Voltage Profile Improvement Analysis of Laukahi Feeder Using Capacitor Bank and Solar PV

TABLE OF CONTENTS

ACKNOWLEDGMENTS

ABSTRACT

TABLE OF CONTENTS

LIST OF FIGURES

LIST OF TABLES

LIST OF ABBREVIATIONS

CHAPTER 1 INTRODUCTION
1.1 Background
1.2 Statement of problem
1.3 Significance of the study
1.4 Objectives
1.5 Limitations of the study
1.6 Organization of dissertation work

CHAPTER 2 LITERATURE REVIW
2.1 Electrical distribution system
2.2 Load Flow
2.3 Distributed Generation (DG):
2.3.1 Solar PV as a DG source
2.3.2 Capacitor Bank as a reactive power source
2.4 Optimization Techniques
2.4.1 Ant Colony Optimization (ACO)

CHAPTER 3 METHODOLOGY
3.1 Data collection
3.2 Load flow analysis using Forward/ Backward sweep algorithm
3.2.1 Backward sweep algorithm
3.2.2 Forward sweep algorithm
3.3 Branch loss calculation
3.4 Estimation of DG sizes
3.5 Location of DG penetration
3.5.1 Generating size and number of ants
3.5.2 Flow chart of Load flow (Forward/ Backward sweep algorithm)
3.5.3 Flow chart of ACO
3.6 Financial analysis of the proposed system

CHAPTER 4 DESCRIPTION OF EXISTING SYSTEM
4.1 Introduction
4.1.1 Inaruwa DCS
4.1.2 Laukahi feeder

CHAPTER 5 RESULTS AND DISCUSSION
5.1 IEEE 10 bus system
5.1.1 Load flow of IEEE 10 bus system
5.1.2 Implementation of ACO techniques in IEEE 10 bus system
5.1.3 DG integration in IEEE 10 bus
5.2 IEEE 33 bus test system
5.2.1 Load flow of IEEE 33 bus system
5.2.2 ACO technique implementation on IEEE 33 bus system
5.2.3 DG integration on IEEE 33 bus
5.2.4 ACO and PSO comparison in IEEE 33 bus system
5.2.5 Summary of Results for IEEE test Radial Distribution System
5.3 Laukahi feeder
5.3.1 Load flow of Laukahi feeder using FBSA
5.3.2 Implementation of ACO in Laukahi feeder
5.3.3 DG integration in Laukahi feeder
5.4 Economic analysis of Laukahi feeder
5.4.1 Revenue generation from the proposed system

CHAPTER 6 CONCLUSIONS AND RECOMMENDATIONS
6.1 Conclusions
6.2 Recommendations
6.3 Future work

REFERENCES

APPENDIX I
(Line data and load data of IEEE test system)
Load Data IEEE 33 bus
Line Data (IEEE-33 Bus)

APPENDIX II
(Load flow results of IEEE test systems)
Bus voltage of IEEE 10 bus system IEEE 10 bus Branch Loss
Bus voltage of IEEE 33 bus system
Branch loss of IEEE 33 bus system
Pheromone table IEEE 33 bus

APPENDIX III
Line Data and Load Data of Laukahi feeder
Load flow result of Laukahi feeder
Bus voltage of Laukahi feeder
Branch current of Laukahi feeder
Branch loss of Laukahi feeder

APPENDIX IV
Financial analysis of the proposed system

APPENDIX V
Energy tariff rates (Effective from Shrawan 1, 2073)

ACKNOWLEDGMENTS

This dissertation work would not have been possible without the guidance and help of some people and organizations who contributed their valuable assistance in the preparation and completion of this study. I express my gratitude to all the contributors.

First and foremost, my utmost gratitude to my supervisor Dr. Shailendra Kr. Jha, Asst. Professor, Kathmandu University in the Department of Electrical and Electronics Engineering whose guidance has the key role to accomplish this work.

