ENGINEERING THESISS ENG460

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1 S Realization of a setup for educational experiments and safe investigations of PV Grid Connected system aspects Mohsan Khodadoost 2/12/2009 A report submitted to the School of Engineering and Energy, Murdoch University in partial fulfillment of the requirements for the degree of Bachelor of Engineering Author: Mohsan Khodadoost Supervisor: Martina Calais

2 Abstract This report investigates the design, construction and testing of a lockable box that is part of the grid-connected PV system. This system is intended to be installed by the School of Engineering and Energy at the Murdoch University South street campus and this system will be placed at the (Out Door Test Area) of the Research Institute for Sustainable Energy (RISE). The main purpose of this system is to create a good sample of the grid-connected system for the students of the Renewable Engineering degree. This system will allow the students to perform their experiment on the system in a safe environment. This system specifically has been designed and built to perform the islanding test. The report begins by providing an overview of the system s background and explains the specific tasks and objectives of the project. Then it provides descriptions, design of wirings and mechanicals of each individual component. Especially, it investigates the Hall Effect technology in detail. The rest of the report describes the design and procedures for making the DC and AC Hall Effect boards. In addition, it describes the procedures, and necessary equipment for performing the test on the DC and AC Hall Effect boards. Through investigation it was found that the prototype system which was built by Benjamin Hug, did not comply with the Australian Standard (AS), because it was built prior to Australian Standard (2005). Therefore the new system must be completely redesigned to comply with the Australian Standard. In addition, this report investigates the theory behind the Hall Effect technology and current and voltage transducers as well as design and test of DC and AC Hall Effect boards.

3 Acknowledgments This project was a great challenge for me and while I was doing this project, I faced many problems. Many people helped me to solve the problems that emerged during this project. Therefore, I would like to thank all those who helped me to fulfil my tasks and do this project as it was expected. First, I would like to thank my supervisor Dr. Martina Calais, for offering this project to me and supporting me in all stages of the project. Then Dr. Graeme Cole for giving me background information on the project. Also thanks to lab technicians Will Stirling and Wayne Clarke who helped me with the testing the Hall Effect board and providing me with the required equipment in order to do my project. Finally thanks to Hari Sharma and Nigel Wilmot from RISE who helped me with the Independent AC source solution and Wiring diagram.

4 TABLE OF CONTENTS 1)INTRODUCTION ) INTRODUCTION OF THE PROJECT ) BACKGROUND ) THE SPECIFICE TASKS FOR THIS PROJECT AND PROJECT OBJECTIVE ) OUTLINE OF THE PROJECT...5 2)PHOTOVOLTAIC SYSTEM TECHNOLOGY ) PV MODULES AND THE TECHNOLOGY OF PV MODULES ) INVERTER TECHNOLOGY ) GRID-CONNECTED SYSTEM CONCEPT ) Grid connected PV system components ) Grid connected PV system with single inverter ) Multi inverter grid connected PV system ) ISLANDING ISSUES )DESIGN REALISATION AND DESCRIPTION OF INDIVIDUAL COMPONENTS ) INTRODUCTION ) HALL EFFECT BOARD ) Introduction ) What is the Hall Effect? ) Hall Effect Theory ) HALL EFFECT BOARD COMPONENTS ) Current transducer operation ) LA 25-NP Current transducer ) Voltage transducer operation ) LV 20-P voltage transducer ) HOW TO BUILD THE HALL EFFECT BOARD ) INVERTER ) DC-AC Plug&Power (Pacifica Solar) inverter ) How Plug&Power inverter works ) DC-AC OK4E-100 inverter ) How OK4E-100 inverter works ) DC POWER SUPPLY ) Introduction ) DC power supply Mean Well 40W T-40C ) DC power supply Mean Well 60W S ) PROTECTION ) Introduction ) Miniature circuit breaker ) Residual current devices ) Contactor relay ) Islanding switch ) Test points ) INDEPENDENT GRID CONNECTION ) Introduction...39

5 3.8.2) AC source 6813B AGILENT ) Diesel generator ) Stand-alone PV system with battery back up ) Islanding test procedures realisation ) Islanding test procedures ) Results ) LOCKABLE BOX DESIGN ) Introduction ) Lockable box ) Display panel ) Wiring diagram of the lockable box, display panel and determining cable size.50 4) HALL EFFECT BOARD TEST RESULTS ) INTRODUCTION ) TEST THE CURRENT AND VOLTAGE TRANSDUCER FOR THE LINEARITY WITH DC VOLTAGE ) Method and materials ) Calculating the voltage transducer input resistor ) CURRENT TRANSDUCER LINEARITY TEST PROCEDURES ) VOLTAGE TRANSDUCER LINEARITY TEST PROCEDURES ) TEST PROCEDURES OF THE DC HALL EFFECT BOARD ) Introduction ) Method and materials ) RESULTS OF THE LINEARITY TEST ON TRANSDUCERS ) RESULTS OF THE DC HALL EFFECT BOARD TEST ) AC HALL EFFECT BOARD ) Introduction ) Method and materials ) RESULTS OF THE TEST ON THE AC HALL EFFECT BOARD ) Current transducer test ) Converting the output signals to input signals (Current Transducer) ) Voltage transducer test )CONCLOSIONS AND FUTURE WORK ) CONCLUSIONS ) FUTURE WORK )APPENDIX ) CURRENT TRANSDUCER DATA SHEET ) VOLTAGE ETRANSDUCER DATA SHEET ) 24 VDC POWER SUPPLY DATA SHEET ) +/-15VDC POWER SUPPLY DATA SHEET ) AGILENT 6813B AC SOURCE DATA SHEET ) CIRCUIT BREAKER AND RCD DATA SHEET ) FOLDER AND FILE AVAILABLE ON THE CD ) FOLDER AND FILE AVAILABLE ON THE CD...91

6 7)REFERENCES...94

7 Chapter 1 1.1) Introduction Grid-connected photovoltaic (PV) systems have recently become more and most popular systems among the PV systems types in Australia. Figure 1.1 shows the increasing using of grid-connected systems within Australia. Figure1.1: the Australian PV market [1] The Greenhouse Effect, government support and subsidy programs, and the rising costs of electricity are some reasons why people are turning to renewable energy at the present. Due to increasing demand for PV systems and engineers familiar with such systems, the School of Engineering and Energy at Murdoch University intends to install a PV grid-connected system in the ROTA (RISE Outdoor Test Area) of the Research Institute for Sustainable Energy(RISE) for educational purposes, especially for Renewable Energy Engineering education. This system will increase student understanding about grid-connected PV systems and associated islanding phenomenon. It is proposed that this system has a lockable box with all the test points and measurement devices installed on the front cover. One of the reasons to use this lockable box is safety for students and other people using the system. Therefore, all equipment, which is accounted as hazardous, will be locked in the box, with only the test points, switches, analogue ammeters and voltmeters used by students being installed on the front cover. 1.2) Back ground A prototype of this system was built and tested at the Rockingham campus by Benjamin Hug in At the time Benjamin built the prototype system, Murdoch University proposed a new degree, the Renewable Energy Engineering Degree. The School of Engineering realized that to enhance the quality of this degree it would be desirable to 1 P a g e

8 have a grid-connected system as part of the lab exercises for students. Figure 1.2 shows the prototype system, which was built by Benjamin Hug (2002). Figure1.2: Display panel of the PV grid connected system [2] Benjamin Hug s work was performed prior to the publication of the Australian/New Zealand Standard Installation of photovoltaic (PV) arrays in It was therefore necessary to review and revisit the design with regards to the compliance to this standard. This was partially attempted by other engineering students in later years but not completed. They approached this project using information from Benjamin Hug s work. They worked on the PV module installation and worked on the proposed idea of a Lockable Box. I approached this project with respect to the information from previous students. So my starting point of this project was to read and understand more about the system and check available documentation on the previous system and then start my work towards developing and improving the existing documentations such as wiring diagrams, mechanical design and, if necessary, change or add to the existing documents and drawings. An important point is that this system is going to be used by students, so it requires a high level of safety. Primarily Benjamin Hug s prototype system required a protective cover. As can be seen from the figure 1.2, DC power supplies, AC meters as well as various circuit boards all are installed on a panel and without any protection or cover that can prevent contact with these parts. Therefore, in the new system all of these parts will be locked in the box that increases the safety of the system. As second issue with this system is the fact that one of the inverters purchased for the system is not accredited according to the Australian Standard This requires a careful review of the grid-connection of the system and possible replacement of the 2 P a g e

9 utility grid with an independent AC source, which can provide the PV inverters with the necessary grid voltage and frequency. 1.3) The specific tasks for this project and project objectives The specific tasks for this project are individually explained, in order to give a good overview of this project. Figure 1.3 shows the core elements of the PV grid-connected system to be included in the lockable box. The educational PV grid-connected system consists of two module oriented PV inverters (OKE4 and Plug & Power) that will be housed inside the box. Circuit breakers (CB s) provide disconnection means for the PV modules. In addition, the system has an option of connecting a local load (General Purpose Outlet, connected via an RCD), as can be seen in figure 1.3. This connection is between the output of the inverter prior to the connection of the independent AC source. Figure 1.3: basic grid-connected system Figure 1.4, shows the system with the analogue multimeters and Ammeters. They measure voltage and current on both DC and AC sides. Therefore, students are able to observe the current and voltage in different locations of the system; also, they can observe the voltage and current of the system under different conditions. 3 P a g e

