Implementing virtual laboratories: Remote teaching of electrical machines

Abstract

One of the fundamental requirements of engineering education is laboratory work and practical teaching. The main purpose of the laboratory is to provide a space for students to carry out practices that allow them to check the theory learned in the classroom, validate hypotheses, propose solutions and recommendations, develop critical thinking skills and develop soft skills. The provision of laboratory work to engineering students helps them familiarize themselves with similar situations as they will find real life as they practice their profession. Primarily, this laboratory work is based on actual hardware and a laboratory where the students can work at a specified time, perform experiments under the guidance of a lab technician and leave with data that they can analyze later using the knowledge they learned in class. These laboratories and the hardware equipment in them are expensive to acquire and maintain. Also, they are an expensive upgrade, yet upgrading is inevitable with the rapid change in technology we are all experiencing. Various institutions have been forced to use outdated laboratory hardware or do with minimal hardware for performing engineering experiments. However, the rapid increase in technology that is contributing to the problem can be used to solve it by having a suitable front-end design in computers that can be used to simulate experiments.

Keywords: Virtual laboratory, synchronous machine, optimization, simulation

1. Introduction: Virtual laboratories for teaching electric machines

One of the areas where virtual laboratory can be easily implemented is in teaching of electrical machines, which basically includes electric motors, transformers, and generators/alternators. This is mainly done in junior and mid-levels of electrical engineering programs across the world. Students carry out experiments to familiarize themselves with circuit parameters, losses in the machines, and the performance of the machines at various loading points. Usually, this is done with hardware equipment, which is expensive to upgrade and maintain. Also, this limits the time for students to carry out experiments on electrical machines. It can also lead to accidents in some instances. All these shortcomings call for the implementation of virtual laboratories and experiments. All that is needed is the experimenting platform and a local instructor to guide the students performing the experiment. This helps address the budget constraint and help educators provide effective education on electrical machines. The virtual laboratory should include an introduction for the students to electrical machines; induction motors, synchronous motors, synchronous generators, transformers, and special motors. This paper focuses on implementing a virtual laboratory for teaching electrical machine laboratory work [1-6].

Various virtual laboratories have been developed to enhance the remote teaching of electric machines, mainly transformers, induction motors, and synchronous motors. These laboratories solve the problems described above and make the teaching of electrical engineering students efficient. There are 3 main types of virtual laboratories mainly discussed in this paper, free virtual laboratories, the paid virtual laboratories, and our school-developed virtual laboratories. The virtual laboratory for our university, The National University of Colombia, is free as one does not need to pay to access its services [6-10].

2. Free virtual laboratories

2.1 LabVIEW-based model

Belu [1] proposed a virtual laboratory that could be used for testing different electrical machines like synchronous machines, induction motors, and the transformer. The virtual laboratory proposed would give these machines the characteristics and would offer a wide range of parameters, both from a physical lab setting and an industrial setting. In any virtual laboratory, there must be an interface that allows for the student's communication and the machine holding the virtual laboratory program. Students should be able to easily use the interface to perform their experiments and get results from where they can analyze them and develop a suitable report. The virtual interface proposed in [1] was accessible over the internet or web services. The interface had an embedded laboratory work on LabVIEW. However, unlike the case with both MatLab/Simulink and Labview software, where one has to install these files in their computer systems, this virtual lab environment executes easily on a web browser without the need for installing the software. There are various requirements in developing a virtual laboratory that suits the needs and demand of engineering educators and students, such as modularity, portability across multi-platforms, compatibility with hardware and software, debugging characteristics, standalone application, extendable libraries, graphical user interface, and high performance [1]. In this way, Belu [1] proposed a virtual laboratory that could be applied across all testing needs of electrical machined with all these characteristics.

2.2 Modelica-based model

According to Shi et al. [9], Modelica can be used as an internet-based electrical engineering laboratory. Though the claims are mainly focused on how this can be used be used in electronic laboratory, it can also be used in electrical machine laboratory, similar to Java. Modelica is suitable for electrical modeling and can therefore be suitable for modeling both complex and simple component circuitry. This means that a virtual laboratory on complex electrical machines connection includes its protection system, and relays can be easily modeled using this high-level object-oriented modeling language for physical systems. Modelica provides networking that can allow many users to access the customized electric machine virtual laboratory. Multiple users can access it through web browsers once the customized model has been developed and stored in a physical or cloud server. Educators can use this customized model to teach students about electrical machine laboratories by providing them with access to the model and guiding them on how to use the model in carrying out virtual testing of various electrical machines. This way, the students will know about the physical laboratory requirement and therefore familiarize themselves with the environment. However, this model has not been fully developed as the existing model developed by Shi et al. [9] was based on electronics. This means more studies have to be done, and developers have to work on developing the model and customizing it for the testing of electrical machines.

