ABSTRACT
ACKNOWLEDGMENTS
LIST OF FIGURES
LIST OF TABLES
LIST OF ABBREVIATIONS
LIST OF SYMBOLS
CHAPTER 1: INTRODUCTION
1.1 Project Background
1.2 Upper Karnali Hydropower Project (UKHPP)
1.3 Research Questions
1.4 Research Objectives
1.5 Research Approaches
1.5.1 Phase One
1.5.2 Phase Two
1.6 Scope and Limitations of the Thesis
CHAPTER 2: FUNDAMENTALS OF DISTRIBUTION SYSTEMS
2.1 Types of Distribution Systems
2.1.1 Classification based on nature of current
2.1.2 Classification based on construction
2.1.3 Classification based on the arrangement
CHAPTER 3: SELECTION OF OPTIMAL DISTRIBUTION SYSTEM
3.1 Required Data and Assumptions
3.2 Selection of Load Center and Grid Network
3.3 Selection of Grid Network
3.3.1 Algorithm for Kruskal’s algorithm
3.3.2 Flow Chart for Kruskal’s algorithm
3.4 Optimized Grid Network
3.5 Voltage level Selection
3.6 Conductor Selection
CHAPTER 4: LOAD FLOW ANALYSIS OF DISTRIBUTION SYSTEM
4.1 Mathematical Background
4.2 Solution Algorithm and Flow Chart
CHAPTER 5: SIMULATION RESULTS
5.1 Load Flow Analysis Results
5.2 Results Summary
5.3 Sensitivity Analysis
CHAPTER 6: VERIFICATION OF RESULTS
6.1 PSAT Simulink
6.2 Standard 33-bus Radial Feeder System & f/b Sweep based Algorithm
CHAPTER 7: ALTERNATIVE SOLUTION
7.1 Identify the remaining alternative sources and connect into the grid network ...
7.1.1 Central Generation of Energy
7.1.2 Distributed Generation of Energy
7.2 Electrify limited area on the basis of priority
CHAPTER 8: COST ESTIMATION
CHAPTER 9: CONCLUSION AND RECOMMENDATION
REFERENCES
ANNEX
Annex 1: Research Paper Publications
Annex 2: Location of Different Buses and number of household
Annex 3: Way selection with least distance
Annex 4: Load Flow Result by using Newton Raphson Method (200 kW)
Bus Voltage and Load Power
Line Current, Power and Losses
Annex 5: Load Flow Result by using Sweep Forward/Backward Method
Bus Voltage and Load Power
Line Current, Power and Losses
Annex 6: Load Flow Result by using Newton Raphson Method (400 kW)
Bus Voltage and Load Power
Line Current, Power and Losses
Annex 7: MATLAB Coding
This study illustrates the best approach for energy access to the affected area of a 900 MW Upper Karnali Hydropower Project (UKHPP) located in Western Nepal. As per concession agreement executed between the developer of UKHPP and the Government of Nepal, the developer will develop 2 MW power plant at the toe of the dam using the environmental release discharge to electrify the affected area of UKHPP. First, the study looks at the optimization of the electric grid network in the project affected area, using Kruskal’s algorithm. The optimization is carried out so that access to electricity is guaranteed to possible load centers in the affected area to the extent possible in technical and financial feasible manner. This study is an attempt to connect the possible load centers through an optimum network design based on demography, topography, technical feasibility and socio-economic factors. The study focuses on the design of the electrical network based on a least distance path between the identified nodes. The designed network is based on the survey using GIS, Topographical maps, and satellite views from Google map. A total of 57 load centers are identified connected through a grid 144.59 km in length. Similarly, taking n=4 sample, the total length of 220V distribution system is estimated to be 417.24 km.
After that, the study focuses on the Static Load Flow Analysis (SLFA) by developing a framework based on Conventional Newton- Raphson method to analyze the network’s parameters. The result obtained from the analysis is compared with the results of standard 33-bus radial feeder system and forward/backwards (f/b) sweep based algorithm using statistical analysis. The standard error is accepted for the 95% level of significance. It is concluded that, the load flow analysis (LFA) of the primary distribution in this study conducted using the N-R method was adequate and best fit for a grid-like network with medium voltage level. The estimated losses are low and under the limit (i.e. 2.04%) which shows that the designed system performs adequately. From the analysis, it is found that, the pre-defined generation of 2 MW power is insufficient to electrify the whole affected area of the UKHPP. Different alternative ways are recommended to manage the load and provide electricity to the people of the affected area.