I truly want to thank Mr. Rewat Chaudhary, Manager at Duhabi grid, for his outstanding co-operation. I am indebted to Er. Protshahan Shrestha of Inaruwa Distribution Centre for providing the necessary data of the concerned feeders at Inaruwa substation. I cannot proceed without mentioning the valuable cooperation and support of Mr. Ajay Singh, Mr. Ashish Shrestha and all of my classmates.

Last but not least, I would like to thank my ever-loving family members for the support and patience they have had with me during the period of my masters’ degree study at Kathmandu University.

ABSTRACT

This thesis report attempts to identify the causes and probable solution of voltage profile issues in the Terai part of Nepal, specifically focused on Laukahi feeder. The radial Laukahi feeder is approximately 65km and distributed with 11kV system voltage where the inception point is Inaruwa sub-station and terminates with various parts of Sunsari district, Nepal. Currently, many villages farther than this substation are getting extremely poor voltages with frequent interruption of the power supply. Irrigation projects and grinding mills located at these places are unable to operate at its optimum capacity. In addition, small consumers are unable to run electrical appliances all the time in a day, not even an electric fan in hot season. To analyze this problem, the system has been developed and simulated using MATLAB, and possible solutions are recommended.

Solar PV and Capacitor banks used as an active and a reactive power generating sources have to be penetrated at suitable buses of the system in order to improve the voltage profile of the feeder and to reduce the branch loss as well. Suitable size and location of the DG sources has been identified by using Ant Colony Optimization techniques. After integrating the active sources and reactive sources, branch losses of the system have been significantly reduced and the voltage profile has been improved at permissible level. IEEE 33 bus and IEEE 10 bus system have been adopted to validate the test results.

LIST OF FIGURES

Figure 1.1: Basic layout of an Electrical Power System

Figure 1.2: Radial Distribution System

Figure 1.3: Ring Main System

Figure 1.4: Interconnected System

Figure 2.1: Layout of Electrical power system [8]

Figure 2.6: Distribution System Loss

Figure 2.3: Modeling of Radial Distribution System

Figure 2.4: Solar PV (Cell, Module & Array) [26]

Figure 2.5: Basic layout of Solar PV as a DG source

Figure 2.6: Comparison of the three different search algorithms

Figure 2.7: Food foraging behavior of ant

Figure 2.12: Developing pheromone path in the distribution system

Figure 3.1: Data Collection Flow Diagram

Figure 3.2: Modeling of a feeder

Figure 3.3: Flow chart of FBSA load flow

Figure 3.4: Flow chart of ACO

Figure 4.2: Layout of Inaruwa DCS

Figure 4.3: Single line diagram of Laukahi feeder

Figure 5.1: IEEE 10 bus radial distribution system

Figure 5.2: Load flow of IEEE 10 bus

Figure 5.3: Branch loss of IEEE 10 bus system

Figure 5.4: Pheromone deposited in the IEEE 10 bus

Figure 5.5: IEEE 10 bus branch loss (with DG)

Figure 5.6: Impacts on branch loss (IEEE 10 Bus)

Figure 5.7: IEEE 10 bus system voltage

Figure 5.8: IEEE 33 bus test system SLD

Figure 5.9: IEEE 33 bus test system voltage

Figure 5.10: IEEE 33 bus branch loss

Figure 5.11: Pheromone level in IEEE 33 bus system

Figure 5.12: IEEE 33 bus system voltage with DG

Figure 5.13: IEEE 33 bus system branch loss with DG

Figure 5.14: Impact of DG on IEEE 33 bus system

Figure 5.16: SLD of Laukahi feeder

Figure 5.17: Load flow of Laukahi feeder

Figure 5.18: Branch loss of Laukahi feeder

Figure 5.19: Pheromone deposited on the branch of Laukahi feeder

Figure 5.20: Voltage at different case in Laukahi feeder

Figure 5.21: Effect on branch loss after DG integration

Figure 5.22: Branch loss of the Laukahi feeder

LIST OF TABLES

Table 1: Effect of DG penetration in distribution line [31]

