Abstract:

This paper proposes a systematic method for the diagnostic of circuit failures aimed to improve student proficiency during electrical machine lab activities. The motivation for developing such method has is origin in the experience of the author in teaching electrical machine in the Industrial Engineering course at the University of Castilla-La Mancha for the last eight years. Laboratory activities of the fundamental course on electrical machines consist of five assignments, for which students are requested to manually mount the electrical circuits for testing and measuring transformers and induction machines.

One of the main objects of such laboratory activities is that the students manually mount the circuits. With this aim, the students are provided with a detailed outline of the activity and are taught a simple method to properly mount the circuits and the measurements. Despite the available information, mounting circuit, especially three-phase ones and series measurement instruments, is highly error-prone. This results in long execution times, blowing several fuses and, in some cases, damaging instruments. Wrongly mounted circuits are also cause of frustration and reduce the interest of the students in the lab activity itself.

The main reason for the high rate of issues encountered by the students is that, if the circuit does not work properly, students do not apply any efficient strategy to understand which are the wrong connections and why they are wrong. The typical approach is to try to follow the path and the connections of the cables, which is both very little efficient and almost useless from the learning point of view.

In the last two years, a systematic approach to solve circuit failures has been experimented during lab activities. Students are taught a diagnostic method to define the critical points of the circuit and the countermeasures that can be taken to solve the issue. The diagnostic is based on observation, on additional measures and on the application of circuit theory basic laws. Whenever necessary, simple yet efficacious tests are implemented in order to better understand the problem. In other words, the non-working circuit is considered like a “patient” affected by an unknown “disease”. Similarly to health diseases, most common failures are considered first and adequate measures are taken in order to prove the diagnosis. If this fails, other less common failure causes are considered and other measures are taken, and so on. A detailed list of all mounting errors and resulting circuital failures that can occur in electrical machine lab is provided in the paper.

In order to be effective, this strategy requires a preliminary explanation of the circuit failure kinds and their probability. The concept of probability of a certain issue is new for the students and, thus, is generally perceived with interest. Moreover, students learn how to face real problems and how to solve them in a rational engineer-oriented and systematic manner that deeply involves all their theoretical knowledge. Finally, since the detection of the cause of a certain failure is a kind of parlour game, laboratory activities become a challenging experience.

Keywords:

Electrical machines, laboratory activity, circuit theory, circuit failure.