STUDY ON LIGHTNING PROTECTION FOR PV SYSTEM
MOHD HISANUDDIN BIN ZAMHARIR
A report submitted in partial fulfillment of the requirements for the Degree of Electrical Engineering (Industrial Power)
Faculty of Electrical Engineering
UNIVERSITI TEKNIKAL MALAYSIA MELAKA
I declare that this report entitle “Study on Lightning Protection for PV System” is the result of my own research except as cited in references. The report has not been accepted for any
degree and is not concurrently submitted in candidature of any other degree.
Signature : …………..……….
Name : MOHD HISANUDDIN BIN ZAMHARIR
“I hereby declare that I have read through this report entitle “Study on Lightning Protection for PV System” and found that it has comply the partial fulfillment for awarding the degree of
Bachelor of Electrical Engineering (Industrial Power)
Signature :…………..……….
Supervisor’s Name : MR. ZIKRI ABADI BIN BAHARUDIN
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ACKNOWLEDGEMENT
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ABSTRACT
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ABSTRAK
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TABLE OF CONTENTS
CHAPTER 1 2 TITLE ACKNOWLEDEMENT ABSTARCT ABSTRAK
TABLE OF CONTENTS LIST OF TABLES LIST OF FIGURES LIST OF SYMBOLS
INTRODUCTION
1.1 Introduction
1.2 Problem Statement
1.3 Objective
1.4 Scope
1.5 Thesis Outline
LITERATURE REVIEW
2.1 Introduction
2.2 Photovoltaic (PV)
2.2.1 Photovoltaic Cell 2.2.2 Photovoltaic Module 2.2.3 Photovoltaic Array
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3
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2.2.4.3 Inverter
2.2.5 Grid-connected Photovoltaic System
2.2.5.1 MPPT
2.3 Standard Lightning Impulse
2.4 Impulse Generator Circuit
2.5 Lightning
2.5.1 Type of Lightning Discharge
2.6 Lightning Protection for PV System
2.6.1 Lightning Protection System (LPS)
2.6.2 Surge Protective Device
METHODOLOGY
3.1 Introduction
3.2 Literature Review
3.3 Set up an Experiment
3.3.1 Circuit Elements of Impulse Voltage Generator
3.3.1.1 Diode
3.3.1.2 Smoothing and Energy Storage Capacitor
3.3.1.3 Parallel Resistor 3.3.1.4 Series Resistor 3.3.1.5 Measuring Resistor 3.3.2 Impulse Voltage Configuration
Circuit
3.4 Conduct an Experiment
RESULT
4.1 Project Background
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4.2 Solar Panel without SPD
4.3 Solar Panel with SPD
4.4 Solar Panel with Shield Cable but
without SPD
4.5 Solar Panel with Shield Cable and SPD
ANALYSIS & DISCUSSION
5.1 Capacitance Divider
5.2 Peak Induced Voltage
5.3 Duration of Induced Voltage
5.4 Discussion
CONCLUSION & RECOMMENDATION
REFERENCES
APPENDIX A APPENDIX B APPENDIX C APPENDIX D
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36 39
42 42 43 46 48
49
50
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LIST OF TABLES
TABLE 2.1
5.1 5.2
TITLE
Possible installation of surge protective device depending on LPS
Results of peak induced voltage from the experiment The duration of induced voltage in the photovoltaic system
PAGE
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LIST OF FIGURES
FIGURE 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 2.10 2.11 2.12 2.13 2.14 2.15 3.1 3.2 3.3 3.4 3.5 3.6 TITLE
Single diode model of PV cell
V-I Characteristic by assuming �� is negligible and ��ℎ
is infinite
V-I characteristic of PV module (Varying cell temperature) V-I characteristic of PV module (Varying sun intensity) Block diagram for stand alone solar system
Charger controller DC-AC converts process
Grid-connected Photovoltaic System
Impulse wave (double exponential waveform) Circuit for produce impulse wave
Lightning phenomena
Type of lightning discharge a) negative downward lightning, b) positive downward lightning, c) negative upward lightning, d) positive upward lightning
Effect of lightning strike on PV module Destroyed inverter
Cone protection zone provide by air terminal Flow chart of project methodology
Diode
Smoothing and Energy Storage Capacitor Measuring capacitor
Circuit to generate impulse voltage using impulse voltage generator
Impulse voltage generator configuration in lab
xi 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 4.10 4.11 4.12 5.1 5.2 5.3 5.4 5.5 5.6 5.7
Impulse voltage as input when the solar panel without SPD
The unwanted signal from solar panel without SPD Impulse voltage and unwanted signal from solar panel without SPD
Impulse voltage as input when the solar panel with SPD The unwanted signal from solar panel with SPD
Impulse voltage and unwanted signal from solar panel with SPD
Impulse voltage as input when the solar panel with shield but without SPD
The unwanted signal from solar panel shield cable but without SPD
Impulse voltage and unwanted signal from solar panel with shield cable but without SPD
Impulse voltage as input when the solar panel with shield cable and SPD
The unwanted signal from solar panel with shield cable and SPD
Impulse voltage and unwanted signal from solar panel with shield cable and SPD
Capacitance divider on measuring capacitor Peak induced voltage on solar panel without SPD
Peak induced voltage on solar panel with SPD Peak induced voltage on solar panel without SPD but