Table 2: Parameter value of ACO algorithm

Table 3: Sample data table (considered pf=0.8)

Table 4: BraBus matrix table

Table 5: Direction of branch current in BraBus matrix

Table 6: Cost estimation for solar PV and Capacitor bank

Table 7: BraBus matrix of IEEE 10 bus system

Table 8: Size and location of DG in IEEE 10 bus

Table 9: Size & location of DG penetration on IEEE 33 bus

Table 10: Comparison of ACO and PSO in IEEE 33 bus system

Table 11: Summary of IEEE test results

Table 12: Bus number and location of Laukahi feeder

Table 13: Size and location of DG in Laukahi feeder

Table 14: Summary of Laukahi feeder

Table 15: Installation cost of Solar PV

Table 16: Cost estimation of Capacitor Bank

Table 17: Land lease rate

Table 18: Annual revenue from the proposed system

Table 19: Cash flow diagram of the proposed system

Table 20: Summary of financial analysis for the proposed system

Table 21: Pheromone table of IEEE33 bus system

LIST OF ABBREVIATIONS

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LIST OF SYMBOLS

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CHAPTER 1 INTRODUCTION

1.1 Background

Primary concern of the power system is to transmit the generated power to the required load centers. Many theories and research have been completed and many are ongoing related to the electrical power system [1]–[3]. In this regard, one most common objective behind those researches is to transmit bulk amount of healthy power with minimum loss. Electrical power system consists of various segments from generating stations to the point of connections of different voltage level consumers - primary consumer and secondary consumer. Further, depending upon the voltage range, consumers have been given the name as the voltage they have consumed- low voltage (400/230V), medium voltage (11kV/33kV/66kV) and high voltage (132kV and above) consumers. These nomenclatures might be different with the country; however, the system is almost identical.

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Figure 1.1: Basic layout of an Electrical Power System

Generating stations generate the power, and the combination of transmission and distribution line transmits that power from generating stations to the end use consumers. During the flow of power, losses has been present in various segments of the power system, transmission and distribution line loss is the most significant one compared to other loss. World bank report shows that in 2015, total transmission and distribution loss was nearly about 32% to the total loss [4]. However, NEAclaimed that distribution system loss was limited to 16.83% of total loss in FY 2016/2017.

Power generation in Nepal is hydro dominant, as this is one of the abundant water resources country in the world. Almost all of the hydropower projects are located in hilly region due to its own nature. On the other hand, the load centers are situated in Terai region. To transmit this power from generating stations to the load centers significant amount of power loss has been encountered. Moreover, remote areas are sparsely populated; however, the state has a responsibility to provide electricity up to them whatever the load they consume. NEAannual report 2017 stated that most of the distribution losses was encounter in rural areas. In those areas, voltage profile issues are significantly raising with increasing the local market and incorporation of small industries as the country has proclaimed federal state.

As per scheme of connection, following distribution system arrangements are most in common:

a) Radial Distribution system
b) Ring-Main system
c) Inter-connected system

In radial distribution system, power has been fed through single source to the consumers. Though this system has been considered as poor reliability, arrangements are pretty simple and could have incorporated in much lower cost compared to other scheme.

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Figure 1.2: Radial Distribution System

This system has dominantly used in Nepal, for instance Laukahi feeder. Radial Distribution system (RDS) has certain limitations. It is preferred to run in shorter distances because of significant I[2]R loss. Further, consumers at far end suffer severe voltage issues if the line is heavily loaded.

On the other hand, Ring-main system is an improved version of radial distribution system. Though this system also contains single power feeding source, starting and ending point of the feeder is connected at a point as shown in Figure 1.3. Voltage fluctuations problem has been somehow improved in this system compared to the radial distribution system. In addition to this, if fault occurs at any side of the feeder, power supply can be maintained without interruption. Yet this scheme is costlier than previous system.

