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Session 1532

Teaching Three-Phase Electrical Power Using a Low-Voltage Power Source

Thad B. Welch, John N. Berry United States Naval Academy/United States Air Force Academy

Abstract

The United States Air Force Academy teaches a first course in Electrical Power Systems. While computer simulations and modeling techniques have become pervasive throughout most of the engineering curricula, and while the utilization of computers in the classroom and the laboratory represents a major pedagogical improvement, a hardware-based approach to teaching several electrical power distribution and usage topics can also be very effective. Our course includes several laboratory experiments and demonstrations designed to involve the student in the learning process. A locally designed and manufactured three-phase, low-voltage, variable- frequency power supply is used to teach parts of this Electrical Power Systems course. The three- phase low-voltage system enhances student safety while allowing for student involvement in the learning process. Additional laboratory time also leads to numerous other learning opportunities for the student. This paper discusses the utilization of the three-phase low-voltage power supply as a teaching tool. A discussion of several laboratory experiments and demonstrations is included. Some of these demonstrations, for example, slowing the power supply frequency to the point that phase rotation is visible without the use of electronic test equipment, cannot be accomplished using the more traditional high voltage “power bench” type equipment. Finally, the limitations of the three-phase low-voltage power supply are discussed.

I. INTRODUCTION

Electrical power systems are an essential part of the world’s infrastructure, economy, and way of life. Indeed, without a reliable source of power, many of the daily activities in a large part of the world would not be possible. The vast majority of the electrical power in the world is generated and distributed via three-phase power systems [1]. The basic concepts of three-phase power are taught to a wide variety of engineers in either a general circuits course or a class dedicated to energy conversion and power systems.

The systems used as examples when teaching power systems typically involve dangerously high voltages and currents. For obvious reasons of safety and logistics, it is not practical to have students work with actual power systems. Power demonstration stations that allow students to work with relatively low voltages (hundreds of volts) in a laboratory setting are available. With these stations, students can build and experiment with motors and other three-phase loads. However, these demonstration stations are usually large (the size of a lab bench), expensive (typically tens of thousands of dollars), potentially dangerous, and require that three-phase power be available in the laboratory. With a small, low-voltage (several volts), three-phase voltage source, powered by a DC supply, students can safely perform a wide variety of experiments involving three-phase power systems. In addition, the supply could be used as a portable demonstration unit, helping students visualize basic three-phase concepts in the classroom.

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Berry, J. N., & Welch, T. (1998, June), Teaching Three Phase Electrical Power Using A Low Voltage Power Source Paper presented at 1998 Annual Conference, Seattle, Washington. 10.18260/1-2--7459