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Abstract- In a competitive world such as ours, students must be prepared beforehand to be autonomous, industrious and skilful. Problem-based learning (PBL) is a methodology that can help them explore and put to use their own resources, and it can be applied to a wide range of students and subject matters. Problem solving is introduced to the students by means of a 'design and make' project, engaging them in the process and making them aware of the design evolution. The project incorporates aspects of electrical engineering and computing skills. This study is dedicated to the learning process to help students to deal with the complexity of an electric power network. This approach benefits the motivation to learn, the students' self-esteem and improves the classroom environment. This study has conducted a new methodology in educational research by adopting technology for teaching and learning. In the Department of Electrical Engineering, preference was given to applying methods integrating technology in the learning and then evaluating the outcomes. PBL, as an instructional strategy of active learning, was used and adapted for use in Analysis in Electrical Power Systems programme. In cooperative learning, students work together in small groups in an organized way, on a well-ordered activity. They are individually responsible for their work; on the other hand, the work of the group as a whole is also assessed. Teams need to be small enough so that everyone can play a part. And the students' work must be clearly defined. By applying PBL it is expected that students work in a cooperative and collaborative learning way, developing positive interdependence, individual accountability, face-to-face promotive interaction, as well as group processing. PBL with students working in groups on real problems generates enthusiasm. Students see the potential of the method. PBL addresses many of the concerns of teachers and professional organizations. Above all, it encourages students to be in charge of their education. It emphasizes critical thinking skills, understanding, learning how to learn, and working cooperatively with others. The benefits of PBL in the Electrical Power Systems course are seen in the way students improved the study and analysis of the security in an electrical power system. This method can also be seen as a benefit for Electric Power Systems where educators strive for improved teaching and learning.
This paper describes how the module of Analysis in Electrical Power Systems (ASE 1), in the Department of Electrical Engineering (DEE), was utilized to engage students in the use of problem based learning (PBL). As these programmes require previous learning experience and an amount of background knowledge, students need to be motivated and encouraged to become responsible for their own learning.
PBL is an instructional method that challenges students to learn, working cooperatively in groups to look for solutions to real-life problems. Problems are used to connect students' interest and initiate learning in the subject matter. PBL prepares students to think critically and analytically, as well as to find and use appropriate learning resources. It is a powerful classroom process and a strategy that promotes life-long habits of learning. An important component of PBL is that the contents are introduced in the context of complex real-life problems. With PBL students, working in small groups, must identify what they know, and more essentially, what they don't know and must learn to solve a problem. This is the basis for understanding the problem and making decisions required by it. The most important role of the teacher is to facilitate group process and learning, not to supply easy answers [1-5]. Cooperative groups work face-to-face and learn to work as a team. In order to create an environment in which cooperative learning can take place, students need to feel secure, but also challenged [6-7].
This approach was supported by using messenger and e-mails interchanges among members of the same team, and between the team coordinator and the professors. Learning defines a dynamic process where the students work in closer contact with teachers, using the software package PowerWorld 11.0, for teaching and research purposes of the security analysis assessment of an electrical power system , . The main purpose of the software package is to provide the students and the researchers with an easy security analysis tool that allows modeling any power system component with the desired complexity. This case study describes the experience of three teachers with their class along a semester using computer aided technology for instruction and assessment. The most important part of PBL is an appropriate problem which comes from the real world and has a relationship with the course.
PBL is a dynamic process in which the students work in teams accomplishing a common goal.
It is expected that the project work enables students to:
Look into a problem, classify and divide it into its essential parts and perceive the knowledge required to be used in a new context.
Make use of an interdisciplinary approach to describe the solution for electrical design problems.
Show ability to plan and control the different stages and progress of group work.
Tackle engineering problems resorting to the system/method of 'thinking and describing'.
Along the project, students worked in groups of four to develop the desired learning skills, motivation and assessment. The whole class (31) was supervised by three staff members. All students had access to experimental, test as well as computing facilities.
Throughout the semester, students are expected to learn the design of the required test power network; to do the research and the evaluation of the system severity indices; to perform the study of the system security using the PowerWorld software package, for the given test power network; to make the analysis of the security of the test power network and determine the most suitable methodology flow and prepare the presentation and the documentation of the project. Students were also required to evaluate the post contingency steadyâ€‘state scenario in order to detect operational problems as well as to classify the power network status in accordance with its security level.
