Modelling And Simulation Of The Impact Of Power Generation On The Distribution System

ABSTRACT

With the ever increasing demand of electricity consumption and the increasing in open access particularly in restructured (deregulated) environment, transmission line congestion is quite frequent. For maximum mitigation and benefit of this congestion, proper sizing and allocation of distributed generators (DG) are ardently necessary. A simple method is presented in this paper for the optimal placement and sizing of this type of generators in distribution electric power networks. A conventional iterative simple search technique combined with Newton Raphson (N-R) method of load flow study is applied on a real 15-bus distribution feeder model and on the standard IEEE 14-bus system. The Powerworld Simulator © v.15 commercial software have been used for the modelling, visualization, simulation and analysis of the power systems under study The objective of the formulation presented here is to lower down effectively both energy cost and power losses. The paper also employs an appropriate weighting factor in order to balance the cost and loss quantities, and at the same time to formulate the overall objectives leading to high potential benefit.

KEY WORDS

Power system, Modelling and simulation, Distributed generation, Newton Raphson, Objective function.

TABLE OF CONTENTS

COVER PAGE

TITLE PAGE

APPROVAL PAGE

DEDICATION

ACKNOWELDGEMENT

ABSTRACT

CHAPTER ONE

1.0      INTRODUCTION

1.1      Background of the project

• Problem statement
• Aim and objectives of the project
• Scope and limitations
• Project organisation

CHAPTER TWO

2.0            DISTRIBUTED GENERATION CONCEPT AND TECHNOLOGY

• Introduction
• Distributed Generation Concept
• Definition of Distributed Generation
• Distributed Generation Classifications
• Sierra Leone energy sector overview
• Reform of the Energy Sector

CHAPTER THREE

3.0     POWER SYSTEM MODELLING AND PROBLEM FORMULATION

3.1      Description of Distribution Networks under Study

3.2      Description of the Modelling Methodology

3.3             Modelling Implementation

• Objective Function

CHAPTER FOUR

4.0            SIMULATION RESULTS AND DISCUSSION

CHAPTER FIVE

• CONCLUSION And RECOMMENDATION

REFERENCES

CHAPTER ONE

1.0                                                      INTRODUCTION

1.1                                         BACKGROUND OF THE STUDY

Power systems were originally developed in the form of local generation supplying local demands, the individual systems being built and operated by independent companies (Jenkins et al., 2000). This is exemplified by the lighting of the Harbour Board of the City of Cape Town whose installation was commissioned on 3 October 1882, the lamps being supplied by generating plant installed in a building in St Andrew’s Square.   According to Palser (n.d), it is recorded that these lights “proved of great service, not only in minimising accidents, but also in facilitating the working of vessels at night”. During the early years of development, small generating station supplying local loads proved quite sufficient. In other words, the electric system was composed of multiple but isolated generation plants (Galli et al., 2011). For instance, initially 4000 individual electric utilities in the U.S. owned local grids and operated in isolation (Jin, 2010). However, it was soon recognised that an integrated system, planned and operated by a specific organisation, was needed to create an effective system that was both reasonably secure and economic (Jenkins et al., 2000). This in the view of EPRI (2000) means that centralised power systems evolved in the first place because of the various economic and reliability advantages associated with large-scale interconnected power systems.

Modern electrical power systems have developed over a period of about 70 years (Jenkins et al., 2010) based on economy of scale and efficiency. This is because modern society is very much dependent on the availability of cheap and reliable electricity (Bollen and Hassan, 2011) which warranted the replacement of small generating stations with large centralised generators. However, the economic and reliability advantages of 50 years ago may no longer apply today due to new technical and economic factors that have arisen in the past few decades (EPRI, 2000). In the view of Clark (2010) while some fossil fuels, like coal, are still cheap today, they are the major American and global atmospheric polluters. Therefore, if the human and environmental impacts of coal were calculated into its costs, then the real cost of coal energy generation for power would soar. The bulk of global electricity is generated in large (> 500 MW) power stations at around 20 kV (Freris and Infield, 2008). This is then stepped up by transformers to an extra high voltage (EHV) level such as 400 kV and carried by the transmission system to the bulk supply points, where it is stepped down to a high voltage (HV) level of around 100 kV. The 400 kV high voltage interconnected transmission network, according to Jenkins et al. (2010), is common in most of Europe and 750 kV in North America and China.

Although Sierra Leone is endowed with energy potential in various forms including biomass from agricultural wastes, hydro and solar power, it remains underutilized. Energy consumption is largely dominated by biomass sourced from fuelwood and accounts for around 80 percent of the energy used. Imported petroleum products, the next largest source of energy, are mainly for power generation and account for 13 percent of energy consumption. Only 15 percent of the total population and about 2.5 percent of the rural population currently have access to electricity. The power sector is small, with less than 150 MW of energy capacity connecting less than 150,000 customers with the cost for electricity heavily subsidized. The entire country lacks a stable and reliable public power supply and domestic demand remains significantly unmet.