2.3 Java Ejs model

Casals-Torrens and Bosch-Tous [2] presented a virtual laboratory model for electrical machines based on Java Ejs (Easy Java Simulations). The Java Ejs is a free software tool that has been designed to favor the development of interactive virtual laboratories. According to Esquembre [4], this software offers high configuration and interactions of various visual elements, thus allowing for the model to be constructed faster and offer better views for the electrical machine laboratory. With the use of Java, the virtual laboratory model developed here would be accessible over the web or available for one to download and run on their personal computers. This enhances the usability of the model by students, and the ease of its adoption by educators as all they need to do is acquire it and allow the students to either install it on their personal computers or use it over the internet. The virtual laboratory developed here was found to have an approval rate of 52% of the users but could be further improved to gain a higher approval rate [2-4]. This virtual laboratory model's key features were its provision of three window graphics showing if the electric machine is on or off, the torque-speed curve, and the current density [2-4]. However, other than specifying the parameters and drawing the connected circuit, this model does not offer a 3D view of the machine, which limits its similarity to the real laboratory environment. This might be the reason it received a low approval rate from its users.

2.4 Virtual Labs in India

2.4.1 Shakshat Virtual Lab

A shakshat virtual lab is a tool for learning and experimentation made to allow people to share knowledge, data, voice, videos, and other resources. The agency provides an environment to extend, integrate, improve, refine and share expertise and experimental process of different subjects, contributing to an increase in the effectiveness of the scientific research and the scarce environment and equipment [5-7]. The virtual lab offers functions and tools that can be used when performing different simulations and experiments while one is controlling the overall environment and actions that he or she is doing.

2.4.1.1 Functions of the virtual lab

The main aim of the Shakshat Virtual Lab is to perform different activities such as load testing, speed controlee on the separately excited motor, blocked rotor test on three-phase induction motor, open circuit, short circuit, and load test on a three-phase alternator, No lead test, and open circuit testing.

2.4.1.2 Features of the virtual lab

• Magnetic field behaviors in single-coil. This part aims to study the generation of a field produced due to a single-coil using DC and Ac Current. Blocked rotor test rotating magnetic field with three coils- the main of this part of the virtual lab is to study the magnetic field produced due to three coils using an AC.

• The DC twist for stator resistance. This part aims to measure the DC resistance of the stator of the induction motor.

• The no-load test. The No-load test's leading-determines the no-load current I0 no-load power factor cost 0 friction losses and the input and no-load resistance R0 and reactance X0. The test is performed with different values of applied voltage below and above rated voltage.

• Stator resistance starter. The part of the lab is aimed at starting the induction motor by connecting the external rheostat to the stator winding.

• Star-delta starting aimed at beginning the induction motor using a 3-phase autotransformer.

• Auto Transformer-aimed at starting the induction motor by application of the star Delta starter.

The virtual lab contains different parts that any students can use to learn the simulator plays as the primary and essential parts of the virtual labs for electrical machines.

2.4.2 MHRD Indian Government virtual lab

The second virtual lab is from the virtual lab's platform by the MHRD Govt of India initiative. The virtual lab contains a different platform to do experiments in electrical machines that can perform various functions [5-7]. Just like the other virtual platform, the virtual lab contains the following parts:

• Aim of the platform

• Pretest for the students

• Simulator part that the students can perform different parts

• Audio and video part

• Reference and feedback section

Below are an example of the list of the experiments that the virtual land performs;

The virtual lab performs the following functions;

• Load test on separately excited DC motor- The main aim of the part is to stud or y the load test on separately excited DC mot

• Load Test on Three-phase Alternator- the main objective is to Study the Speed Control of Separately Excited DC Motor

• Short circuit test on three-phase alternator-To study short the circuit test on the three-phase alternator