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Figure 1.3: Ring Main System

Interconnected system is a combination of radial system as well as ring-main system with multiple power feeding source as shown in Figure 1.4

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Figure 1.4: Interconnected System

Losses in the distribution system are generally categorized in two types: technical losses and non-technical losses. Technical loss is mainly due to the flow of electric current whereas the non-technical loss is associated with the human error (intentional or not). Due to current flowing in the electrical network, copper loss (I[2]R loss) occurs significantly compared to dielectric losses and induction & radiation losses [5]. Some of the listed cause of technical losses are:

a) Harmonic distortion
b) Arbitrarily expansion of distribution line
c) Unbalanced loading
d) Loss due to overloading and poor voltage
e) Losses due to lower standard of equipment

In this research work, cause (d) has been analyzed considering other causes in an acceptable range.

1.2 Statement of problem

There is still significant gap between energy supply and demand even though NEAhas announced ‘No Planned Load-shedding’ in the country, Nepal. Industrial sectors in Terai region are mostly suffering from energy scarcity; however, the situation is somehow better than before because of power stability. In FY 2016/2017, total 2287.5 GWhof energy was produced from the 17 existing NEAowned hydropower stations with the installed capacity of 469.29 MW. However daily peak electricity demand reached 1270MW (NEAannual report 2017). To fulfill this surplus demand, NEAhad been importing power from India using different cross boarder transmission lines. In Terai region, some area - Biratnagar, Rajbiraj, Lahan etc. for instance – are operating in isolated mode from the national grid and the power supply depends on the imported power from the India. In addition, these regions are facing voltage profile issues, which is troublesome to the consumer as well as the utility. Power being imported using 132kV transmission line is received at 121-128kV at the receiving end, and further it is being worse while sending it to the LV (11kV or lower)consumers.

1.3 Significance of the study

Line data and load data -Resistance (R), Reactance (X), Active Power (P) & Reactive Power (Q) – is required to perform the load flow study using forward-backward sweep algorithm in MATLAB. Using this load flow result, approximate line loss and voltage profile of the feeder can be estimated. Appropriate size and location of the DG and the capacitor bank can be identified by using ant colony search algorithm in order to improve the voltage profile and the line loss of the feeder. Further, line loss in terms of money and the cost of the system required to improve the voltage profile can be estimated using MS-Excel.

1.4 Objectives

The main objective of this research work is to improve the voltage profile of the Laukahi feeder within the permissible level, as well as to reduce the associated branch losses. The main objective will be achieved through following specific objective:

a) To identify the voltage profile and the branch loss of the line
b) To identify the suitable place to penetrate the solar PV and capacitor banks.
c) To compare the line loss before and after the DG and the capacitor banks penetration.
d) To check the financial viability of the proposed system.

1.5 Limitations of the study

a) Capacitor bank and solar PV are considered as reactive and active power sources respectively.
b) Study will be done only in Laukahi feeder because of data availability.
c) Any additional protection system required by the DG sourceshas been ignored.
d) Harmonics generated by non-linear devices is ignored.

1.6 Organization of dissertation work

This thesis work has been organized in six different chapters. In Chapter 1, general overview of power system and distribution network has been considered. In Chapter 2, the thesis work related literatures has been explained. In addition to this, research outcomes regarding DG system and optimization techniques have explained briefly. Methodology section has been described in Chapter 3. The process of identifying DG size and its location has mentioned, in addition to ACOimplementation techniques. In chapter 4, real case scenario has been explained. Based on the methodology applied on the IEEE test system and the real system, output results and its effects has been presented in Chapter 5. Moreover, financial consideration of the proposed system has been discussed in this chapter. Finally, in Chapter 6, conclusions of this thesis work have been presented and possible recommendations have been suggested.

CHAPTER 2 LITERATURE REVIW

2.1 Electrical distribution system

Nepal is a country dominated by a hydro power; yet power extractions from other renewable sources, wind and solar specifically, has been emerging nowadays. Even though our neighborhood countries are able to generate hundreds of Megawatts power from Solar, electricity from the hydropower is still the cheapest in long run for Nepal due to abundance of natural resources [6], [7]. To transmit the generated power electricity follows series of paths as depicted in the Figure 2.1. With the transmission of power, certain amounts of generated power are dissipating as a heat due to I[2]R loss in the transmission and distribution line.