10 Figure 1.4: grid-connected system with analogue ammeters and voltmeters Figure 1.5, shows the system with Hall Effect boards (Hall Effect is a technology that convert the high input voltage to low output voltage) and test points. The Hall Effect boards require a dual ±15 VDC power supply in order to operate, as can be seen in figure 1.5. The purposes of the Hall Effect board are, firstly to provide safety, because this device is able to convert the high input voltage to a low output voltage, and therefore the system is safe for use by students. Secondly, the Hall Effect boards allow students to observe the waveforms on the DC and AC sides on the oscilloscope. Figure 1.5: gird-connected system with Hall Effect boards and 15 VDC power supply 4 P a g e

11 Figure 1.6, shows the system with islanding test relay, switch and test points. The islanding test relay for operation requires a 24 VDC power supply, as can be seen from the figure 1.6. The islanding test is one of the most important lab exercises that students can perform on this system. In addition, students can experience the islanding issue on two different inverters, one of that is accredited (Plug&Power) and the other that is not accredited (OK4E-100). Figure 1.6: grid-connected system with the islanding test Summary, students will be able to conduct the following tests from the lockable box on the grid-connected system: Observe the characteristics of the grid connected system and inverter. Measure the DC voltages and currents and observe the voltage waveforms from two inverters. Measure the AC voltages and currents, and also observe the voltage waveforms from two different inverters. Conduct the islanding test on two different inverters. 1.4) Outline of the Thesis The objective of this work is to provide a design and realisation incorporating the elements listed above as well as providing some guidance on the realisation of the independent AC source. The remainder of this report is organised as follows. 5 P a g e

12 Chapter 2 Photovoltaic system technology This chapter provides some background information on PV technology, inverter technology, grid connected PV system concepts and the issues associated with islanding. Chapter 3 Design realisation and description of individual components This chapter describes individual comments of the educational system. Corresponding electrical and mechanical drawings are presented. Chapter 4 Hall Effect board test results This chapter reports on individual current and voltage transducer tests as well as DC and AC Hall Effect board tests. Procedures, results and their analyses are presented. Chapter 5 Conclusions and future work The final chapter contains a summary of the project and reviews tasks and objectives. In addition, this chapter defines future work on the project. 6 P a g e

13 Chapter 2 Photovoltaic System Technology The focus of this project is on grid-connected PV systems and islanding tests. Therefore, it is good to know the concepts behind the following components that form the system: PV module and technology Inverter technology Grid-connected PV system concepts Islanding issues 2.1) PV Modules and the technology of PV Modules This project will focus on the set-up of the lockable box, where components such as inverters and other components of the grid-connected system are installed. This section briefly describe the two different types of PV cells that can be used for the system and their current and voltage characteristics under different conditions such as light intensity and temperature. Solar cells are devices that are able to convert direct sunlight into electricity. Solar cells are usually made from silicon and they are similar to other electronic devices, like diodes. In the field, solar cells are usually assembled into a module. There are many different solar cells available on the market, and still more are under research and development. The most common semiconductor material used for the production of solar cells is silicon. Amongst the silicon solar cells three cell technologies are most common, these are monocrystalline, polycrystalline and amorphous. The most common silicon solar cells are polycrystalline because their production procedure is cheaper than monocrystalline solar cells and their efficiency is higher than those of amorphous silicon cells. Figure 2.1 shows the three types of silicon solar cells and figure 2.2 shows the basic structure of a crystalline silicon solar cell. A B C Figure 2.1: (A) single crystalline, (B) multicrystalline and (C) amorphous silicon 7 P a g e

14 Figure 2.2: Structure of the solar cell The irradiance and temperature are factors that can have direct effects on the amount of power output of the solar cell. For example, monocrystalline solar cells are capable of converting only 25% of the solar energy into electricity. This is due to the lack of energy in the sunlight spectrum; those photons that have energy more than bandgap-energy are able to convert their energy into electricity, which separates the positive and negative charges in the material. A typical monocrystalline silicon solar cell of 100cm 2 will produce around 1.5 W of power at 0.5V DC and 3 A under standard sunlight (1000 W/m 2 )and temperature (25⁰C). The power output of the solar cell is directly proportional to the intensity of the sunlight. It can be seen in figure 2.3 that sunlight intensity has a significant effect on the short circuit current. I SC Figure 2.3: I-V curves of monocrystalline solar cells at 25 degree and different irradiance [3] V OC 8 P a g e

15 Figure 2.4 shows the power curve of the monocrystalline silicon solar cell. The yellow curve relates to intensive sunlight, which gives the highest output power from the solar cell, while blue being low sunlight, gives the lowest power outpout. Power V OC Figure 2.4: Power curves of the monocrystalline solar cell with temperature of 25 degree and different irradiance[3] Figure 2.5 shows the effect of the ambient temperature on the solar cell. As it can be seen the ambient temberature has an effect on the open circuit voltage. Lower ambient temperature has higher open circuit voltage while higher ambient temperature will cause a lower open circuit voltage. 9 P a g e

16 I SC Figure 2.5: I-V curves of monocrystalline solar cell under standard irradiance (1000 W/m^2) and different ambient temperatures [3] V OC Figure 2.6 shows the effect the ambient temperature has on the power output of the monocrystalline solar cell. As it can be seen from the graph, high ambient temperature has low power output while low ambient temperature has higher power output. Power V OC Figure 2.6:Power curves of a monocrystalline solar cell under standard irradiance (1000W/m^2) and different ambient temperatures. [3] 10 P a g e

17 Polycrystalline solar cells have a lower efficiency than monocrystalline solar cells. The efficiency of commercial polycrystalline cells is about 13-16% and for commercial monocrystalline solar cells, the efficiency is about 15-18% at present. [4] The polycrystalline and monocrystalline modules are recommended for this system with the maximum voltage of 50 VDC and current of 4ADC. In addition, PV modules must comply with the IEC (International Electrotechnical Commission) 61215, which applies to crystalline silicon PV modules and contains standards for design and type. 2.2) Inverter technology An inverter is a device that is capable of converting DC voltages generated by PV modules into AC voltages, which can then be used by appliances in the home. In the area such as power generation where we are using grid-connected PV systems, we need inverters to Change the wave shape of current into a sinusoidal waveform Convert the DC current into AC current, and Boost the voltage of the PV array if it is lower than the grid voltage. A PV system that is connection to the grid requires a grid-connected inverter. Figure 2.7 shows a simple block diagram and topology of a grid-connected inverter. Figure 2.7: PV inverter with several conversion stages and high frequency transformer 11 P a g e

18 There are a number of different PV system configurations concepts that inverters can be connected to the PV modules. Each configuration has advantages and disadvantages, so which concept is chosen will depend on the type of application. Three common PV system configuration concepts are as follows: Module inverters In this method, each module has it own inverter. The inverters in this system are connected to the PV modules according to the module inverter concept (Figure 2.8). In this concept, each module is connected to an inverter. The advantages of this method are that the extension of the PV array is easy, that each module has its own MPP tracking, and that no DC Wiring is required because the inverter is next to the PV module. The lower lifetime, high cost and complicated replacement are disadvantages of this method. Figure 2.8: module inverter concept The module inverter is a good choice for a system when some of the modules are shaded in the system. In this case, there is no effect on the output power of the other modules within the system. Central inverter Central inverter is another way of the connecting the inverter in the system. The larger systems and stand-alone systems are usually connected in this way. Central inverter method has three configurations: 1. Extra low voltage concept: The advantages of a short string is that the shading effect has less effect on the string current, while the disadvantage of this concept is the resulting high currents which require a cable with larger cross-section area to reduce the losses. 12 P a g e

19 2. High voltage concept: The advantage of the high voltage concept is that cables with smaller crosssection area are required, with the disadvantage being that the system faces greater shading losses due to the longer string (When a set of PV modules are connected together in series is called string). 3. Master slave concept: This method is usually used for larger PV systems. The size of the total power out is divided by the number of inverters. One inverter acts as a master and others are slaves. In the condition that irradiance is low, only the master inverter works. By increasing the irradiance, the power will increase and the master inverter, which has a power limitation, will connect to the next inverter (slave) once the power limit is reached String inverters In the string inverter concept, one inverter is used per string. This method is suitable for a system where modules are differently oriented or there is shading. It is necessary to connect the modules with the same ambient conditions in one string. [4] As mentioned before, the inverter for the system must be a grid-connected inverter and it should comply with the Australian Standard section 4. This section has described the requirement of the grid-connected inverter. (For more information, refer to the Australian Standard ) 2.3) Grid-connected system concept Grid-connected PV systems are a relatively new application where a PV system is installed to supply power to a house, building or other load that is also connected to the utility grid. PV systems are increasingly integrated into buildings and are likely to become very common in the future. They are used to supply electricity to dwellings, commercial and industrial buildings. They are typically between 0.4kW and 100kW in size. The systems usually feed electricity back into the utility grid when electricity generated exceeds the load. These systems offer a number of advantages: Distribution losses are reduced because the systems are installed at the point of use, No extra space is required for the PV systems, Costs for mounting systems can be reduced if the PV module is integrated into the building, and The PV array itself can be used as roofing material or installed on the roof surface. The grid-connected system, compared to off-grid systems, is cheaper and requires less maintenance. The only maintenance required is to occasionally clean the PV modules to prevent any shading. Grid-connected systems usually do not require energy storage, which is a factor that can improve system efficiency and decrease the environment impact (as batteries are eliminated). In a grid connected PV system, batteries are an 13 P a g e