This Graduate thesis has been conducted as a project study and was supported by Office of the Investment Board (IBN), Governmental of Nepal. So, first of all I would like to acknowledge the IBN and IBN’s team, who believed in me and provided me with the opportunity to work with them.
I would also like to thank my supervisor Mr. Shailendra Kumar Jha, Assistant Professor, Department of Electrical and Electronics Engineering, School of Engineering, Kathmandu University for his great guidance and supervision. I would like to thank him for being the best supervisor, providing a supportive environment and advice.
In addition, I would like to thank my supervisor Dr. Nicholas Christofides, Assistant Professor, Department of Electrical Engineering, Frederick University for his great guidance and supervision. I would like to thank him for his supportive environment and advice at Frederick University, Cyprus.
Taking the opportunity, I would also like to thank my co-supervisor Mr. Bidur Raj Gautam, Consultant Transmission Engineer, Office of Investment Board, Government of Nepal for his guidance and supervision.
Many thanks also go to my co-supervisor Mr. Bibhu Bikram Shah, Consultant Manager, Hydro Project, Office of Investment Board, Government of Nepal for his guidance and support.
Lastly, I would like to thank Dr. Hari Neopane, Head of Department and Associate Professor, Department of Mechanical Engineering, School of Engineering, Kathmandu University for his support and suggestions during my thesis time and degree period.
Several people have been helpful throughout the various stages of this study, whether through software interface discussion, technical ideas, technical supports, and simply with their motivation and encouragement. Especially, I would like to acknowledge Mr. Nawaraj Chapaguai, Mr. Rojesh Dahal, Mr. Dipendra Jee Mandal, Javed Hasan Noor, my class mates Ramesh Maharjan, Kshitiz Khanal and Ajay Singh.
Also, I would like to thank all the staff of Kathmandu University, Frederick University and Office of Investment Board, Government of Nepal who helped me overcome several technical, social and psychological problems that I faced while doing my research work.
Finally, I am obliged to my parents, who believed in me and encouraged me to do my best. They have been my center of strength.
Figure 1: Administrative Map of Nepal
Figure 2: Typical electrical system[9]
Figure 3: Overhead Transmission and Distribution System[11]
Figure 4: Underground Distribution System[11]
Figure 5: Radial Power Distribution System
Figure 6: Loop Power Distribution System
Figure 7: Network Power Distribution System
Figure 8: Flow Chart
Figure 9: Optimum Grid Network (i)
Figure 10: Optimum Grid Network (ii)
Figure 11: Flow chart
Figure 12: Distance vs. Voltage (pu) at Linear and Real Network Structures
Figure 13: Distance vs. Cumulative Power Losses at Linear Network Structure
Figure 14: Cumulative PLoss and QLoss per km at Real Network Structure
Figure 15: Active and Reactive Losses with the variation of Current at Real Network Structure
Figure 16: PSAT Circuit diagram
Figure 17: Nose curves
Figure 18: Block Diagram for Central Generation of Energy
Figure 19: Block Diagram for Distributed Generation System
Figure 20: Optimized grid for electrify limited area on the basis of priority
Figure 21: Optimized network for the case with cross exchange transmission line
Table 1: Project Issues and Approaches
Table 2: Economic Voltage Selection
Table 3: Conductors with their Parameters[26]
Table 4: Conductor Selection for Different Network
Table 5: Sensitivity Analysis
Table 6: Comparative result of different Load Flow Algorithms (Paired Sample T test)
Table 7: Sensitivity Analysis for case 2
Table 8: Economic Voltage Selection for case 2
Table 9: Conductor Selection for different Network
Table 10: Equipment with their cost
Abbildung in dieser Leseprobe nicht enthalten
Abbildung in dieser Leseprobe nicht enthalten
Nepal is a mountainous country having huge economically and financially feasible hydroelectric potential up to 42,000 MW[1]. But, due to lack of hydroelectricity development and poor implementation, only 76 % of people are in access of electricity with 128 kWh electricity consumption per capita[2] [3]. The share of renewables is 12% and consists of solar, wind and micro hydro[4]. Even in the places connected with grid, load shedding occurs up to 12 hours a day in winter and 2-4 hours a day in wet season[5]. In 2013/14 the annual peak power of Integrated Nepal Power System (INPS) was estimated to be 1201 MW, with the estimated shed being 410 MW[5]. Although, the potential is very high, the power generation could not fulfil the demand. Thus, the hydro electricity generation should be accelerated with positive ideas, plans, technologies and implementation work. According to the various study, it was found that, the reason of low energy consumption per capita of Nepal is due to unavailability of access to energy in rural areas and because of the small number of industries with in the country. Only 1.47 % are of industrial consumer type in Nepal[5].Similarly, around 83 % of people are in rural area, where the energy access percentage is only 60 %[6] [7].