The project task
The project in (ASE 1) is developed along the first semester of the fourth year. The students are informed about the general outline of the project but are not given any specific details regarding the design or problem solving processes although they are made aware of the assessment process and resources available.
The Electrical Power Analyses programme teaches and establishes the basic concepts and techniques of the study and analysis of electrical power system steady-state security, in real time operation, to electrical engineering students. Therefore, this course has to cover vast areas of electrical engineering, though the workload for students is controlled. It is, for that reason, extremely important to carefully design all aspects of teaching and learning in order to improve the quality of the course.
It was designed a real world problem which will cover most of the content of this course. Each of the team members were given specific tasks, in the team, towards achieving a common goal of coming up with the required contingency analysis in electric power network.
To plan and operate the different stages of a power network is impossible without mastering security analysis. The necessity and importance of a continuous electric power supply stresses the importance and relevance of the study of power system security in real-time situations. To help the operator control and monitor the security of the electric power system requires the development of a set of security analysis functions. These functions involve assessing the security level of the variables obtained from outage studies and control to raise the security level of the system. The ability of the system to reach a state within a specified secure domain following a contingency impact on the system operation is the focus of a steady-state security analysis . The main concerns in security assessment are the efficient and timely identification of the set of critical or potential critical contingencies and their evaluation related to the severity level . Various large-scale software packages such as the PowerWorld program are extensively used . To accomplish this goal, PBL will be used as a way to increase the process of student learning in project assignments on power system analysis. PBL can be used successfully to help students deal with the complexity of an electric power network.
The software package PowerWorld 11.0 was used in order to attain the objectives of this project . Among other things, it provides the simulation of a power flow and security analysis in Electrical Power Systems. In a first stage, a Tests Power Network with 6 busbar was used followed by a second stage where a wider dimension network was applied. The "bounding method"would require the use of the contingency analysis methods, in which case the network would have used the 6 busbar Test Power Network.
The project required specific research work on the Study and Analysis of Security in Electric Power Systems; Security Studies in the Portuguese Electric Power Network; Comparison of the criteria used by European and American organisations and also on Severity indices. Further extensive research work was needed to study the analysis of the n-1 security criterion for a specific load level using the contingency analysis of the PowerWorld 11.0 computing programs package.
To evaluate the impact of overloads in the transmissions' lines and transformers, and the generator units as well as the violation of tension limits in the busbars of the system it was necessary to classify and rank the contingencies using the severity indices. In this study two different sets of security indices were used. The power and the voltage severity indices were used in the first set. The power severity indices were applied to evaluate the overload impact in the network devices. The voltage performance severity indices typify emergency operating conditions where voltage limit violations may occur. The security performance indices of the second set are based on the power losses [8-12]. The screening and ranking of the contingencies is constructed from composites indices obtained through the severity indices and can be obtained in two different ways, estimating the average or weighting the individual indicesÂ , . Finally, some conclusions were presented that provided a valuable contribution to the understanding of the electric power system security analysis. The use of the sets of severity indices produced the changes in the ranking and classification of the contingencies as the methodology allows the easy measurement of control in the security range of an electrical power system.
The same assignment was given to all teams. The materials were divided into four topics so that each student got part of the information needed to complete the proposed task.
At the beginning of the semester, students were divided into groups of four. Each team had specific tasks to perform and records to complete. The assessment of the whole group project depended on the preparation and presentation of a final report.
Each team member was assigned a different role and was given different resources. The suggestions were: a Coordinator. He/she had to subdivide the tasks, assign responsibilities, maintain the pace of the work and check the good quality of the performance. The Coordinator also had to produce a short report explaining how the work was divided and the criteria used to assign them to the different team members. This way each student could concentrate on a part of the material without worrying about having to understand the rest of the material. Each team has three students, with special tasks in the team: the Checker, the Recorder and the Sceptic. The Checker had to monitor not only the solution but also its understanding by the whole team. Although each student is given only a part of the work, he/she will be evaluated on the whole subject. The Recorder, he/she had to check if there was consensus and had to write the team's final version. The Sceptic provided alternative suggestions keeping the team from jumping to premature solutions .