20 option but in the case where the system generates power continuously from a PV system, it is essential. Usually the grid will supply the load in situations when the PV generated electricity does not meet the load requirement. Due to grid access, standard AC power is available all the time. The only disadvantage of the grid connected PV systems is their inability to provide electricity if the utility is cut off due to islanding issues. Figure 2.9 shows a very basic block diagram of a grid-connected system. Figure 2.9: basic diagram of PV grid connected system 2.3.1) Grid-connected PV system components: PV modules: They are connected in parallel or a series to generate electricity. PV modules generate DC voltages. Inverter: An inverter is a device that is able to convert DC voltages to AC voltages. The output of inverters should match the voltage, frequency and power quality of the network. Load: Load refers to appliances that have been connected to the network of the building and are fed by the inverter. Meters: Meters show the amount of the energy drawn from the grid or fed by the PV system into the grid. Grid: A single or three-phase network that is managed by the electricity supplier. It can work as both a sink for excess generated electricity or as backup source for the system ) Grid connected PV system with a single inverter There are two concepts of the grid-connected PV system. They are as follows: The First type of grid-connected system is very common and it is cheaper. Most residential properties use this type of system. Figure 2.10 shows a single grid connected PV system. This type of system is very common for residential properties because the cost is reduced due to systems not having batteries. The size of this type of system being installed in residential properties is typically between 1 KW and 2KW. 14 P a g e

21 Inverter PV Module + Meter Meter Grid PV Module Figure 2.10: Single inverter grid-connected PV system 2.3.3) Multi inverter grid connected PV system This type of system is effective where there is a shading problem. If one or more of the PV modules are shaded, it would not have any effect on the output of the system because that particular module has its own inverter. Multi inverter grid-connected systems are more expensive than single inverters and are usually used for large-scale systems. Figure 2.11 shows a multi inverter grid-connected system. Figure 2.11: Multi inverter grid-connected PV system The system proposed in this project used this concept of the grid-connected PV system to be connected to the grid or independent AC source. The only difference between the proposed system and figure 2.11 is that the proposed system has no meters. The connection of the system to the grid must comply with the Australian Standards 5033 and ) Islanding issues When the system has been connected to the grid there is a phenomenon which may happen that is called islanding. This phenomenon may happen if the inverter does not disconnect itself from the grid after the grid fails. So if the inverter doesn t disconnect from the grid, it will supply the power to the grid which may cause some dangerous situations. Utility services do not like islanding because it is very dangerous for workers if they are working on the network. Therefore, the grid-connected system requires a grid-connected 15 P a g e

22 inverter. These types of inverters have special electronic system inside to prevent islanding. In fact, the lockable box, which is a part of the PV grid-connected system at the Murdoch University, is capable of doing islanding tests on two different inverters (Plug&Power and OK4). This box allows the students to experiment and experience the islanding phenomenon. According to the Australian Standard , the inverter shall stop operating within 2 seconds if grid voltage or frequency changes. (For more details, see the Australian Standard ) 16 P a g e

23 Chapter 3 Design realisation and description of individual components 3.1) Introduction In this chapter, all the components that should be installed in the lockable box will be introduced and described. In addition, the mechanical and electrical wiring of each component will be discussed. 3.2) Hall Effect Board 3.2.1) Introduction One of the main purposes of the system is to measure and observe voltages and currents on the DC and AC sides. The voltages and currents on the DC side are safe and there is no danger, but it is very dangerous to measure voltages and currents on the AC side. So I came up with the idea that the system should have an electronic device which is able to convert the voltage and current to a lower level. Hall Effect Technology was one of the best and apparently cheapest solutions for our problem. A few years ago, this system was built by Benjamin Hug as a practical project. When Benjamin built the system he used a shunt board to measure and observe the voltage and current of the DC side but due to safety in this project, it was proposed to change the shunt board to another Hall Effect board, which makes the system much safer for student use. This system is equipped with two Hall Effect boards; one of the Hall Effect boards is responsible for converting the DC current and voltage from the PV module to lower voltage. The other Hall Effect board is responsible for converting AC current and voltage out of the inverter to lower and safe voltages. In other words, the duty of the Hall Effect boards in this system is to provide a safe signal for students so that they are able to measure the current and voltage from the PV module (DC) and out of the inverter (AC). Each Hall Effect board consists of two current transducers, two voltage transducers and a set of resistors. Each board has two current transducers and two voltage transducers in order to measure and see the waveforms of DC and AC sides of the two inverters. This section will describe the Hall Effect Sensors and the theory behind them, and then describe the voltage and current transducers individually. Finally, description will be given the Hall Effect board wiring diagrams and the installation procedures ) What is the Hall Effect? The Hall Effect was first observed by Edwin Hall in While he was conducting experiments on gold foils he realized that when the current flows from one side to the other of a thin conductor (gold foils), and in the presence of a magnetic field, which is perpendicular to the strip, the electrons are deflected to one side of the gold foil. This phenomenon caused an excess electrical charge build-up, which gave rise to a voltage difference across the two sides of the foil. This voltage difference, which is perpendicular to both the magnetic field and current flow, is called the Hall Voltage. [5] 17 P a g e

24 Note: In the absence of a magnetic field or if the magnetic field is parallel to the strip, then there is no voltage difference between the two sides of the strip. Hall Effect is a technology that helps to convert high-level signals to low-level signals. This will allow us to do our measurement on high-level signals in a safe environment. One of the main reasons for using the Hall Effect board in the lockable box is to create a safe environment for students to measure and see the waveform of the voltages and currents in the AC and DC sides of inverters ) Hall Effect Theory The Hall Effect is based on electromagnetic theory. It can be observed by passing the current I through a flat conductor in the x direction and then applying a uniform magnetic field in the y direction as it shows in figure 3.1. If the charge carriers are electrons (negative) moving in the negative x direction with a drift velocity V d, they experience an upward magnetic force F B =qv d * B and are deflected upward, accumulating at the upper edge of the flat conductor, leaving an excess of positive charge at the lower edge (Figure 3.2). This accumulation of charge at the edge increases until the electric force resulting from the charge separation balances the magnetic force acting on the carriers. When the balance condition is reached, the electrons are no longer deflected upward. In this condition, it is possible to connect a voltmeter across the conductor and measure the Hall voltage that is generated across the conductor (Figure 3.2). If the charge carriers are positive, they will move in the positive x direction. As it is shown in the figure 3.3, they experience an upward magnetic force qv d * B. This is due to positive charge build-up on the upper edge and leaves an excess of negative charge on the lower edge. As a result of that the Hall voltage generated has an opposite sign. [6] Figure 3.1: The Hall Effect theory. Flat conductor, perpendicular magnetic field, presence of current and display for positive and negative carriers. 18 P a g e

25 Figure 3.2: Hall Effect technology when the carrier is negative 19 P a g e Figure 3.3: Hall Effect technology when the carrier is positive 3.3) Hall Effect Board components The Hall Effect board that has been used for the system consists of two current transducers, two voltage transducers and resistors ) Current Transducer Operation The closed loop current transducer consists of a Hall Effect generator, which is mounted, in an air gap magnetic core. A coil is wound around the core and a current amplifier is connected to the Hall sensor. A conductor carrying a current passes through the core and produces a magnetic field that has an effect on the Hall sensor. The Hall sensor is connected to a current amplifier. The current in the coil produces an opposite field to the current that passes through the conductor. The coil is connected to the output of the sensor. The output current is proportional to the current that passes through the core multiplied by the number of the turns on the coil. For example, a sensor with a 1000 turns coil produces an output of 1mA per ampere. The current transducer requires a DC power to operate. [7] Figure 3.4 shows the closed loop current transducer.