Currently, there are numerous organizations working in the energy sector, aiming to increase the energy generation, energy access and the energy consumption per capita. Organizations like Alternative Energy Promotion Center (AEPC) focuses in renewable energy for rural and urban areas, providing energy access and socio-economic development of people. Similarly, GoN provides new ideas and laws to increase the rate of energy access and support the public in socio-economic, technological and networking improvement. Under GoN, two organizations; Office of Investment Board Nepal (IBN) and Citizen Investment Trust (CIT) are working to provide funds and manage the implementation of big projects. Similarly, different Acts and policies are defined for development of hydropower and others parameters of the nation from different aspects.
The potential of hydroelectricity is very high, but untapped. So to generate the electricity at low cost by utilizing the local resource, to extend reliable and qualitative electric service, to tie-up electrification with the economic activities, and to develop hydropower as an exportable commodity, the GoN had presented a Hydropower Development Policy in 2001. It has become important in this context that the hydropower policy should clearly reflect the issues such as development of multipurpose plans for maximum utilization of the available water resources, suitable sharing of benefits, role of public and private sector, utilization of internal as well as external market, and clarity and limpidity in activities of GoN with the private sector, etc.
According to the Hydropower Development Policy, the rural electrification shall be expanded to provide energy access to as many people as possible, and encouraged by operating mini projects at the specific location. In case of the nearby area of a hydro project, rural electrification shall be encouraged to be developed by the hydro project. One percentage of the royalty obtained by the GoN from the hydro project shall be provided to the Village Development Committees (VDCs) aimed for expansion of rural electrification[8].
Awarded in 2008 to GMR-ITD consortium the UKHPP is one of the most ambitious projects in Nepal with an installed capacity of 900 MW. It is a peaking ROR type project. The project is located in the western regions of Nepal and affects twelve VDCs of Surkhet, Dailekh and Achham districts. Figure 1 shows the administrative map of Nepal, where the location of UKHPP is highlighted. The project area is located in a hilly region of the country, where the location of proposed nodes occurred from (28°43'49.14"N) to (29° 1'13.87"N) in south north direction, (81°22'37.57"E) to (81°36'9.96"E) in east west direction, with altitude variation from 494 m of sea level to 1976 m. The project area is unique in itself and has its own characteristics defined by steep hills, river crossings, forest and frequent altitude variation. Total land acquisition or land to be leased is estimated to be 282.56 Hectares (46.8 Hectare private and 235.76 Hectare Governmental). The project displaces 56 households from the project affected area.
Abbildung in dieser Leseprobe nicht enthalten
Figure 1: Administrative Map of Nepal
In 2011, there were 10,502 households in the 12 VDCs. Among them, only 88 households were connected with electricity supply through local micro hydro power plants. Other households used different alternatives such as kerosene, bio gas, solar etc. as lighting source. As by Hydropower Development Policy and social responsibility, the project shall be encouraged to provide energy access to at least these 12 VDCs [6, 7]. As per the concession agreement executed between the Government of Nepal and the developers of the UKHPP a 2 MW hydro power plant at the toe of the dam dedicated for the electrification of the affected area is planned.
This study aims at addressing the following research questions:
1. What will be the maximum demand?
2. How to determine the capacity?
3. How to electrify the affected area?
4. How to operate the system in balanced and efficient condition?
The first and second questions provide the total capacity of generation that is required to electrify the whole area. The peak demand and the methodology to calculate it are identified. The third question is about the load map, optimum voltage level and different components required in the system. Similarly, the fourth question gives the idea about the characteristics of the system. The satisfaction of the designed grid and their existence was carried out with the help of load flow analysis.