with shield cable
Peak induced voltage on solar panel with SPD and shield cable
Induced voltage gradually decrease
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LIST OF SYMBOLS
��ℎ - Shunt Resistor
�� - Series Resistor
���. - Current generated by the incident light
�� - Diode current
�� - Current through shunt resistor
�� - Leakage current of diode
� - Electron charge
� - Boltzmann constant
� - Ideality factor
�� - Band energy gap of the semiconductor
�� - Nominal temperature (298 Kelvin)
� - Voltage
� - Current
� - Temperature
��� - Short circuit current of the PV module
��� - Open circuit voltage of the PV module
�� - Thermal voltage
������ - Wave front time
�ℎ��� - Half amplitude time
CHAPTER 1
INTRODUCTION
1.1 Introduction
2
1.2 Problem Statement
Solar energy is a kind of renewable energy that is widely used nowadays. Solar energy is an alternative solution to overcome fossil fuel crisis. It is come from radiation of sun coming to earth in a day[1]. Photovoltaic (PV) is a term that refers to convert solar energy that come from sun to electrical energy by solar cell. The research of photovoltaic system is very useful and relevance nowadays. To generate electricity in large amount, solar cell that expose to radiation of sun must be in large size. However, large size of solar cell may have a tendency to increase the probability to be effected by lightning strike activity. Lightning strike is a natural phenomenon that caused by electric discharge in the atmosphere. Lightning produce very high voltage that can damage photovoltaic system by creating the streamer from sharp edges or the around the corner. Furthermore, the lightning strike can induce the unwanted signal that may propagating the radiation electric field through the solar panel and pass the unwanted current to the electrical system. For that reason, lightning protection on photovoltaic system is very important to avoid the effect of the strike damaging the photovoltaic system. This thesis is purposely to study the propagation effect of the induce voltage to the solar panel by the horizontal discharge which produced by 1.2/50µs lightning wave shape. This lightning wave shape is generated by the impulse generator in FKE’s HV lab. The results from experiments were used to observe and to investigate the characteristics of unwanted signal that couple to the solar panel system.
1.3 Objective
The objectives of this project are
1. To investigate the characteristics of unwanted signal that propagate and couple to the solar panel system by generating the lightning artificial discharge (1.2/50µs) in horizontal orientation layout.
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3. To investigate and provide the effective of shielding technique in reducing the effect of unwanted signal for photovoltaic system.
1.4 Scope
The scope of this project includes
1. Generating the lightning impulse voltage (1.2/50µs) with of 20 to 30kV which connected with measuring unit (DMI551)
2. The photovoltaic system comprising 12V solar panel, tube gas discharge as surge protective device (SPD) and coaxial cable 75Ω impedance connected to oscilloscope.
3. The spark gap was set in horizontal in such a way that it can produce the induce voltage discharge in horizontal orientation while the panel was located approximately 3 meter from the spark gap and set as vertical position.
1.5 Thesis Outline
CHAPTER 2
LITERATURE REVIEW
2.1 Introduction
Literature review is implemented to understand the concept of lightning protection on photovoltaic system. Literature review is executed by using several references such as IEEE journals, book and some internet resource. It is important to understand the concept of this project before proceed with conduct an experiment on lightning protection on photovoltaic system. Several concepts of cases which are related to the project will be explained in this chapter.
2.2 Photovoltaic (PV)
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2.2.1 Photovoltaic Cell
Photovoltaic cell is also known as solar cell. It is not work during darkness and usually is made from semiconductor material such as silicon. When the photovoltaic cell exposed to sun, the photons in form of light are converted into electrons. The photons that flow through the PN junction in solar cell randomly strike the atom and give energy to the outer electron that make the electron can break freely from the atom. The photons in the process are converted to electron movement are called electric energy [2]. Photovoltaic cell is a simplest component of a photovoltaic module that can generate very small current. A photovoltaic cell usually represented as an equivalent single diode model. Figure 2.1 show single diode model of photovoltaic cell.
Figure 2.1: Single diode model of PV cell [3]
A practical photovoltaic cell is deemed to be current source with a parallel forward diode [4]. This model contain a current source ��ℎ with a parallel forward diode, a parallel resistance ��ℎ and a series resistance ��. Series resistance, �� represent the resistance inside PV cell.