26 Figure 3.4: Current transducer interior components [7] 3.3.2) LA25-NP current transducer LA 25-NP is used for the measurement of DC, AC, pulsed and mixed currents. The primary has been isolated from secondary with a galvanic isolation and it has a case of plastic isolation. This current transducer is a closed loop multi range, which uses the Hall Effect technology. Figure 3.5 shows the LA 25-NP current transducer and connection terminals. [8] Advantages of this transducer are as follows: Excellent accuracy Very good linearity Low temperature drift Optimized response time Wide frequency bandwidth No insertion losses Current overload capability Figure 3.5: wiring diagram and terminals of the current transducer LA25-NP/SP13 20 P a g e

27 3.3.3) Voltage transducer Operation A resistor has been connected in series with the positive terminal of the voltage transducer to limit the large current that enters the voltage transducer. This limitation for input current into voltage transducer is due to limited input current of the voltage transducer. After the current enters the primary side, a magnetic flux will be created. The DC power supply, which is connected to the secondary side, will drive the current in the secondary winding and as a result of that, a magnetic flux will be produced. Then the hall device and the associated electronic circuit are used to generate the secondary current that is an exact representation of the primary voltage. Figure 3.6 shows the interior components of a voltage transducer. [9] +VDC Hall sensor Amplifier -HT Primary coil +HT R1 Rm Secondary Magnetic Current core with coil output Figure 3.6: Interior components of the voltage transducer -VDC 3.3.4) LV20-P voltage transducer The LV20-P voltage transducer is used to measure the AC, DC and pulsed voltage. The primary circuit has been isolated from the secondary by galvanic isolation. All components have been placed in the plastic case insulation. The voltage transducer is a closed loop that uses the Hall Effect technology. Figure 3.7 shows the LV20-P voltage transducer and connection terminals. [10] Figure 3.7: voltage transducer LV 20-P and connection terminals 21 P a g e

28 3.4) How to build the Hall Effect Board The Hall Effect transducers are installed on the electronic circuit board according to the design wiring diagram that is shown in figure 3.8. The following procedures describe how to build a DC Hall Effect board. Calculate the value for the input resistor to the voltage transducers (Refer to the transducers test for calculating the value of the input resistor) and calculate the appropriate cable sizes. (Refer to Australian Standard 3000 wiring rules and 3008 cable size)[11],[12] Produce the wiring diagram. (figure3.8) Select a proper circuit board and draw the wiring diagram on it. (The exact location of each component must be shown on the board.) Using a suitable soldering device, solder the components on the board. The installation process for both DC and AC Hall Effect boards are very similar. The only difference is in the input resistor of the voltage transducers which the resistors for AC Hall Effect Board are 22KΩ and 5W (22KΩ is selected because there is no 24KΩ resistor available on the market. The 24KΩ resistor will limit the current into voltage transducer for more information see the voltage transducer operation section 3.3.3) and DC Hall Effect are two resistors in series one 3.3KΩ and other one 1.2KΩ, 4.5KΩ in total. Figure 3.9 A shows the front of the DC Hall Effect board and figure 3.9 B shows back of the DC Hall Effect board. Figure 3.10 shows the wiring diagram of the AC Hall Effect board while figures 3.11 A and B show the completed AC Hall Effect board back and front. 22 P a g e

29 Figure 3.8: DC Hall Effect Board wiring diagram 23 P a g e

30 Current transducers Voltage transducers R 1 (input resistor) R m (output resistor) A B Figure 3.9: DC Hall Effect Board (A) front side (B) back side 24 P a g e

31 Figure 3.10: AC Hall Effect board wiring diagram 25 P a g e

32 R m (output resistor) Voltage transducers Current transducers R 1 (input resistor) A B Figure 3.11: AC Hall Effect Board (A) front side (B) back side 26 P a g e

33 3.5) Inverter In chapter 2, the inverter concepts and topology of the grid-connected inverter were described. This section will describe the Plug& Power and OK4E-100 inverters. These inverters are used for the proposed system ) DC-AC Plug&Power (Pacific Solar) inverter The Plug&Power, which is known as IPC-1 series (figure 3.12) has high efficiency and is suitable for grid-connected systems. It is possible to connect several Plug&Power inverter together very easily. The inverter can be connected to the PV module with an open circuit voltage of 50V or less, but the current must not exceed 4 A. The maximum output power of the inverter depends on the power from the solar cell. The IPC inverter monitors the grid and it will operate when the grid is present. If the grid is not present then the IPC inverter will go into standby mode. Figure 3.12: Plug&Power grid inverter (IPC) Plug&Power grid inverter specifications [1] Efficiency 91.8% Maximum Power Tracking Efficiency 99.9% PV Voltage Vdc PV Current 4 A (max) Rated Grid Voltage Vac Output Current 0.5 A(max) Ambient Temperature -20 ⁰C- +70⁰C PV Power 140 W (max) 3.5.2) How the Plug&Power (IPC) inverter works The Plug&Power inverter requires a set of conditions so that it starts working after a 1- minute delay. The delay ensures compatibility with the grid. The conditions are as follows: DC voltage greater than or equal to 24 V DC. The grid voltage rms must be 200 V rms 270. The grid frequency must be 49 Freq. AC 51 Hz. 27 P a g e

34 This inverter is designed to react when the grid is down by automatically disconnecting the system from the grid. Then it will restart after a 1-minute delay. [2] 3.5.3) DC-AC OK4E-100 inverter The OK4E-100 is a small-size high performance DC-AC grid-connected inverter (figure 3.13). This inverter has been designed for use in combination with a PV module that consists of 72 solar cells in series, and with a maximum output power of Watt. This inverter optimizes power transfer from the PV module to the grid by means of a maximum power point tracking algorithm (MPPT). It also monitors the grid voltage, phase and frequency before transferring the PV energy into the grid. OK4E-100 has not been designed to be used as a stand-alone system. This inverter has a maximum DC voltage of 50V. The OK4-100 is a perfect inverter for small systems. The size of OK4E- 100 is only 93x120x30mm, which is very compact in size. This is an advantage of this inverter. Figure 3.13: OK4E-100 grid inverter 28 P a g e

35 OK4E-100 grid inverter specifications [1] Efficiency 92% max MPPT efficiency 99% over 10% Ambient temperature -20 to +80 ⁰C Nominal power 130W Nominal voltage 24 Vdc PV module 72 cells in series Maximum voltage 50 Vdc MPPT voltage 24 to 50 V dc Starting power 24 V Nominal grid voltage 230 V Grid voltage range V Nominal grid frequency 50 Hz Grid frequency range Hz Power factor >0.99 Maximum Current 0.375A 3.5.4) How OK4E-100 inverter works The OK4E-100 operates just by connecting to the PV module. A DC voltage of 24 V or more can bring the inverter into standby mode. In the start-up sequence, the inverter first measures the grid voltage and frequency; then if they are within normal range, the inverter starts to transfer power from the PV modules to the grid. The grid is monitored continuously; any abnormality in the grid voltage or frequency will cause the inverter to disconnect itself from the grid. [2] 29 P a g e

36 3.6) DC Power Supply 3.6.1) Introduction Each Hall Effect board consists of two current transducers and two voltage transducers. These transducers use the Hall Effect technology. This technology requires an input signal and a power supply that supplies ±15 V DC so that an output signal can be obtained on the measured terminal. Therefore, the system requires a ±15 V DC switching-mode power supply to supply the voltage for the transducers. Besides transducers, the system is equipped with a contactor relay, which operates on 24 V DC. Therefore, the system requires a 24 V DC switching-mode power supply to supply power for the contact relay ) DC power supply Mean Well 40W T-40C Mean Well T-40C switching DC power supply is used to supplying ±15 VDC to both Hall Effect Boards. This power source has been selected because it has small size, which makes it suitable for the available space in the lockable box. is low cost uses switching technology. has a triple output(+15,-15 and5 VDC) can protect the circuit against short-circuits, over current and over voltage. Each transducer needs a supply voltage of ±15 VDC and consumes 10 ma plus the nominal output current which is 25mA, therefore each transducer consumes 35mA. In total, both Hall Effect boards, which contain a total of eight transducers, draw 280 ma current. In case the Hall Effect Boards require higher current, it is safer to select a power supply with higher rated current than 280 ma. The Mean Well T-40C has a different rated current for each output. For example the +15V terminal has a current rating of 1.5A, the -15 V terminal has current rating of 0.5 A, and the 5 V terminal has a current rated of 3 A. Basically, the +/- 15 V terminals have higher current ratings than 280 ma, which makes the power supply suitable for the system. Figure 3.14 shows the 40W T-40C power supply.( For technical specifications, see the data sheet in the appendix.) 30 P a g e Figure 3.14:40W T-40C ±15 VDC power supply

37 3.6.3) DC power supply Mean Well 60W S-60 This power supply is used to supply 24 VDC for the contactor relay, which is used for islanding tests. This power supply has a rated current of 2.5 A, 24 VDC and 60 W. It has a single output. This power supply is short circuit, overload and over voltage protected. Figure 3.15 shows 60W S-60 DC power supply. (For technical specifications, see the data sheet in the appendix.) Figure 3.15: 60W S-60 24VDC power supply 31 P a g e