The main objective of this study is the design, development and evaluation of a model for an energy access system under that benefits the affected area of Upper Karnali hydro project.
The study will have to deal with three main challenges:
1. Identify the optimum electric distribution system.
2. Perform load flow analysis to identify the characteristics.
To fulfill the objectives of this research, following lists of approaches are identified.
- Literature Review
- Data Collection
- Primary Data
- Secondary Data
- Desk Research
- Field Research
- Software Interface
- System Modelling
- Model Verification
- Model Optimization
- Analysis
- Results Verification
- Decision
Table 1: Project Issues and Approaches
Abbildung in dieser Leseprobe nicht enthalten
Table 1 presents the main issues and how they were methodically approached. The issues were resolved in three different sections. First, the affected area is identified with the help of Google Map, GIS and field visit. Since the area is to be electrified, different approaches to load mapping and electrification were identified. Then, for the best one of the options, load flow analysis will performed, which is the second objective. Modelling and design is performed in MATLAB. After completing the load flow analysis, optimized the system is identified so that, the system will be technically and financially feasible. The detailed methodology is described in chapter 3 and 4.
In order to address the raised questions and fulfil the objectives, this study was conducted in two phases at different institutions. The first phase was completed at School of Engineering, Kathmandu University with direct cooperation of Office of the Investment Board, Government of Nepal. The second phase was completed at Department of Electrical Engineering, Frederick University, Cyprus. The detail works conducted in two different phases is explained below:
The phase one was conducted at School of Engineering, Kathmandu University and Office of the Investment Board, Government of Nepal. This phase includes the Discussion with stakeholders, Problem Identifications, Information Collection, Data collection, Literature Review, Objectives Setting, Approaches and Method Development, Proposal writing and defense etc. A discussion program within the Office of the Investment Board was conducted from where the information regarding project area and tentative objectives were obtained. The problem related with the project were identified through the discussion with stakeholders, literature review and interaction program. The aim of the literature review was to get the idea regarding the project and the approaches that used in earlier related studies. Based on the problem identified, related research questions, objectives and their solving methodology were set. Proposal writing and defense were included in this phase. In addition, the works related with the 1st objective was completed within this phase.
The phase two was conducted at Department of Electrical Engineering, Frederick University, Cyprus. This phase includes the completion of 2nd objective, Thesis writing and finalization. A framework was developed for load flow analysis of distribution system and the data, information available from 1st phase were used. Phase two was completely focused on the research and documents task.
This study focuses on the development of an optimized electric primary distribution system for energy access to UKHPP affected area. The demographic parameters of 2011 were taken as reference value, where no demographic analysis was performed. After developing the model, some assumptions were considered for further analysis. The analysis for load flow was static considering tire 3 categories. So, it can be used for planning prospect, but not for operation management.
Distribution system is the line connecting step down transformer and load center, and is used to distribute the power from load transformer to the consumers. It serves as the network from the distribution center to the load center. It is a very important part in electrical system since it is the main portion that link bulk power to the consumer. The figure given below shows the typical electrical system:
Abbildung in dieser Leseprobe nicht enthalten
Figure 2: Typical electrical system[9]
Figure 2 above shows a single line diagram of a typical electrical system. The power generation is generated at a voltage level of 11 to 33 kV. The power generated is stepped up with help of step up transformers and transferred to the transmission line. The transmission system is basically a bulk power transfer line between power generating station and the distribution station. There may be different levels of transmission systems depending on the type of transmission for example, primary or secondary transmission. It may include sub-transmission line with intermediate voltage level as per requirements. The transmission system contains step-up and step-down transformers at the generating and distribution station, and the conductors connecting them. Primary distribution system is the part which operates at voltages somewhat higher than general utilization and handles high electrical load[10]. Similarly, the secondary distribution system is the link that directly connects the consumers with utilization voltage level.