Forward current �� that flow through the diode is view as dark current or diode current.
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�= ��� − �� − �� (2.1)
�=��� − ���exp��(�+���
��� � −1� −
�+���
��ℎ (2.2)
Where,
��� : current generated by the incident light
�� : diode current
�� : current through shunt resistor
�� : leakage current of diode
� : electron charge (1.6 × 10−19�)
� : Boltzmann constant (1.38 × 10−23�/�)
� : ideality factor that varies between 1.0 to 1.5
Equation (2.1) and (2.2) can be representing by applied Kirchoff’s current law to the circuit. The V-I characteristic of PV module when assuming that �� is negligible and ��ℎ is infinite is shown in Figure 2.2.
Figure 2.2: V-I Characteristic by assuming �� is negligible and ��� is infinite[4]
Leakage current of diode or diode saturation current,�� can be expressed by Equation (2.3).
�� = ��,��
��
� �
3
��� ����� �� �1
� −
1
��� (2.3) Where,
�� : band energy gap of the semiconductor
�� : nominal temperature (298 Kelvin)
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��,� =
���
��� ����
���� −1
(2.4)
Where,
��� : short circuit current of the PV module
��� : open circuit voltage of the PV module
�� : thermal voltage that can be defined as, �� =����/�
2.2.2 Photovoltaic Module
A photovoltaic module is a package of connected photovoltaic cells. The current generated by the photovoltaic module and the V-I characteristic of the module are influenced by intensity of sun and temperature. The V-I characteristic of the module when varying the cell temperature is be shown in Figure 2.3. As the cell temperature of module increase, the open circuit voltage will decrease and the short circuit current almost constant. If sun intensity increase, the open circuit voltage will maintain almost constant while the short circuit current will increase obviously [3]. The V-I characteristic of the module when varying the sun intensity is be shown in Figure 2.4. Photovoltaic module has a point that can produce the greatest output power under a certain external environment. This point is call maximum power point.
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Figure 2.4: V-I characteristic of PV module (Varying sun intensity) [4]
2.2.3 Photovoltaic Array
Photovoltaic array is photovoltaic module that connected in series or parallel. It connected in series or parallel depends on output that is needed. Solar panel arrays feature a series of interconnected positive (+) and negative (–) outputs of solar panels in a series or parallel arrangement that provides a required dc voltage to inverter[5]. Photovoltaic modules that connected in series will cause the system to produce maximum output power with the same current. Maximum output power with same voltage will be produce from photovoltaic modules that connected in parallel.
2.2.4 Stand Alone Solar System
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Figure 2.5: Block diagram for stand alone solar system[6]
2.2.4.1 Charger Controller
Charger controller also known as regulator is design to protect the battery from overcharging. It also functions to control the energy flow to the system and by collecting information on the battery voltage and knowing the maximum and minimum values acceptable for the battery voltage. It can shut down the load when the battery reaches a prescribed state of discharge and can control the level of charging the battery before the battery is overcharging. Photovoltaic array is disconnected by charger controller when the battery reaches the maximum voltage and connected again when the voltage of battery decrease at a certain value. Figure 2.6 show the charger controller.
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2.2.4.2 Battery
Radiation from sun only can be used by solar panel to supply power during day. So, storage must be added to the system. Battery is a storage device that can be used to store energy from solar panel during daylight. During night, load that connected to the photovoltaic system will get supply voltage from the battery that has been charged. Size of battery that is use for photovoltaic system is depends on the demand voltage by the load that connected to the photovoltaic system. Battery usually size in ampere hour (Ah) unit. For photovoltaic system, the battery that is use is rechargeable battery. There are many type of rechargeable battery such as nickel-cadmium, nickel-metal hydride, lead-acid and nickel-zinc that can be used for photovoltaic system. However, the lead-acid battery is still most common use as storage in photovoltaic system.
2.2.4.3 Inverter
Solar panel only generates direct current (DC) that only can be used by limited number of load. When a photovoltaic system has an alternating current (AC) load, an inverter must be included in the system to convert DC output to AC output. Most of residential devices and appliances need AC as the supply. An inverter is a converter where the power flow is from the DC to the AC side, namely having a DC voltage, as input, it produces a desired AC voltage, as output. The process of convert DC to AC output is shown in Figure 2.7.
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The function of the inverter is to keep on the AC side the voltage constant at the rated voltage 240V (single phase). Inverter also functions to convert the input power Pininto the output power P
out with the best possible efficiency. The inverter’s efficiency is shown in Equation (2.5)
� =����
��� =
����������
������ (2.5)
Where,
���: current required by the inverter from the DC side
���: input voltage for the inverter delivered by the DC side