• V and inverted V curves of synchronous motor- V Curves and Inverted V curves of Three Phase Synchronous Motor

• Blocked rotor test three-phase induction motor - The aim is to Study Short Circuit Test on Three Phase Alternator

With the virtual; lab all across India, students in different parts can study and use the available virtual labs to study the other learning objectives of the Electric machines. The students are also able to do simulations and do pretest and post test to know test their understanding [6-8]. With such a move the virtual labs will be able to provide the students with a conducive environment that both students and other engineers can use for the purpose of experimenting and preparing the labs hence reducing the time that is wasted in the labs and also promote hands-on skills for students who can't access the real machines. In general Virtual labs for electronic machines are the ideal training and experimenting environment for students and different researchers.

3. The National University of Colombia virtual laboratories

3.1 Induction motors and single-phase transformers

The National University of Colombia has developed a virtual lab for induction machines testing, the Virtual Induction Machine Laboratory (LVMI). Induction motors are very common in our world, with more than 80% of all motors in the industries being this type of motors. They have varied applications across industrial settings, and it would be important for students to familiarize themselves with these motors before they start their professional careers, whereby they will come across them more often. This virtual laboratory for induction motor was created in 2017. This LVMI was developed on the basis of the Virtual Laboratory of a single-phase transformer (LVTM) [5-7]. Transformers are also electrical machines having LVTM is a way of enhancing the use of the virtual laboratory for electrical machines within the university [5-7].

The virtual laboratory for the National University of Colombia helps the students familiarize themselves with these electrical machines before using the physical laboratory [5-7]. Through this, the use of the virtual laboratory for learning about electrical machines helps prevent accidents by familiarizing the children with an ideal working environment. At times, the laboratory work such as testing might need extra care since it might be harmful and might lead the students to accidents if not handled well. Once the students have done prior laboratory work using the virtual laboratory, they will familiarize themselves with the working environment and will definitely be at ease in performing the physical experiment.

The LVMI is mainly used for testing induction motors. Induction motors need optimum conditions to operate effectively, and therefore the knowledge on testing for the motors is extremely important. Two types of testing these motors are provided by the LVMI, the locked rotor test, and the vacuum test. These two tests are allowed by the LVIM, and students can easily carry them out virtually as they prepare to carry them out physically in the university laboratory. Students usually use the LVMI to creating the test connections. The LVMI also allows them to take measurements. As decreased above, LVMI is free and open for the public whereby it has a link which is open to the public; http://168.176.60.11/cursos/ingenieria/electrica/ [5]. Students can use this link to download the LVMI software and a manual to guide their work (Figure 1).

Figure 1. Virtual connection for testing virtual laboratory

Students have connected the motor under testing to the protection panel and the network analyzer in the above diagram. The network analyzer is seen to the right of the picture and the protection panel to the center [5]. Like any other electrical equipment, one should know that the induction motors need to be protected against surges in currents and voltages in the supply system. The protection system includes the use of current transformers, as seen above. Usually, various systems like the potential transformer and a relay system will need to be provided, but for this can, one can only see the current transformers which read the current flowing into the motor and identifies overcurrent, which might call upon the relay to act and to switch the motor off to avoid burning of the motor circuitry. The same can be applied for the locked rotor test, though for this one, the rotor will have to be held in position by breaks to ensure that it does not rotate.

The virtual laboratory setting using LVMI helps educators reach all students, even those with disabilities, and enhances their understanding of various induction motor testing. However, the students also need to carry out the physical laboratory work to meet the real-life induction motor. This virtual motor offers a controlled environment of testing, which is often different from a real-world testing environment. As such, educators and students teaching electrical machines using this laboratory need to be informed that they should also make an effort to carry out physical laboratory work and only use it as an extension.

3.2 Synchronous and Iduction machines laboratories

The third type of commonly used electrical machine is the synchronous machines, which is mainly applied in alternators and in some motors, especially those used for power factor correction. The National University of Colombia also provides a virtual laboratory for synchronous machines. According to Ramírez-Romero et al. [7], these labs are important to the learners as they allow them to familiarize themselves with the connection of power from a protection panel. Also, through the laboratory work on these machines, students know how to wire and operate a synchronous machine. Usually, the VLSM has a simulator that provides similar physical characteristics to those of a real synchronous machine, thus familiarizing users with what they are to find in industries and power stations using these machines. With the help of the VLSM, students end up practicing how to get data from a real synchronous machine [7].