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Figure 2.1: Layout of Electrical power system [8]

Electrical distribution system mainly consists of direct and indirect losses. Direct loss is associated with the magnitude of flowing current (I[2]R and I[2]X loss) where the indirect loss represents the loss due to human involvement, intentionally or unintentionally, as shown in Figure 2.2 [2] [6].

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Figure 2.2: Distribution System Loss

Electricity is a prime source of energy to run the modern appliances in order to make a human life easier. According to the requirement of various power outputs, utility has been provided different voltage levels as per the demand of consumers. Power generating stations, transmission lines and distribution lines are the major sectors of the power systems along with the substation. Substations transform voltage from high to low, or the reverse, or perform any of several other important functions. Between the generating stations and the consumers, electric power may flow through several substations at different voltage level.

The distribution power lines have some power quality problems such as voltage drop, voltage sag, voltage fluctuation, voltage flicker, transient voltages etc. These are some common problems in the distribution systems globally. These problems are occurred due to reasons such as loading pattern, length of the line, consumer behavior in the feeder etc. [9].

Considering configuration, electrical distribution system arrangements generally consists of three types of arrangements: a) Radial b) Loop and c) Network. Radial distribution system is popular in sparsely populated area among other structures due to low cost and simple construction [10]. However, poor voltage profile and less reliability are the major disadvantages of this system.

Electrical distribution system has some unique characteristics than transmission line. Some of the characteristics of distribution system are listed below:

a) Radial or weakly meshed structure
b) Multiphase and unbalanced operation
c) Unbalanced distributed load
d) Extremely large number of branches and nodes
e) High R/X ratio

Generally, the R/X ratio of the distribution system is very high resulting in the high voltage drop and power loss in the system. Due to these characteristics, conventional Newton Raphson and Gauss Seidel methods may provide inaccurate results and also may fail to converge [11].

Dirty power is known as the quality of power deviation from the agreed standard by the utility. If the demand increases beyond the limits then the system gets collapsed. Further, there must be a quantity of reactive power supplied in the line as per demand of the loads otherwise the system gets suffered from voltage stability issue. This issue is generally classified in two terms: total voltage collapse and partial voltage collapse. Whereas, excess reactive power results in voltage increase while a deficit of reactive power results in a voltage decrease [12]. Not only the voltage issues, some other effects are also associated with the term dirty power. It consists of power frequency variations and harmonics or waveform distortions also.

2.2 Load Flow

Basic objective of load flow is to ensure the quality of power being delivered from the generating source to the end use consumers. Generally, Load flow study is carried out if the new power system network is to be incorporated or if restructure of the network is required. It is the preliminary step to perform in power system planning, operation, expansion and reconfiguration [2], [13].

Some Load flow methods typically preferred in transmission line, Gauss-Seidel and NR method, are not applicable in distribution system due to its robustness and unique characteristics. For that reason, various load flow equations applicable for radial distribution system has been proposed in [11], [14]–[19]. Moreover, forward and backward sweep algorithm is quite popular among them due to its easiest modulation [20]. In this method simple Kirchhoff’s current and voltage law has been used to calculate branch current and bus voltage. In backward sweep, current will be calculated from the end node by Si/Vi and reached to starting node by summing up the branch current by KCLthen start to forward sweep. Initial bus voltage will be considered 1 pu, then other voltage will be carried out with the help of branch current and impedance [21]. For instance, V2 = V1 – Ib1 Z12 as shown in Figure 2.3.

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Figure 2.3: Modeling of Radial Distribution System

Calculated bus voltage and branch current are used to identify the branch losses and further planning of the electrical distribution network.

