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Session 2333

Development of a Laboratory Experiment to Demonstrate Power Quality Issues

Timothy L. Skvarenina Purdue University

ABSTRACT

Less than 15 years ago, harmonics were not even mentioned in an articlel listing all of the problems with electrical power that could cause malfl.mctions or damage to electronic equipment. However, the widespread application of electronic devices in business and industry is causing new problems for power systems. Nonlinear loads, such as the power supplies for electronic devices, introduce harmonic currents into the power system, which can cause failures in power system equipment as well as in other loads. Evidence of harmonic problems include circuit breakers tripping when they shouldn’t or failing to trip when they should, overheated neutral conductors or transformers, erratic operation or tripping of adjustable speed drives, blown power factor correction capacitors, and communication interference. The problems are different, but their causes are related.

Since every user of the power system contributes to the problem, I believe all electrical engineers and technicians need to have a basic understanding of power quality issues. All undergraduates in the EET curriculum at Purdue are being provided with such a background in the form of lecture material and hands-on laboratory experience. Because of budget constraints, emphasis was placed on developing an experiment that could be performed with inexpensive loads and use equipment that is available in most electronics and power laboratories (e.g., oscilloscope, true-RMS voltmeter). During the development of the experiment, our department was fortunate enough to receive a gifi from the Fluke Corporation of Power Harmonic Analysis Meters, which greatly enhanced the students’ laboratory experience.

This paper discusses some of the basic theory of harmonics and their effects on the power system, followed by a description of the laboratory experiment.

INTRODUCTION What are harmonics?

The voltage waveform received from the power company normally consists of a single frequency sinusoid. For linear loads on the power system (resistors, inductors, and capacitors) the current will also be a single frequency sinusoid. However, some loads are nonlinear loads and cause a nonsinusoidal current when a sinusoidal voltage is applied. Nonlinear loads often contain some type of switching device that causes noncontinuous operation. Examples include the power supplies for electronic devices including computers, programmable controllers, and oflice equipment; variable frequency motor drives; and electronic ballasts for fluorescent lights. Although the current is not sinusoidal for a nonlinear load, it is periodic, assuming the load is in a steady-state operating condition.

{tixi$~ 1996 ASEE Annual Conference Proceedings ‘@lly’:

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Skvarenina, T. L. (1996, June), Development Of A Laboratory Experiment To Demonstrate Power Quality Issues Paper presented at 1996 Annual Conference, Washington, District of Columbia. 10.18260/1-2--5983