The development of the VLSM was done in four phases; the analysis phase, the design phase, the development phase, and the implementation phase [7]. The first step mainly focuses on the knowledge of the synchronous machine laboratory. The second step focuses on the determination of the characteristics of the simulator. The third phase is very important and focuses on the coding of the similar to meet the characteristics determined in phase 2. Finally, the similar that has been coded is implemented, and manuals on how to operate it are published [7]. This development phases can be started all over again following the feedback given by the users. This allows for new features to be presented and in the improvement of the whole system. The same process of developing the VLSM was applied in developed both LVMI and LVTM. This is the latest development of the virtual laboratory for electrical machines from the National University of Colombia (Figure 2).

Figure 2. Induction virtual laboratory

Electrical engineering educators can easily use the VLSM to guide their students in performing laboratory work on synchronous motors. This is enhanced by the provision of the simulator in 3D. With this, the synchronous motor looks very similar to the ones students will encounter in the physical laboratory or in their professional career. This makes learning enjoyable for the students and makes it easy for them both in their professional careers and in conducting physical experiments. However, like in the other machines' virtual laboratories, educators have to be informed that the use of VLSM should not act as a replacement for the physical laboratory but mainly works to make it easier for students to use the physical laboratories and avoid incidents through familiarization of the laboratory environment and the electrical connections.

4. Paid virtual laboratories for electrical machines

4.1 MATLAB/Simulink model

Djeghloud et al. [3] proposed the use of MatLab and its Simulink package for electric machines in coming up with a virtual laboratory for electrical machine testing. MatLab is a software tool that contains packages that can be customized and used in virtual laboratory testing of electrical machines. This tool provides a wide range of engineering packages ranging from electronic, mechanical, and chemical engineering packages. Also, MATLAB provides a package for machine and deep learning. MATLAB is software that one has to buy its license in order to use it. However, Petropol-Serb et al. [8] provided customized simulated models and automated diagrams from MATLAB/Simulink that could be used for the provision of a virtual laboratory for the commonly used electric machines. The machines presented in their research include single-phase transformer, synchronous machine, induction motor, and Direct Current (DC) machines. The model developed in this case is not free as one needs a MATLAB/Simulink enhanced platform, and they can get it set up and used for teaching electric machines virtually. MATLAB is not free software, and one has to source it. This means that this model is a paid virtual lab model other than a free one. Educators using this model are encouraged to use it as an enhancement of physical laboratory work and familiarize students with electric machine laboratory work. This helps enhance their safety in performing electrical laboratory work, which can be classified as high-risk laboratory work, especially with high currents and high speeds of the rotor in both motors and alternators.

Shi et al. [9] also proposed another Induction Motor virtual lab model based on the graphical user interface (GUI) of MATLAB. Unlike the commonly used Simulink, MATLAB GUI can offer computational modeling of synchronous machines. This information can be tapped into to offer behavioral information on changing parameters, which is all an electrical machine laboratory work will be all about. With this, one ends up getting more information and better understanding of electrical machines [8-9]. However, this model is paid since it is based on MATLAB, which has to be paid for before getting its license and using it. Also, this model is tedious since it involves too many computations, unlike the use of the Simulink model described above. Also, the model is only based on induction/asynchronous motor, yet this is only one of the several types of electrical machines. The model is not the best option out there and has not been adopted widely due to these shortcomings.

4.2 Electromechanical Systems Simulation Software (LVSIM-EMS), from FESTO

The electromechanical software is a virtual simulation lab in which images of the actual EMS modules replace all the standard EMS laboratory equipment. The main aim of the EMS lab is to ensure that students can manipulate the different electromechanical systems on a computer screen. Additionally, the students have access to equipment that they have no physical access to. In such a computing environment, students using the EMS software can identify different equipment’s for any given exercise that they want to carry out and also make all the necessary connections between the modules that the virtual lab has passed and also verify if the link is good [7-10]. The software contains all the modules that the students may need, including the power supplies, motor generators, transformers, different electrical and mechanical loads, etc. Such modules are all simulated in the LVMIS –EMS software in the same panel in the software. With a friendly and straightforward User interface, the software is easy to use and close to many students.