2.3 Distributed Generation (DG):

Electrical generation source has constraint output; however, the demand is varying with various parameters -time, income, weather, season etc. Major responsibility of the utility to provide the electricity as per demand is quite challenging. With the invention of low-cost electricity using renewable sources, limitations of power generation sources and its generation places have been changed. To fill the gap between demand and generation, alternative energy sources and alternative place (where needed) for generation is being quite popular [22]. There is no typical size and sources has named as DG. It has different identification with the need of researchers; nevertheless, one common thing among them is, power generation source having less than main (or grid) generation sources (power supply capability) and is mostly situated in the load center is known as DG. It cannot be alternative but are supportive for main generation.

Though the definition of a DG is different with the author, understanding about it is almost the same. Any power sources supplies active power to the line which is connected to the consumers is known as DG, and it doesn’t necessarily require to produce the reactive power [3], [23], [24]. It could be in different form. For instance: single DG and mixed DG. If the solar PV is alone being used as a DG source then it is called as a single DG source. Further, if both solar PV and wind turbine have been used as a DG source, then it is said to be a mixed DG. In practice, different kinds of power generation technologies – traditional, CHP, renewable energy sources etc. - has been used as a DG sources. Not only this, in some areas, fuel cells are also using as an active DG [22].

2.3.1 Solar PV as a DG source

A PV cell is capable to generate very small voltage (0.5V- 0.8V) in the presence of sunlight. However, with the proper arrangement of this cell- cell, module and array- manufacturer are able generate the required voltage.

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Figure 2.4: Solar PV (Cell, Module & Array) [26]

Though the solar PV is generally accepted as an active source it is providing reactive power too in the grid with the help of an inverter. A 100 kVAPV inverter connected to a 110 kWp solar PV is able to provide up to 60 kVAralmost for a year [27].

Voltage generation using solar PV collector is in DC; however, our grid system is AC. In this situation, Inverter functions as a bridge between solar PV and AC grid which converts DC power into AC as shown in Figure 2.5. PWMinverter is mostly being used in this case.

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Figure 2.5: Basic layout of Solar PV as a DG source

Control panel in solar PV system is used to protect the solar PV and finally generated power from the solar PV is transmitted to the utility grid through net metering device [28].

As the DG sources mostly used to improve the voltage profile of the system, sometimes it gives the adverse impact on lightly loaded conditions. With increasing DG penetration level, voltage on various bus of the system starts to rise and needs to be controlled using voltage controller [29]. Additionally, it is found that maximum size of DG penetration should not exceed 40-50% of total connected load, considering transient stability limit. Moreover, it has been reported that if the size of the DG unit has been installed without any size limit, network protector has been tripped with surplus DG power [23].

2.3.2 Capacitor Bank as a reactive power source

One of the causes of voltage drop in distribution line is the flow of reactive power in the line due to reactive load connected in the network. Synchronous condenser and capacitor bank are the most accepted source to supply reactive power. Other sources of reactive power has been described in [30]. Considering cost and operating challenges, capacitor bank is being very popular in distribution system in order to improve the performance of the line [31]. In addition, it has been found that segments of capacitor banks combined with the other active DG sources are cost effective to improve the voltage profile and power factor as well as to reduce the line loss [32].

According to Sareef Sayed and Kumar Injeti [31], multiple active DG sources with the placement of multiple capacitor segments provides minimal loss in IEEE 33 bus test system compare to alone DG sources as shown in Table 1.

Table 1: Effect of DG penetration in distribution line [31]

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Other researches also shows that if the main objective is to minimize the line loss and need to improve the voltage profile of the system, then the use of capacitor bank with the multiple DG sources is the best among others [33].

2.4 Optimization Techniques

Optimization is the term used to get maximum output with the help of minimum input. In other words, it is the act of obtaining the best results under the given circumstances. Moreover, the main aim of optimization is to minimize the effort required to get the maximized benefit [34].

In radial distribution system, the principal objective of the optimization technique is to identify the optimum location and size of DG for insertion. It is found that Distributed Generation (DG) is used to address the increasing load demand with comparatively low cost in secondary distribution system. Appropriate size and location of DG benefits to voltage profile of the system as well as plays a significant role to reduce the loss of the line [35].

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