In detail, the primary distribution system is that part of the distribution system that lies between the main distribution substation and the utilization transformers. The voltage of transmission line is stepped down to the lower voltage level by using step down transformer at distribution substation. In case of Nepal, the primary distribution system is found to have the voltage level of 3.3 kV, 6.6 kV, 11 kV, 22 kV or 33 kV. This type of distribution system is usually used to deliver the electric power in large industries and specific areas by using dedicated feeder lines. Since the voltage level of primary distribution is higher than secondary distribution system, it has lower distribution losses according to ohm’s law. The primary distribution has many advantages over secondary, so that the consumers with higher demand have priority to the primary distribution system. In primary distribution system, different arrangements such as; Radial type, Loop type, Interconnected Network System and Parallel System are used considering the characteristics of the specific arrangements. The detail descriptions of the arrangements are explained in chapter 2.1.
On the other hand, secondary distribution system is the portion of electrical system that connects utilization transformer and load center. The voltage level of primary distribution system is further stepped down to the utilization level with the help of utilization transformer and supplies to the consumer. In case of Nepal, the secondary distribution is found to have the voltage level of 230V in single phase system and 400 V in 3 phase system. Since the voltage level of secondary distribution system is low and can be directly used in households, huge technical and non- technical losses occur. Generally it is of radial type and distributed through overhead as well as underground.
There are different schemes of distribution system or simply called sub transmission line. Each of these systems has their own specific advantages and disadvantages. It can be classified based on different parameters. Some of the important classifications are given below:
a) AC Distribution System
In present context, the generation, transmission and distribution of electrical system is popular in the form of alternating current. It is due to the nature of alternating current to be stepped up or stepped down. The voltage level of electrical system can be changed with the help of transformer. Generally, the AC distribution system is very popular in generation, distribution and medium voltage level transmission system. Further it can be distinguished into two parts;
- Primary Distribution System
- Secondary Distribution System
b) DC Distribution System
For specific applications, DC supply is very important. For example, DC supply is required to operate variable speed machines. Similarly, it finds application in electro-chemical works. For this purpose, AC supply is converted into DC using transformer at substation, then supplied through DC distribution system to consumer. This distribution system is further distinguished into two parts;
- 2-wire DC system
- 3-wire DC system
a) Overhead Distribution System
Figure 3 below shows the overhead transmission and distribution system of an electrical power system. In this type of distribution system, the power is supplied with the help of overhead conductors. The conductors are supported by steel or wood or concrete towers and pole. Normally, the type of tower material is selected based on the territory, topographical, environmental and economic factor. This is the simplest type of distribution system, generally used in low density area such as rural area.
Abbildung in dieser Leseprobe nicht enthalten
Figure 3: Overhead Transmission and Distribution System[11]
There are some advantages and disadvantages of overhead distribution lines such as; Advantages:
- Low Cost
- Better heat dissipation
- Easy to identify the fault
- Easy to installation, maintenance and repair
- Can be used in high voltage level
Disadvantages:
- Overhead distribution system is exposed to the elements
- Can be affected by human and natural phenomenon
- High technical and non-technical losses
- Problem in right-of-way
- Effect on esthetical factor
b) Underground Distribution System
This type of distribution is used in urban areas where the total distance is short with dense population. The cost is comparatively high than overhead distribution system. Generally, the conductors pass through pipe network placed under ground. Figure 4 below shows the underground distribution system. There are manholes placed at certain distance, from where the connections can be done. Generally, the utilization transformer and the switch yard are placed at the manhole.
Abbildung in dieser Leseprobe nicht enthalten
Figure 4: Underground Distribution System[11]
Advantages:
- Esthetically preferable
- Requires smaller right-of-way
- Fewer problems with vegetation, automobile accidents, lighting, or vandalism
Disadvantages:
- Costlier
- Difficult to identify the fault
- Difficult to Installation, Maintenance and Repair
- Difficult when passing through geographic obstructions such as hills,
marshes and river
- Potential risk from careless digging
- Problem in heat dissipation
- High insulation is required
- Difficult to use above medium level voltage.
a) Radial Power Distribution System
Radial power distribution system is the simplest type since the power is fed from single unit. Figure 5 below shows the block diagram of the radial structured distribution system. The generation at generating point is supplied through radial lines, which may extend to the various areas. It is very simple in installation and operation. So, the cost is very low and basically used in remote areas. This system is the least reliable in terms of continuity since there is absence of backup.