38 3.7) Protection 3.7.1) Introduction This system, like any other electrical system has been equipped with protection such as a circuit breaker, residual current device and contactor relay. As mentioned before, the lockable box is a part of the grid connected PV system that has educational purposes and will be a part of lab exercises for students. Therefore, the system and especially the lockable box must be equipped with the maximum protection. In addition, the lockable box must comply with the Australian standards, from a safety point of view ) Miniature circuit breakers (MCB) The Circuit Breaker is an electrical device that is connected between source and circuit. It monitors and controls the amount of the current flowing into the wiring of the circuit. Circuit Breakers come in a variety of sizes, for example 10, 15, 20 and 30 amp. Circuit Breakers have two main categories: AC and DC. If a circuit breaker has been built for AC it can be used for DC or vice versa. Currently every new home has a Circuit Breaker in the main circuit board while in the older houses and buildings fuses are used. Fuses work very similar to the Circuit Breakers but Circuit Breakers are safer to use and easier to reset. [13] If a power surge occurs in the electrical wiring, the breaker will trip. This means that a circuit breaker that was in the "ON" position will flip to the "OFF" position and shut down the entire circuit that is connected to that particular circuit breaker. In fact, a circuit breaker is a safety device. When a circuit breaker is tripped, it may prevent a fire from starting in an overloaded circuit; it can also prevent a device from drawing excessive current. The Miniature Circuit Breaker 4CB106/6DC single pole has been selected for the system (figure 3.16). This Circuit Breaker will trip if there is any fault in the system. It has 6 ADC rated current and 250 VDC voltage. Four circuit breakers have been used to protect the lockable box from overcurrent. Two of these circuit breakers are installed between the PV modules and inverters. These two circuit breakers must be DC rated. The other two must be installed after each inverter and must be AC rated. 32 P a g e

39 Figure 3.16: Miniature circuit breakers (MCB) Figure 3.17 shows how the circuit breaker is connected in the circuit. The circuit breaker is connected between the PV module and the circuit. The Live wire is connected to one terminal and load to other terminal. The Neutral is not required to be connected to circuit breaker. A PV module N Terminal 3 AMP 1 A Figure 3.17: Wiring diagram of Miniature circuit breakers (MCB) 33 P a g e

40 3.7.3) Residual Current Devices (RCD) RCD s, or safety switches, are required for hand-held electrical equipment, portable electrical equipment that operate from sockets and for the power points of all new and old houses according to electrical regulations. The RCD that has been used for the local load is CLIPSAL model 4RCBM210/30, which combines Miniature circuit breakers (MCB) within an RCD or safety switch. It is rated 10 A current and has maximum tripping time of 40 milli-seconds. Figure 3.18 shows CLIPSAL model 4RCBM210/30 RCD or safety switch and figure 3.19 shows the wiring diagram of the RCD. Figure 3.18: RCD or safety switch Figure 3.19:Wiring diagram of an RCD or Safety Switch 34 P a g e

41 3.7.4) Contactor Relay A contactor is an electrically controlled switch used for switching a power circuit. A contactor is activated by a control input, which is usually a low voltage (12/24 VDC) DC power supply. Contactors are used to control motors, lighting, heating and other electrical loads. Contactors consist of three main parts, as follows: A contactor system, that carries the current An electromagnet system, that provides the driving force to close the contacts An enclosure system, that provides a frame and insulation for the contact and electromagnet. Figure 3.20 shows the contactor relay. Figure 3.22 shows how the contactor is connected in the circuit. Figure 3.20: Contactor 3.7.5) Islanding Switch (MOLLER T ) This switch has been selected because it allows the students to conduct the islanding test. This switch will increase the safety within the system circuit and will make the islanding test possible. Figure 3.21 shows the switch (MOLLER T ) and figure 3.22 shows how it is connected in the circuit. 35 P a g e

42 Figure 3.21: islanding switch Figure 3.22: Contactor and switch wiring diagram 36 P a g e

43 3.7.6) Test points (4mm connection and BNC- Bayonet Neill Concelman) After the system is completed, it will be a part of student lab exercises. Therefore, the lockable box must be equipped with test points that allow the students to measure the currents and voltages on AC and DC sides of the inverter. They must be able to observe waveforms on the oscilloscope and observe,measure the islanding phenomenon. The important point about these measurement points is safety. Two different connections have been selected (4mm connection and BNC connection) and both are safe for students to use. As it can be seen in the figure 3.23, these test points are installed on the front cover of the lockable box. Figures 3.24 and 3.25 show how these points are connected to the system. Figure 3.23: Measure points which consists of 4mm connections and BNC connections Figure 3.24: Measure points for DC voltage and current 37 P a g e

44 Figure 3.25: Measure points of AC voltage and current and islanding test 38 P a g e

45 3.8) Independent Grid-Connection 3.8.1) Introduction Connecting the system to the grid requires that the system complies with the Australian Standards. Because this system has educational applications and students will be required to measure DC / AC voltages and currents, this system will not comply with the Australian Standards because of the included measuring points. Martina arranged an appointment with Hari Sharma from RISE and we met with him to discuss this issue and to find other available options in order to connect to a system that acts like a grid. We came up with three options, which could replace the grid, they are: a small AC source (6813B AGILENT) a diesel generator a stand-alone PV system with battery backup 3.8.2) AC source (6813B AGILENT) AGILENT 6813B AC power source (figure 3.26) is an option that can replace the grid. This AC power source has maximum power of KVA, maximum voltage rms of 300V and maximum current rms of 13A. This power supply is usually used for testing. This particular power supply is equipped with a power amplifier and arbitrary waveform generator, which makes it an ideal device for a test bed. (For more information, see the data sheet of AGILENT 6813B AC power supply in the appendix) Figure 3.26: AGILENT 6813B AC power supply [14] 3.8.3) Diesel generator Diesel generating sets are usually used in remote areas that are too far from electrical utilities. Diesel generators can also be used as an emergency power supply if the grid fails. The size of small generators (portable) range from 1KVA to 10 KVA, while the larger size or industrial generators can range from 8KVA- 2000KVA. Sizes such as 5MW are used for small power stations. Diesel generators are also used during peak periods or when there is a power shortage in order to feed power into the grid. [15] 39 P a g e

46 Generator sets are selected based on the load they intend to supply power for. Other factors such as continuous power and size of the load are also very important ) Stand-alone PV system with battery backup Stand-alone PV systems are designed to operate independent of the electrical utility grid and are generally designed for specific DC or AC loads. Stand-alone PV systems can operate alone or they can operate in conjunction with diesel or wind turbines. This type of stand-alone system is called a PV hybrid system. The stand-alone systems can be categorized as follows: Direct coupled system: In this type of system, the load is directly connected to the PV array. Figure 3.27 shows a block diagram of a direct coupled. Figure 3.27: direct coupled PV system. Stand-alone PV system with batteries: This type of system is able to store energy in the batteries and then the load is able to use these energy when PV arrays are not generate sufficient power. Usually these systems are used when load requires continuous power. Figure 3.28 shows the stand-alone system with battery storage. Figure 3.28: stand-alone PV system with battery storage Hybrid system, when a stand-alone PV system is used in conjunction with a diesel generator or a wind turbine. Figure 3.29 shows a hybrid system. 40 P a g e

47 Figure 3.29: hybrid system 41 P a g e

48 3.9) Islanding Test Procedures 3.9.1) Islanding test Procedures Islanding tests are one of the main application objectives of this system. Therefore, this report must include the proper instructions for conducting the islanding tests. In addition, wiring diagrams of the islanding test can help the students to realise how islanding tests are set up and how they work. To perform the islanding test students can follow the steps give below (assuming that the PV module and grid are connected): 1. Connect channel one of an oscilloscope to the Plug&Power inverter test point and channel two to the islanding test point. On channel one, the voltage of the inverter can be observed which is around 2.5 V AC. (The Hall Effect Sensor converts the 240VAC to 2.5 VAC approximately.) On channel two, 24VDC can be observed. This voltage indicates islanding test contactor.(24 VDC contactor closed, which means the system is connected to the grid; 0V contactor open means that the system has been disconnected from grid). 2. The islanding test switch, Switch 1 (SW1) must be set to open state (0). 3. In this stage, you must wait until the inverter feeds into the grid and current is displayed at the output of the inverter. 4. When SW1 is closed (islanding switch set to 1) the test is carried out. Figure 3.30 shows the islanding relay, islanding switch, islanding test point and 24 VDC power supply for energising the islanding relay. 42 P a g e

49 Figure 3.30:Islanding test circuit The islanding test has been performed with a similar system and conducting the islanding test on this proposed system shall produce results very similar to the results of this test. This test was conducted in ENG 421(Renewable Energy System) for the islanding test on the Plug and Power inverter (Pacific Solar inverter). In this test, we can compare the results of the test with the Australian Standard If the test complies with AS/NZ then the inverter can be accredited, otherwise it is not safe to use the inverter due to islanding issues. [16] 43 P a g e

50 3.9.2) Results Figure 3.31 shows the sinusoidal waveform of the inverter (Plug&Power) on the channel one and 24VDC from the contactor on the channel two. T T 1) Ch 1: 100 mvolt 10 ms 2) Ch 2: 20 Volt 10 ms Figure 3.31:Waveform of the inverter and 24vdc from contactor Figure 3.32 shows the islanding test result with 11-Watts fluorescent light load. As it can be seen from the figure, the period of time before the voltage returned to zero, or inverter turns off, is about 70 ms. T 1) Ch 1: 100 mvolt 25 ms 2) Ch 2: 20 Volt 25 ms Period that voltage returns to zero Figure 3.32: voltage waveform with 11W load 44 P a g e

51 Figure 3.33 shows the islanding test result with a 349 W load. In this case, it takes 10mS to turn off the inverter. T T 1) Ch 1: 100 mvolt 10 ms 2) Ch 2: 20 Volt 10 ms Period that voltage returns to zero (10 ms) Figure 3.33: voltage waveform with 349W load The results were satisfactory: according to the AS/NZ the inverter must be disconnected within 2 S. The inverter has been tested under two different load conditions with results that comply with AS/NZ [16] 45 P a g e

52 3.10) Lockable Box Design ) Introduction The lockable box is a part of the grid connected PV system, which will be installed in the OTA (Outdoor Test Area) at RISE by the school of Engineering. This system is intended to be used as part of lab exercises for students in the Renewable Energy Engineering Degree ) Lockable Box The Lockable box has been divided into two parts; the first part is inside the box which is known as a lockable box (Figure 3.34) and the second part is the front cover or display panel that we will also look at (figure 3.37). The lockable box consists of following devices: One Plug&Power (Pacific Solar) inverter One OK4E-100 inverter One Hall Effect Board for DC side One Hall Effect Board for AC side One Relay contactor One +/- 15 VDC power supply One 24 VDC power supply Figure 3.35 shows the design of the lockable box and the location of the components in the lockable box. Figure 3.36 shows the completed lockable box with all components installed inside. Figure 3.34: Lockable box 46 P a g e

53 Figure 3.35: Location of the components inside the lockable box 47 P a g e Figure 3.36: lockable box with all components installed inside.

