Electric machine undergraduate lab: a traditional approach with a new technical base

International Journal of Electrical Engineering Education, Jan 2007 by Conejo, A J, Arroyo, J M, Milano, F, Mora, J A

Abstract We describe our experience of designing and building an electrical machine laboratory and using it for undergraduate teaching. Using small, well-balanced machines, we pursue a design that allows the closest possible man-machine contact, so that students develop a direct understanding of the machine. We summarise our practical teaching experience and lessons learned.

Keywords electric machines; transformers; undergraduate laboratory

This paper describes our experience of designing and building an undergraduate electrical machine laboratory, and using it for practical teaching throughout the last decade. This laboratory is used for practical teaching in the Department of Electrical Engineering of the University of Castilla-La Mancha, in Ciudad Real, Spain. It is embedded in a one-semester course on electrical machines, which is usually taken by students during the third year of their five-year electrical engineering degree.

Students taking this laboratory have appropriate theoretical background on circuit theory1,2 and single-phase transformers as well as three-phase transformers and rotating machines.3,4

We believe that practical teaching through appropriate laboratory work is essential to the power engineering profession and this paper is intended to revitalise such teaching.

At a time of dismantling electric machine laboratories in distinguished power engineering institutions throughout the world, we believe that our experience might help others to restructure instead of suppressing electric machine laboratories. Indeed, this is one main reason for writing this paper.

As opposed to what is common practice in many well-known institutions, we use small, well-balanced machines of capacity below 1 kVA. This approach results in low cost and high flexibility to arrange different tests. In addition, the practical relevance of the laboratory experience is not limited, and hands-on experience is facilitated. And, more importantly, the laboratory is safer for students, particularly the na�ve ones.

While cheap control equipment and sophisticated computer simulation systems are widespread nowadays, in our laboratory we emphasise man-machine proximity, eliminating as many control systems as possible, so that the student can 'feel' the machine and learn its behaviour. In other words, no commercial self-contained workstations, which are inflexible and costly, are used. Instead, the students are required to manually wire the various implementations and physically couple the machines involved in each experiment. We believe this is an important learning experience.

Furthermore, empirical results are assessed through computational simulation, which is not intended to eliminate hands-on experience.

Our experience shows that through this laboratory students become motivated to understand electrical machine performance and, in general, become highly interested in power engineering.

We also provide students with adequate practical knowledge of electrical machines which is of clear interest in their future professional activities.

This paper positions itself in the educational literature pertaining to the practical teaching of electric machines, which includes, among others, the relevant publications Refs 5-13. Within the classification framework stated in Ref. 7, we describe an electric machine laboratory that (i) is machine oriented, (ii) does not rely on workstations, (iii) promotes man-machine proximity, and (iv) avoids control systems that make it difficult for students to understand machine behaviour. This laboratory complements the integrated setting recently presented in Ref. 13, by focusing on electric machines and on the necessary man-machine proximity for efficacious laboratory work. Naturally, we also emphasise safety.

The rest of this paper is organised as follows. The next section describes the physical setting and the equipment available in the laboratory of electrical machines at the University of Castilla-La Mancha, in Ciudad Real, Spain. A description of part of the laboratory work carried out by the students follows. Then, the educational experience and the lessons learned from decade-long practical teaching are summarised. Finally, some relevant conclusions are presented.

Physical setting

The metering instrumentation as well as the laboratory physical plant and organisation are presented to students in the first session. The physical plant of the laboratory is designed so that students have sufficient space to arrange tests by themselves. The electric machine laboratory is equipped with:

* 1kVA, 380/127V, 50 Hz three-phase transformers (Fig. 1);

* 0.4kVA, 400/230V, 1.16/2A, 1340r/min, 50 Hz three-phase induction machines;

* 0.3kVA, 400/230V, 0.66/1.14 A, 1500 r/min, 50 Hz three-phase synchronous machines (Fig. 2);

* 0.25kW, 220V, 1.4 A, 2000 r/min, d.c. machines, which are used as prime movers for the synchronous machines (Fig. 3);

* 3kVA, 380/430V, 50Hz three-phase autotransformers to supply variable a.c. power to the transformers and induction machines from the 380V three-phase grid (Fig. 4);