Abbildung in dieser Leseprobe nicht enthalten
Figure 5: Radial Power Distribution System
b) Loop Power Distribution System
Loop Power Distribution System is more flexible than the previous one. Figure 6 below shows the basic block diagram of the Loop Distribution System. Due to the presence of a few alternative connections, it is considered to be more reliable than radial system. It is expensive and complex in compare with radial structure. It is generally used in urban area and industrial area, where the reliability plays significant role.
Abbildung in dieser Leseprobe nicht enthalten
Figure 6: Loop Power Distribution System
c) Network Power Distribution System
Figure below 7 shows the basic block diagram of Network Distribution System. It is the combination of radial and loop distribution system. All of the loads are directly connected with the distribution station. It is very popular where reliability matters. But is very expensive and advanced to install and operate. Generally, this type of distribution system is used in highly sensitive areas, where the reliability is most important.
Abbildung in dieser Leseprobe nicht enthalten
Figure 7: Network Power Distribution System
Like different types of distribution systems, there are numerous computational techniques and algorithms such as; breadth-first search, depth-first search and minimum tree spanning algorithms. These techniques and algorithms are used to develop and elaborate the basic graph searching, and get an optimized network for the network analysis and further development[12]. But it is more important to select the best distribution type so that more accurate and efficient result will be obtained. It does not matter, how many techniques are there, but it’s very important to select best one, so that technical, financial and social acceptance is satisfied[13].
Kruskal’s, Prim’s, Reverse-delete and Boruvka’s algorithms are some of the algorithms based on tree spanning principle[14]. Kruskal’s algorithm was used in various research to find the optimized network of electricity distribution, telephone network line, forest’s tree management, multicast routing, road planning etc.[15] [16] [17] [18] [19] [20]. It is a minimum-spanning-tree algorithm where the algorithm finds a branch of least possible weight that connects any two nodes or point in the given system. It is a greedy algorithm in graph theory which used to select the least distanced branch, forming a complete network with possible minimum length[21].
Similarly, an optimizing tool called Network Planner tool for electrification planning was found to be used in different researches [20, 22, 23, 24]. It is a decision support tool for exploring cost of different electrification technologies derived by technical, social, economic and geological factors. This tool should be able to consider different type of renewable energy system in mini-grid option[22].
The best fit grid option was selected after computation of large volume of data. The list of required data is given below:
A)Geospatial Data : The spatial location of the settlement and project area were taken from an online survey with the help of topographical map, GIS and Google map. The importance of spatial location is to identify the settlement area and their quantity for proper design and analysis of the grid system.
B)Demographic Data : It includes the population characteristics, such as total population, population density, growth rate, mean household size etc. For referenced value, the Governmental Data of 2011 (CBS-2011) was used.
C) Electricity Demand: Unique geographic location, territory, altitude, and political states make it difficult to generalize the energy access status and their potential electrical demand. Especially in the un-electrified area, it is difficult to guess and generalize the load pattern and demand. The tentative demand is required during selection of conductors, transformers and other parameters so that no problems will occur in future. So, the household of affected area are assumed to be under tire 3 category (i.e. minimum 200 W load demand, minimum 1 kWh consumption per day, minimum 8 hours availability duration per day and minimum 3 hours per evening). In this study, the electricity demand was considered as a dummy load for each household. The power demand per household was considered to be same.
In planning of distribution system, first the nodes (or Load Centers) were identified, so that the whole area would be electrified in technically and economically efficient way. Node selection was carried out taking into consideration some important factors affecting the result such as demography, topography, socio-economic and techno feasibility factors of the area. The population and load density of a specific area was analyzed so that the load centers could be identified. Since the settlement in hilly region of Nepal is sparse, cluster of houses was selected. The coordinates were generated using Geo-referencing method of GIS and Google earth map.
The demographic data were taken with the help of governmental records, GIS, Topographical map and the satellite view of Google maps. After identifying settlements and their population density an outlook on the load was calculated by using a dummy load per household as described in unit 2(A). Based on the technical feasibility, 57 areas were delineated and respective numbers were given to each of those areas. The central coordinates (xi, yi) of each cluster within an area were determined, and then the coordinate of the resultant load center (X, Y) was solved as shown below:
Abbildung in dieser Leseprobe nicht enthalten
Where, i is the number of each cluster within an area for single load center, ni is the number of households present in specific cluster and (x, y) be the central coordinate of each cluster. The 10 meter is given for the consideration to address the problem of land use regulation, cost of land, land availability, software error etc. So the locations of nodes were selected by identifying suitable place within a radius of 10 meters. Monte-Carlo Simulation can be used to compensate for potential random errors.
