the Trans Amadi gas turbine EG plant on the grid network would require the building and integration of a smaller size EG to be connected to the Jos and Kano buses of the grid to improve the voltage profile there and further reduce the general network loss among other
- Nigeria should invest in the power sector through the provision of EGs for local supply. Hence, the need to review the power sector reform
- Nigeria and other countries of the world with limited grid should invest more on EG with increased renewable energy regimes than on the extension of the limited/inaccessible
- System Planning, Operation and Expansion units should henceforth make allowance for the connection of future embedded
- Distribution companies should limit the maximum embedded generation capacity in a distribution feeder or connected to a distribution transformer between 25-50% of the feeder capacity so as to have a minimal power
- Incentives should be paid to distribution companies for voltage control so as to encourage their reactive power control practices/measures which EG can
- EG via biomass begs for imminent waste to energy investment to mitigate the power generation and waste management challenges of Nigeria and other developing countries of the world in
- Nigeria needs a Waste-to-Energy programme to enhance a more efficient use of her biomass potential like in the production of combustible liquid fuel (eg ethanol), biogas and other forms of electricity generation suitable for rural demands and for EG purposes in general.
- Policies alone are not enough; there is need for incentives from government to boost the installation of PVs in Nigeria. UK as mentioned in [54] has an incentive scheme for rewarding companies that connect their embedded generation plants to the
- Distribution companies across the federation should henceforth be encouraged to run load flows and invest in continuous research that will enhance better network growth and
Further Research.
As a continuation of this study, there is a need to also evaluate the impact of EG on the 28 bus network by carrying out fault analysis of the network with and with the EG. The subsequent studies from this can furthermore consider the impact of EG on the fault analysis of a section cut of the transmission network say, the PH Mains 132/33kV network.
More so, further studies should consider the determination of the maximum penetration level of the EG on the network that will have a good impact on the network operation ( good voltage profile and reduced power loss) to avoid attaining a penetration level above the maximum ―saturation point‖ where network loss will increase above the considered network(s) base case(s). The Plant Growth Simulation Algorithm method can be used for such studies after which the load flow results can be compared with the Newton Raphson and the Gauss-Siedel methods.
Learning Points
This work provided me a great opportunity to learn power system modeling and a greater opportunity to study and use the PSS/E software tool which enjoys a global exposure and usage for the modeling, drawings and simulations of the networks herein considered in this study.
References
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