The assignment of different topics, roles and different resources to each member of the teams aims at fostering an interdependency necessary to carry out their final project. Face-to-face interaction is rather important in this type of work. They have to rely on the others and create their own sense of responsibility to study his/her part of the topic that will later on help to compose the final project. As the final evaluation will be on the whole subject, there must be a constant feedback of information to update all the team members on the whole subject matter.
Along the project, students meet with their teachers to be provided with the necessary details for the performance of the task. These meetings intend to guide the groups towards a solution by introducing them to further specific information they will need in order to reach a solution. At the same time, the meetings serve as progress checks, as the teacher will meet with each team coordinator.
The project aims at developing the students' individual responsibility in their learning process; measuring their performance along the project, making them reflect upon and review the whole project and also making them aware of the development of their individual learning skills.
Their final report will be based on their own observation process rather than the mere shallow description of a process devoid of full personal involvement. Students receive significant feedback on their progress.
Also, a student from each team was selected at random by the teachers to present orally the whole team's process - from the methodology to the final product. The team's evaluation was given to all its members based on this performance. This random selection was used to foster individual responsibility as well as the group's involvement in parting information throughout the entire process .
PBL is considered a good way of preparing students for engineering and technology programs.
To evaluate the students' satisfaction and benefits of this process, they were required to answer two questions anonymously:-1."Did you enjoy working in a team project in this particular course?" And 2. "In what way was team project beneficial in developing a research work project?"
The survey referred to the degree of satisfaction using the team work project and the benefits of team project in developing a research work project. The answers were rated from 0 to 5 points scale with 0 indicating poor and 5 representing excellent . As we can see in Fig. 1 a great majority of the students enjoyed working with this kind of methodology of group work. 75% of the students agreed with it.
Fig. 1. 'Did you enjoy working in a team project in this particular course?'
Fig. 2 shows that most of the students felt that the team project helped them to learn better how to perform a research work project. 69% of the students agreed with the method.
Fig. 2. 'in what way was team project beneficial in developing a research work project?'
In addition, as we can see in Fig. 3, there has been a general improvement. The classification system uses a 20 point grading scale wherein 20 is the highest grade and 0 is the lowest. It is required to have at least 10 points to be approved in the course. If we look at the percentages between the scholar years of 2003/04 and 2006/07, it is noticeable that the final grades have become more evenly distributed. In 2003/04 the peak was 75% of students in the range 10-12. In 2006/07 only 44% were included in the same range. If we look at the intermediate range 13-15, it is also noticeable that the grades have considerably risen to 50% in 2006/07.
Figure 3. Final grades for different classes, in different years. Horizontal axis: scale of results of student evaluations
The problem statement is presented to the students. Each assigned team must evaluate and discuss the problem and list its significant parts. Then, possible solutions must be put forward. They have to assess what they need to know to solve the problem; do research and collect data to support their proposed solution. Each team has to assign tasks and set deadlines for each given task. Their report should include all the stages they went through - from the problem statement, the questions, the collected data and proper analysis, the support for the solution or possible recommendations based on the data analysis. The groups of students who used this approach scored higher on the Electric Power System Analysis than students in traditional courses.
The software package PowerWorld 11.0 was necessary to allow the simulation of Power flow in electrical networks. The study of power severity indices were also required to evaluate the overload impact in the network devices. Knowledge of contingency analysis methods was required to implement the project.
PBL and cooperative learning improved the classroom environment. Students learned to master the comparison and analysis processes in order to understand the electric power system security problem. On the other hand, it was noticeable that personal involvement and extremely positive interaction were made possible while working in a responsible way developing the so required skills for the real world.
PBL with students working in groups on real problems generates enthusiasm. This approach benefits the motivation to learn and the students' self-esteem. Students see the potential of the method. PBL addresses many of the concerns of teachers and professional organizations. Above all, it encourages students to be in charge of their education. It emphasizes critical thinking skills, understanding, learning how to learn, and working cooperatively with others.
This project, developed over one semester, has proved to be both enjoyable and challenging for all the parts involved. However, it must be acknowledged that it requires a greater amount of resources, human and otherwise, when compared to the traditional approach.
The benefits of PBL in the Electrical Power Systems course are seen in the way students improved the study and analysis of the security in an electrical power system. This method can also be seen as a benefit for Electric Power Systems where educators strive for improved teaching and learning.