54 3.10.3) Display panel The front cover of the lockable box is known as a display panel (Figure 3.37). It acts as the test centre, which students are able to measure the DC and AC voltages and currents and capture the waveforms on an oscilloscope. In addition, students are able to test and experience the islanding phenomenon from there. The Display panel consists of the following devices: Four Miniature circuit breakers (MCB) One Residual Current Device (RCD) Test points One power point Four analogue current meters Two analogue Voltmeters One switch Figure 3.38 shows the design of the display panel and figure 3.39 shows the locations of the components on the display panel (The design of the display panel was handed to RISE and waiting for approval) Figure 3.37: Display panel (Front cover) The figure 3.38 shows the design location of the devices that must be installed on the display panel. 48 P a g e

55 Figure 3.38: Location of the device on the display panel Figure 3.39: Location of the device on the display panel 49 P a g e

56 3.10.4) Wiring diagram of the lockable box,display panel and determining cable size Figure 3.40 shows the wiring diagram of the lockable box and display panel. This wiring diagram has been handed to RISE for approval. The wiring diagram and mechanical drawing Australian standard 5033 is used. [17] Figure 3.40: Wiring diagram of the lockable box and display panel Table3.1 shows the size of the cables in the lockable box. Table 3.1: Size of the cable used in the lockable box 50 P a g e

57 Chapter 4 Hall Effect board test results 4.1) Introduction Current and voltage transducers are the main part of the Hall Effect board but before installing them on the board, each one of them must be checked for output signal and linearity. The main purpose of the Hall Effect is to display the waveforms, but it is advisable to check the linearity of transducers because it will help to determine the output of the current and voltage transducers when they are installed on the board. This chapter will investigate the test procedures of the voltage and current transducers and the Hall Effect board. In addition, it will identify the test circuit for each individual test and the equipment needed for conducting the test. 4.2) Test the current and voltage transducers for linearity with DC voltage This test is conducted to assess the linearity of the current and voltage transducers. This test will identify what can be expected at the output terminals of the each transducer with respect to the input voltage and current ) Method and Materials Figure 4.1 shows the test circuit for the current transducer. Figure 4.2 shows the test circuit for the voltage transducer. In both tests, a DC power supply has been used to supply the DC voltage, which is taken as an input signal for the transducers. As it can be seen in figure 4.2, the voltage transducer test circuit does not have a load but in the test circuit of figure 4.1, the current transducer requires a load because the current transducer needs to be connected to the circuit in series. 51 P a g e Figure 4.1: Test circuit of the LA25-NP current transducer

58 DC power supply +/- 15 VDC power supply Signal to be measured - + DC Power supply COM R1 +HT + - -HT + LV 20-P - M Is RM=100 Ohm Multi Meter Figure 4.2: Test circuit diagram of the LV 20-P voltage transducer The equipment used within these test circuits is listed below: Current transducer The current transducer that has been used for the Hall Effect board is an LA 25-NP (see figure4.3). The input current of this transducer is between 0-36 A but it depends on the input terminal s connection configuration. For example, for a nominal primary current of 5 A, the voltage drop across pin 1 and pin 6 must be measured while the rest of the pins are connected in order; pin 2 to 10, 3 to 9, 4 to 8 and 5 to 7. As shown in figure 4.3. (For more details, see appendix in the current transducer data sheet). Pin number 6 Pin number 1 Figure 4.3: Current transducer LA 25-NP 52 P a g e

59 Voltage transducer The voltage transducer selected for the Hall Effect board is an LV20-P (see figure 4.4). This voltage transducer has an input current rated at 0-14 ma. Therefore, this is the main reason for having the input resistor (R 1 ). This resistor will limit the current to less than 14 ma. (For more details, see appendix in the voltage transducer data sheet). Figure 4.4: voltage transducer LV 20-P 4.2.2) Calculating the voltage transducer input resistor: To calculate the value of R1, I assume the maximum input signal of 45VDC and an input current of 10 ma. The following formula can be used to find the value of R 1.. = I P is primary current V in is nominal voltage to be measured R 1 is the input resistor of voltage transducer = = 4500 DC power supplies This test requires two DC power supplies; one of them is used as a measure signal (input signal) and the other one supplies ±15 VDC to transducers. More details are given below: 1. ESCORT 3030TD Figure 4.5 shows the ESCORT 3030TD power supply; this particular power supply has a variable voltage range. In addition, it is able to supply a maximum 53 P a g e

60 of 60 V DC if connected in series and maximum of 6A current if connected in parallel. Figure 4.5: ESCORT 3030TD power supply 2. +/- 15 V DC power supply Figure 4.6 shows +/- 15 V DC power supply; this power supply is used to supply +/- 15 V for transducers. Maximum current rated of this power supply is 1A. Figure 4.6: +/- 15 V DC power supply Two digital multimeters: These digital multimeters are used to measure the voltage and the current of the circuit. Their main purpose is to measure the voltage at the output terminals of the transducers. In the stage of each individual test, the multimeter should be connected in series in circuit as it can be seen in figure 4.1 and 4.2. Figure 4.7 shows the type of the multimeter that has been used for measurements. The accuracy of is MIC 39 TRUE RMS is 0.5% +5 for the voltage between 4-400V AC. 54 P a g e

61 A B Figure 4.7: Digital multimeter (A) DIGITECH QM1300 (B) MIC 39 TRUE RMS Variable resistor (rheostats): The test circuit for testing the current transducer requires a load because the current transducer must be connected in series in order to measure the current. So a proper load must be selected for the circuit so the test can be performed. The best available load was a variable resistor. When we have voltage and current, it is easy to work out the required variable resistor. The calculation has been shown below: According Ohm s law V= 45 V I=3 A So R=15 Ω but the nearer available variable resistor was 11Ω which is close enough to perform the test. Figure 4.8 shows the variable resistor, which has maximum of 11Ω and a maximum current of 5.2A. This variable resistor is suitable to use as a load for the testing circuit. The connection points of the variable resistor are in figure P a g e

62 Connection points Figure 4.8: Adjustable resistor (rheostats) Resistor R M Current and voltage transducers require a 100Ω resistor in the measure terminal, which limits the current. (For more details, see the appendix in the current transducer data sheet) 4.3) Current transducer linearity test procedures After the test circuit is connected as shown in figure 4.1, the DC power supplies can be turned on and start from zero volts. The multimeter that is connected in series within the output of the circuit shows the output current. The output signal can be read from that multimeter. Voltage and current should be increased step by step and every time the voltage and current change, the output must be recorded. 4.4) Voltage transducer linearity test procedures In a linearity test of the voltage transducer, the circuit should be connected as previously shown in figure 4.2. The voltage transducer test is similar to the current transducer test as it was explained in section 4.3. The test will start with signal voltage set to zero, then gradually the voltage should be increased and the output current should be recorded. 4.8) Test procedures of the DC Hall Effect Board 4.8.1) Introduction This test was conducted to check the performance of the DC Hall Effect board. In this test a DC power supply replaces the PV module ) Method and Materials The circuit of figure 4.9 shows the testing configuration for the Hall Effect board test. The circuit consists of following items: 56 P a g e

63 Figure 4.9: testing circuit configuration of Hall Effect Board 1. Hall Effect Board: Hall Effect board consists of two current transducers, two voltage transducers and a set of resistors. Current transducers are responsible for converting the current to lower level current so that the user is able to measure it on the multimeter or observe on an oscilloscope, but for measuring the current, the multimeter must be connected in series to the circuit, and in this case it is impossible. We should measure the voltage at the output terminal and by using the value of the resistor in the output calculate the current. Voltage transducers are responsible for converting the voltage to lower level voltage. Voltage transducer output will also be in the form of voltage. Therefore, by using output voltage and value of the output resistor, the current can be calculated. 57 P a g e