The LVSIM EMS virtual equipment is a good representative of the actual EMS equipment available physically. The LVSIM- EMS helps many students develop hands-on skills on these different electrical types of equipment with the essential equipment available. Additionally, with the use of the Virtual lab, the students who use the virtual lab can also develop and prepare a lab in advance by understanding where to put different items in the lab [7-10]. This involves making connections required in the exercise, validating the links, saving, and finally printing the setup to prepare the actual design. With the Virtual preparation, then time wastage for the physical; lab setting is reduced, and much work can be accomplished without much struggle. Preparations of the physical lab using LVSIM-EMS cost-effectiveness are maximized.

The main features of the virtual lab

The LVSIM-EMS contains five main features which can be used for simulation purposes.

1. One metering window- the metering window displays 18 meters which can be sued for measuring AC/DC voltage, electrical power, speed, mechanical power, etc. Value, Crest factors, and particlu8er harmonic value. Six out of the available meatier can be programmed and access other functions that the user wants to use.

2. Oscilloscope- The oscilloscope displays up to eight waveforms simultaneously where each of the eight waveforms is of a different color which enables s the user to identify them quickly.

3. Phasor analyzer- it displays phases related to the voltages and currents that are required. The phase analyzer also shows the amplitude and phase angle of each voltage and the corresponding Phasor, which help display parameters in unique and dynamic displays of the voltages and circuit, which are very hard to obtain in conventional instruments.

4. Harmonic Analyser- The harmonic analyzer's main aim is to analyze the harmonic competes in the measured currents and voltages.

5. Data table and graph window- the data table records the values found in the metering window. The values are recorded in the data tables, which allows the results to be plotted easily, and more sophisticated graphs are created.

Features and benefits of the virtual lab                             

As earlier seen, the virtual; lab is a replica of the actual lab environment for electrical and mechanical engineering students. Students can p-perform actual experiments using the system; the students are able to perform the following activities in the EMS.

• Install the Ems modules in their workstations

• Modify or remove the virtual EMS in their workstations and also hanged the colors of the wires used

• Verify the module connections using different tools that have been provided by the system which include devices such as wires which may be connected to the same circuit

• Installation of timing belts between the two EMS machines

• The students can also measure voltage power, speed, torque, resistance, reactance, and frequency

• Record the measure of data in table and plot graphs using the recorded data

• Display different waveforms in the multi oscilloscope[e and ac voltages

Additionally to the stated functions, the students can also prepare the laborites in advance using the virtual environment from the EVMS. By using the virtual lab, there is a decrease in the amount of capital required to purchase the actual items by the students. Students have plenty of time to perform and practice with the EMS without the fear of destroying the physical instruments.

5. Conclusion

Electrical machines are an important aspect of our daily lives. We always use them everywhere, starting from the elevators we use to the simple phone chargers we use to charge our phones. These chargers contain transformers, which are part of electrical machines. Due to this extensive use of electrical machines, electrical students have to familiarize themselves with the machines while still in colleges and universities to enhance their prowess when they become practicing professionals. Educators for electrical engineering have to offer laboratory work to the student to ease their hands-on skills and familiarization with the real-life electrical machines found in the industries. The changing technology and high cost of the laboratory equipment required to carry out electrical machine laboratory work call for the use of virtual labs. These labs help to cover the technology gap and the high-cost equipment need. Also, it helps safeguard the students and familiarize them with the physical laboratory environment.

The advancement in software development has enabled the provision of various virtual lab model, some of which are free and other have to be paid for. Free virtual laboratory for electrical machine laboratory includes the LabVIEW-based model, the Modelica-based model, and the Java Ejs model. There are also specified free models for The National University of Colombia that include VLSM, LVMI, and LVTM for the synchronous machine, induction motor, and single phase transformer. Finally, there are paid virtual laboratory models which are based on MATLAB, which is non-free software. All these models provide educators with a virtual laboratory environment for electrical machine laboratory work. Though there are numerous virtual laboratory models for electrical machine, there is need of further research to develop other models which are more efficient and effective than this.

It should be noted that virtual laboratories are a didactic complement that can help to advance in the achievement of the learning objectives of some subjects, especially in forced conditions of virtuality. However, it cannot be considered a substitute for practical subjects based on laboratory experiences.

References

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