The current electricity supply is challenged by generation capacity and seasonal variation and is disseminated using inadequate and aging transmission and distribution networks. It is delivered at a very high cost with Sierra Leone having one of the highest electricity tariffs in the sub-region. There are numerous waterfalls for hydropower and abundant sunlight for solar power generation with an estimated hydro project potential of more than 1000MW, while solar opportunities are above 240 MW. The major hydropower facility, Bumbuna Dam, with a peak of 50MW during the rainy season, has a reduced output of 8MW in the dry season.

The government has demonstrated a strong commitment to expanding the energy sector despite many major challenges over the past years. The enactment of relevant legislative reforms laid the foundation for the restructuring of the sector, which created the Electricity and Water Regulatory Commission (EWRC) in 2014, unbundled the former National Power Authority (NPA) into the Electricity Generation and Transmission Company (EGTC), and the Electricity Distribution and Supply Authority (EDSA) in 2015, and enabled the development of Independent Power Producers (IPP) projects. The EWRC focuses mainly on the regulatory aspects and set tariffs for consumers and tariffs between EGTC/IPPs, while the EGTC focuses on electricity generation and transmission. EDSA holds a monopoly as the single buyer from IPPs and the single seller to consumers.

Power Africa, a multi-partner initiative to increase efficient electricity in sub-Saharan Africa, supported Sierra Leone in 2015 with a $44.4 million four-year threshold program through the United States Millennium Challenge Corporation (MCC).  The program addressed:  strengthening the regulatory infrastructure; restructuring the water sector; streamlining the electricity sector; guiding the development of a roadmap for the implementation of reforms to enhance financial sustainability; and improved operational efficiency.  Other initiatives undertaken by the government include the establishment of a Rural Renewable Energy Project to support increased access to rural energy resources and a Rural Electricity Board and a Rural Electricity Fund to promote and make electrification widely available in all regions, a Renewable Energy Empowerment Project to develop a knowledge base of existing renewable energy policies. The Côte d’Ivoire-Liberia-Sierra Leone-Guinea (CLSG) interconnector project, under the West African Power Pool (WAPP) program, aims to provide an increased supply of electricity to these countries to meet the growing demand and will create an incentive for hydropower potentials that exist in Sierra Leone.

While the overall objective of the government has been to provide energy in sufficient quantities to all regions of the country, there has been an inadequate investment and limited private sector participation in the energy sector. The government has therefore embarked on various reforms focused on improving governance and regulation to encourage private sector participation in the sector. The national Electricity Act enables the participation of IPPs in power generation and distribution.  The Public-Private Partnership Unit in the Office of the President has developed a standard power purchase agreement to simplify and expedite negotiations with investors in energy and plans to establish feed-in tariffs to harmonize the sale of power from various IPPs into the WAPP and the national grid. The government is also providing special financial incentives to investors in the renewable energy sector and intends to promote the use of Liquified Natural Gas and Liquefied Petroleum Gas. The government is inviting private independent power producers to enter the sector and support the government in achieving this goal.

The International Energy Agency (IEA) defines energy security as the uninterrupted availability of energy sources at an affordable price (Miketa and Merven, 2013). Energy security has many aspects. Long-term investment is mainly linked to timely investments to supply energy in line with economic developments and environmental needs. Short-term energy security focuses on the ability of the energy system to react promptly to sudden changes in the supply-demand balance.

1.2      Problem statement

The connection of generation sources to distribution networks leads to a number of challenges because these circuits were designed to supply loads with power from the higher to the lower voltage circuits. According to Jenkins et al. (2010), conventional distribution networks are passive with few measurements and very limited active control. They are designed to accommodate all combinations of load with no action by the system operator. However, with significant penetration of distributed generation the power flows may become reversed and the distribution network will no longer be a passive circuit supplying loads but an active system with power flows and voltages determined by the generation as well as the loads. Ackermann et al. (2001) believe that this large variety of options for grid connection of distributed generation makes the analysis of grid integration issues very complex. Furthermore, that local network conditions have an important influence on the relevant integration issues. Hence, each network will require a detailed analysis. According to IEC (2010) it is a great challenge to interconnect renewable energy generation to power systems. Therefore, one important task of Smart Grid is to provide a dynamic platform for free and safe interconnection of renewable energy generation to power systems. This means that smart grid technology can address some of the problems of interconnecting DGs at the distribution level.

1.3      Aim and objectives of the study

The main aim of this research work is to conduct a study on the impacts of distributed generation. Therefore, this work aims at evaluating the potential effects of DG on the operation of electric power system with particular reference to the distribution system. Actualisation of this objective hinges on:

1. Extensive and intensive literature review,
2. Selection of appropriate simulation software,
3. Development of a distribution network model, and
4. Simulations to investigate DG

1.4                      Scope and Limitations

This research work focuses on modeling and simulating a power generation system on the distribution network. However, the crucial role of communication in electric power system will receive due attention while avoiding its modelling complexities.

1.5                      Thesis Organisation

This thesis is organised as follows:

Chapter 1 Introduction

Chapter 2 Distributed Generation Concept and Technology

Chapter 3 Modelling and Simulation

Chapter 4 results and discusion

Chapter 6 Conclusion and Recommendations