64 2. Two DC power supplies 3. Two Multimeters 4. Variable resistor (rheostats) Section 2, 3 and 4 have been describe in the previous test (see Transducers linearity test) I assumed that maximum voltage entering the Hall Effect board from the PV modules is 45 VDC and maximum current is 3A. However, the power supply is current/voltage limited, and the load (variable resistor) draws a lot of current therefore the voltage drops in the circuit. The voltage entering the Hall Effect board is only 36 VDC and current is 3A. Note: The 45 VDC and current 3A are selected because I assumed the maximum voltage and current that can be produced by a PV module is somewhere around these numbers. The test circuit and Hall Effect board require proper cable sizes to minimize the losses in the wiring. Therefore, I selected between available wires, which one was closest to the recommended wire. Figure 4.10 shows the cable size within the test circuit and figure 4.11 shows the cable size on the Hall Effect board. Conductor cross section area is 0.75 mm^2 current rating of7.5a Conductor cross section area is 0.14 mm^2 current rating of 1.5 A Figure 4.10: size of the cable for the testing circuit 58 P a g e

65 Conductor cross section area is 0.44 mm^2 Conductor cross section area is 0.14 mm^2 Figure 4.11: Back of Hall Effect Board and size of cable 4.6) Results of the linearity test on the transducers The results of linearity test on current transducer are recorded in the following table (Table 4.1). Finally, to observe the linearity of the current transducer output results can be graphed in Excel. Figure 4.12 shows the linearity of the voltage input versus current output and figure 4.13shows the linearity of current input versus current output. In both figure 4.12 and 4.13 the trendlines have been shown which makes it easy to compare the measured results with the linear trendline. (Red line is trendline) Voltage input (V) Current input(a) Current output (ma) P a g e Table 4.1: Voltage and current input and output current of current transducer

66 Current output(ma) Voltage input (V) versus current output (ma) Voltage input (V) Figure 4.12: linearity of the voltage input versus current output Current output(ma) Current input(a) versus Current output (ma) Current input(a) Figure 4.13: linearity of current input versus current output 60 P a g e

67 Table 4.2 shows the results of the linearity test on the voltage transducer, Excel was used to graph the results again. Figure 4.14 shows the measured output and a linear trendline, which makes it easy to compare between the output points and trendline of linearity. (Red line is trendline) Voltage input(v) Current Output ( ma) Table 4.2: voltage input and current output of the voltage transducer 61 P a g e

68 Current output(ma) Voltage input (V) versus Current Output ( ma) Voltage input(v) Figure 4.14: linearity of the voltage input versus current output As it can be seen in figures 4.12 and 4.13 for current transducer and figure 4.14 for the voltage transducer, the results have very good output linearity, as expected. 4.7) Results of the DC Hall Effect board test The results of the Hall Effect board are summarized in figure 4.15, which shows the measurement points at various locations on the DC Hall Effect board. 1. Voltage across the input terminals of the Hall Effect is 36.7 V and current is 3A 2. Voltage across the input resistor of the voltage transducer is 36.5 V. 3. Voltage across the input terminals of the voltage transducer is around 35.2 V. There is a small drop in the voltage, which is due to the resistor within the wiring circuit. 4. Voltage in the output terminal of current transducer is around 1.5V. (Current can be calculated by dividing the output voltage across the load output resistor) 5. Voltage across the output of the voltage transducer is around 1.8 V. (Current can be calculated by dividing the output voltage across the load output resistor ) 62 P a g e

69 Figure 4.15: Voltage and current in the different points of the DC Hall Effect board The results of the Hall Effect board, as it was discussed above, are very close to what was expected. The current transducer output is 1.5 V or 15mA for 36 V or 3A. This can be proven by comparing the result with the linearity graph (figure 4.13). The result for the voltage transducer is also what was expected and this can be proven by comparing the result with the voltage transducer linearity graph (figure 4.14). 4.8) AC Hall Effect Board test 4.8.1) Introduction This test was conducted to check the performance and functionality of the AC Hall Effect board. The AC Hall effect in the lockable box is responsible is converting the voltage and current on the AC side of the inverters to a safe level. This action allows students to observe the waveforms of the AC voltage and current on the oscilloscope in a safe manner. The objectives of this test are: Check the functionality of the Hall Effect board Check the linearity of the output versus input Check the conversion factors (estimate the input from output) Note: Due to use of 240VAC voltage, this test was a supervised test and it was performed under the supervision of Dr. Martina Calais. 63 P a g e

70 4.8.2) Method and Materials The circuit of figure 4.16 shows the testing configuration for the AC Hall Effect board test. The circuit consists of following items: DC Power supply com Grid connected 240V VARIAC N A 1 J8 Com MPC PS 1 J9 + - MPV PS 1J10 MPV OK4 1 J11 MPC OK4 1 J12 HEB AC side Voltage nuteral Current out Current in 1 J13 Voltage nuteral Current out Current in 1 J14 Multimeter Escort 3136A Multimeter MIC39 Ture RMS Ch2 Ch1 Oscilloscope Load Figure 4.16: Testing circuit configuration of AC Hall Effect board 1. Hall Effect board: Hall Effect board descriptions can be found under the section method and materials for the DC Hall Effect board test. The only difference between DC and AC Hall Effect board are the input resistors. On the AC Hall Effect board these resistors are selected to suite the AC voltage (22KΩ 5W). 2. VARIAC ( variable voltage transformer non-isolating): VARIAC is a device that is able to provide AC voltage in a variety of levels. This particular VARIAC has a voltage rage of V and maximum current of 2.5A. 3. DC Power supply: 64 P a g e

71 ESCORT 3030TD is a power supply that is used to provide the ±15 VDC supply voltage to Hall Effect board. Figure 4.5 shows an ESCORT 3030TD DC power supply. 4. Multimeters: Two different multimeters are used to measure the current and voltage that enter the Hall Effect board. The ESCORT 3136A measures the current and the MIC 39 True RMS (figure 4.7 B) measures the voltage in to the Hall Effect board. 5. Tektronix TDS 1002 Oscilloscope: The oscilloscope used to observe the waveforms and measure the output signals. 6. Load : The load consists of a set of incandescent (two 60W and two 100W) and fluorescent (one 11W and one 18W) bulbs. By switching on or off, it is possible to change the load. The AC Hall Effect board was tested under different AC voltages and loads. The output signals, which were displayed on the oscilloscope, can be observed and measured. One of the reasons that the AC Hall Effect board was tested with different voltages and loads is to check the performance of the Hall Effect board under different voltages and loads. The other reason is to have enough points to create a graph with the results and check the linearity of the current and voltage transducers output. 4.9) Results of the test on the AC Hall Effect board In this test, each transducer was tested separately and results of each transducer were recorded separately too. Figure 4.17 shows the AC Hall Effect board with the transducers. VT2 CT2 VT1 CT1 Figure 4.17: AC Hall Effect board 65 P a g e

72 The current transducers CT1 and CT2 were tested with different loads. The input voltage from the VARIAC was set to 240V and then by increasing the load in steps the outputs were recorded. This way the current transducers can be tested under different currents. The input currents were measured with an Escort multimeter. By referring to the Escort multimeter s data sheet the accuracy can be found and then uncertainty of the output values can be estimated.(see appendix 6.8) 4.9.1) Current transducer test The results of current transducer CT1 were as follows: Current in Voltage out (mv) Table 4.3: Output of the current transducer CT1 Figure 4.18 shows the graph of current transducer CT1. In this graph, input current is plotted versus output voltage. 0.8 Current in versus voltage out Voltage out (V) Current in (A) Figure4.18: Input current versus output current of CT1 current transducer 66 P a g e

73 Table 4.4 shows the results of the current transducer CT2. According to the data sheet, the output of the current transducer must be linear and figure 4.19 prove this statement. Figure 4.19 shows the input currents to the current transducer CT2 versus output voltages. Current in Voltage out (mv) Table 4.4: Output of the current transducer CT2 Current in versus voltage out Voltage out (V) Current in(a) Figure 4.19: Input current versus output current of CT2 current transducer 4.9.2) Converting the output signal to input signals (Current transducers) The setup used in a laboratory setting will not allow the students to measure currents and voltages on the input side of the AC Hall Effect board. Therefore, it is desirable to know the conversion factors between output signals and input values. The output signals of the current transducers are presented on the oscilloscope in form of voltage. However, the results can be converted in to current and this is possible by using the value of the output resistors on the Hall Effect board. (100 Ω) In the case of the current transducers, when the output current is present it would be possible to estimate the input current. According to the data sheet of the current transducers, the input current of 5A would have output current 25mA. Therefore, with 67 P a g e