The research area of this study is located in hilly region of the country, where the location of proposed nodes occurred from (28°43'49.14"N) to (29° 1'13.87"N) in south north direction, (81°22'37.57"E) to (81°36'9.96"E) in east west direction, with altitude variation from 494 m of sea level to 1976 m. The project area is unique in itself and have its own characteristics defined by steep hills, river crossings, forest and frequent altitude variation. All these factors contribute significantly to the design of the electrical network.
The possible path for the electrification was identified with the least distance between all the nodes, based on the online survey with the help of different maps. The criterion for selection of possible way was based on the technical, physical, environmental, economic and social consideration. After that, distance between the nodes with possible way was calculated. Then, selection of network was completed considering distance from the least to greatest according to the Kruskal’s algorithm.
In order to optimize the electrical network for rural electrification in Upper Karnali hydropower project affected area, the flow chart used is given in figure 8, and the algorithm is given as below;
Abbildung in dieser Leseprobe nicht enthalten
Figure 8: Flow Chart [25]
The complete grid network computed by using Kruskal’s algorithm is shown in Figure 9 below. The detail location and the number of households in each node is given in annex 2. Similarly, the data regarding the kruskal’s algorithm is presented in annex 3. The electrical network algorithm was applied by selecting the least distance paths between the nodes sequentially. There are 57 nodes in total, with 224 households per node in average. The total length of the grid was found to be 144.59 km. This network can be used for grid development to access electricity to whole affected area of the hydro project.
Abbildung in dieser Leseprobe nicht enthalten
Figure 9: Optimum Grid Network (i)
Further, to simplify the network and its analysis, the whole system is divided into 3 branches with their sub branches as shown in figure 10. A linear system is drawn between substation and distanced load center for each branch, so that analysis can be done easily. The distance of distinct load center and total distance for all of the branches are given in Table 2.
Abbildung in dieser Leseprobe nicht enthalten
Figure 10: Optimum Grid Network (ii)
In case of Nepal, the secondary distribution is found to have the voltage level of 230V in single phase system and 400 V in 3 phase system, and 3.3kV, 6.6kV, 11kV, 22kV or 33kV of primary distribution system. Variation in utilization voltage occurs due to the voltage drop in conductor and irregularity of the network design. As per rules and regulation, the voltage fluctuation shall not be allowed for more than 5% and frequency for more than 2.5%[8]. But in rural electrification, the voltage drop is found to be very high resulting variation of utilization voltage level by home to home[25]. Efficient and reliable technology must be applied in planning and design of the distribution system, so that efficient results are obtained.
The empirical formula for Economic Voltage Level is given by equation,
Abbildung in dieser Leseprobe nicht enthalten
Where V is the economic voltage level in kV, L is the total length of the line in km and P is the power to be transmitted in kVA. The probable voltage level of grid line depends upon the length of the line and power to be transmitted.
In the case study, there are 3 branches as shown in figure 10 (ii). Total length and the longer distance of each branch are given in Table 2 below. The peak demand for each branch is also given. The peak load for each of the branches is a multiplication of the households that would be supplied by respective branches, and peak demand assumed per household (i.e. 200 W). The most economic voltage level for all of the branches is calculated using equation (8), and tabulated in the same Table. Since, different values of economic voltage level are obtained, an optimized value (i.e. 33 kV) is considered by trial and error method. This is done to minimize the complexity of the analysis.
Table 2: Economic Voltage Selection
Abbildung in dieser Leseprobe nicht enthalten
To be beneficial from electrification, the transmission and distribution system of power system must be efficient and cost effective as the conductors used in transmission and distribution systems are one of the important and expensive components. In the transmission of electrical power, the resistance and reactance of the conductor play important roles. Resistance provides the power loss in the system and voltage regulation affects the quality of the service. So, the conductor should be selected with possible low resistance and voltage regulation.
[...]