74 respect to these information and output current the input current can be found easily. [7] (Appendix 6.1 current transducer data sheet) For example, for an output voltage of 346 mv the input current can be calculated as follows: For calculating the output current, we assume the output resistor is 100Ω. Therefore, the current is 3.46 ma. Then =.. X =.. = 0.692A input current Therefore, the input current in this case is 0.692A and the input current that was read on the multimeter is (See table 4.3) The calculated value of the input current is different to the value of the current that read on the multimeter that is due to the accuracy of the devices that have been used (Oscilloscope, multimeter and resistors). The accuracy of these devices are given in the data sheet. The uncertainty of the results can be estimated by referring to the accuracy of the measurement instruments used. (See appendix 6.8 for example). For example, if the measuring error of the oscilloscope for this particular measurement (346mV) is around V and then the output voltage can be between 0.319V and V. These values are the uncertainty of the output voltage on the oscilloscope. Then by using these values, it is possible to find the range of the corresponding input current. If the output is mV then the input current can be estimated at 0.638A and if the output is mv then the input current can be estimated at A. Therefore the input current can be somewhere between these values. The uncertainty of the output voltage was estimated based on given instrument accuracy; other factors can have effect on the reading of the output voltage (resistors). In this test, an oscilloscope was used to measure the output voltage but it is not recommended to use an oscilloscope for measuring the voltage at output. Oscilloscope can be used only for observing the waveforms and for measuring an Escort multimeter can be used. The percentage of the error for the above example is 7.6%. This error is due to low reading on oscilloscope and when the vertical position offset from the ground reference. These problems make the oscilloscope unreliable for measurement. 68 P a g e

75 4.9.3) Voltage transducer test Table 4.5 shows the results of the voltage transducer VT1. Voltage in (V) Voltage out(v) Table 4.5: Output of the voltage transducer VT1 Figure 4.20 shows the graph of the results in the table 4.7. In this graph input voltage are plotted versus output voltage. 3.5 Input voltuge versus output voltage Output voltage (V) Input voltage (V) Figure 4.20: Input voltage versus output voltage of VT1 In case of the voltage transducer, it is possible to find the input current and voltage from the output current. According to the voltage transducer s data sheet, the input resistor of the voltage transducer is used to limit the current. Therefore, if the input voltage is 220 V and the input resistor is selected 22KΩ. Therefore, the input current would be 10 ma and voltage transducer with 10mA input current would have output current of 25mA. These values can be use as a benchmark to calculate the input current. [9] (Appendix 6.2 voltage transducer s data sheet) For example, for an output voltage of 2.83V the input current and voltage can be calculated as follows: 69 P a g e

76 The current out can be calculated by using the output resistor (100Ω). Assumed that resistor is exactly100ω. Therefore, the output current is 0.028A. (Ohm s law) Then. =.. X=(0.01*0.028)/0.025= A To calculate the input voltage the Ohm s law can be use to find the input voltage *22000=246.4 V This value is confirmed by referring to table 4.5. As it can be seen, the input voltage of 240 is for output voltage of 2.83V. The uncertainty values of the output voltage also apply to the voltage transducers. In this case, (2.83V) the measuring error of instrument is and the output voltage can be between 2.49V and 3.16V. Therefore, the input voltage can be estimated between V and V. (See appendix 6.8 for more information) As it can be seen from the output voltage there is a huge difference between them and as it was mentioned before this is due to use an oscilloscope to measure the output voltage. Table 4.6 shows the result of the input voltages of the voltage transducer VT2. Figure 4.21 shows the graph of input voltages versus the output voltage. Voltage in Voltage out(v) (V) Table 4.6: Output of the voltage transducer VT2 70 P a g e

77 Voltage out(v) Voltage in versus voltage out(v) Voltage out(v) Voltage in(v) Figure 4.21: Input voltage versus output current of VT2 In brief, the objectives of the test on the AC Hall Effect board were 1. Check the functionality of the Hall Effect board 2. Check the linearity of the current and voltage transducers 3. Check the conversion factors (estimate the input from output) All these objectives were achieved during the AC test of the Hall Effect board. According to the data sheet, the current and voltage transducers have linear output; this statement was confirmed by graphing the input signals versus the output signals. The conversion factor was another aim of this test that it was confirmed by two examples. In addition the uncertainty of the output signals were estimated and then according to these values the input signals were calculated. Finally, the results of the test were satisfactory and complied with the data sheet. 71 P a g e

78 Chapter5 Conclusions and Future Work 5.1) Conclusions In brief, this project was a good challenge for me to assess my knowledge in different areas. In this project, I had to set up a box with the inverters, islanding relay, islanding switch, local load outlet, amp meters, voltmeters and protection devices. The final application can be used as a laboratory exercise for students in the Renewable Energy Engineering Degree. This system will be beneficial in the following ways: It allows students can get familiar with the characteristics of grid connected PV systems. It provides a safe environment for observing and measuring the DC and AC voltage and current waveforms on the oscilloscope. It has the ability to identify harmonics in the inverter output current It has the ability to perform an islanding test. To complete the project I faced many problems such as: Designing the Hall Effect Board Testing of the Hall Effect Board Designing the Lockable Box and Display Panel Islanding Test Realisation Documentation Integrating the system with an Independent AC source I designed and built the Hall Effect board and then tested it. Results from the Hall Effect board were satisfactory and my results were what I expected. In addition, I drew electrical and mechanical diagrams of the system and put the components together in the lockable box. The electrical drawing and cable sizes shall be sent to RISE for approval. 5.2) Future Work Although I intended to finish this project, I could not due to shortage of time. I could not complete the lockable box and the system is not ready to be installed within the main grid connected system (with connection to the PV modules and Grid). Therefore, there are some tasks of the project remaining and need to be completed in the future. These tasks are as follows: Conduct the test on the AC Hall Effect board. Wiring up the components in the lockable box. Installation of fans on the sides of the box for ventilation. Installation of the components on the display panel. AC source evaluation Conduct the complete test on the system 72 P a g e

79 6) Appendix 6.1) Current transducer data sheet Figure 6.1.1: Current transducer data sheet [7] 73 P a g e

80 Figure 6.1.2: Current transducer data sheet [7] 74 P a g e

81 Figure 6.1.3: Current transducer data sheet [7] 75 P a g e

82 6.2) Voltage transducer data sheet Figure 6.2.1: Voltage transducer data sheet [9] 76 P a g e

83 Figure 6.2.2: Voltage transducer data sheet [9] 77 P a g e

84 6.3) 24 VDC power supply data sheet Figure 6.3.1:24V DC power supply data sheet [18] 78 P a g e

85 Figure 6.3.2: 24V DC power supply data sheet [18] 79 P a g e

86 6.4) ±15 VDC power supply data sheet Figure 6.4.1: ±15V DC power supply data sheet [19] 80 P a g e

87 Figure 6.4.2: ±15V DC power supply data sheet [19] 81 P a g e

88 6.5) AGILENT 6813B data sheet Figure 6.5.1:AGILENT 6813B data sheet [14] 82 P a g e

89 Figure 6.5.2: AGILENT 6813B data sheet [14] 83 P a g e

90 6.6) Circuit breaker and RCD data sheet 84 P a g e Figure 6.6.1: Circuit breaker and RCD data sheet [20]

91 Figure 6.6.2: Circuit breaker and RCD data sheet [20] 85 P a g e

92 Figure 6.6.3: Circuit breaker and RCD data sheet [20] 86 P a g e

93 Figure 6.6.4: Circuit breaker and RCD data sheet [20] 87 P a g e

94 Figure 6.6.5: Circuit breaker and RCD data sheet [20] 88 P a g e

95 89 P a g e Figure 6.6.6: Circuit breaker and RCD data sheet [20]

96 Figure 6.6.7:Circuit breaker and RCD data sheet [20] 90 P a g e

97 6.7) Folder and file available on CD Folder File Description Hall Effect HES.vsd Wiring diagram of AC and DC Hall Effect boards, test circuits Inverters Inverter topology.vsd Topology of the gridconnected inverter Islanding test Islanding test.vsd Wiring diagram of the relay and islanding switch Wiring diagramsymbols.vsd Complete wiring diagram of the lockable box and 6.8) Estimating the measurement uncertainty when using the oscilloscope(tektronix TDS 1002 ) and the multimeter (ESCORT 3136A ) The measurement uncertainty of the oscilloscope can be estimated with following formula: (this formula is given in the data sheet of the oscilloscope). ± [3%* (reading+ vertical position) +1% of vertical postion+0.2div] If the settings are from 2 to 200 mv/div, we should add 2 mv to above formula. If the settings are from greater 200mV to5v/div, we should add 50mV to above formula. Figure shows the output waveforms of the current and voltage transducer on the oscilloscope. The vertical position and division can be identified on the figure CH1 current transducer CT1 Vertical position (2* 0.05V) Division 50mV (0.05V) CH2 voltage transducer VT1 Vertical position (2*2V) Division 2V 91 P a g e

98 Figure 6.8.1: Output waveforms of the current transducer CT1 (CH1) and voltage transducer VT1 (CH2) Following table shows the uncertainty value of output voltage of CT1 from oscilloscope. Voltage out (mv) Measurement error due to instrument (Delta v/voltage reading) (Voltage out) MIN voltage MAX voltage Delta V/V reading percent of the Delta V/Reading Table 6.8.1: Uncertainty results of the output voltage from the oscilloscope (CT1) Accuracy of the Escort multimeter is 0.5% +20 which the first number is given as reading percent and second number is least significant digit. This accuracy is for current range of 50 ma- 4mA and frequency of 50-2KHz. 92 P a g e