مقاله تأثیر بارهای غیر خطی بر سیستم نیرو و تجهیزات

مقاله تأثیر بارهای غیر خطی بر سیستم نیرو و تجهیزات

مقاله تأثیر بارهای غیر خطی بر سیستم نیرو و تجهیزات

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مقاله تأثیر بارهای غیر خطی بر سیستم نیرو و تجهیزات

Impact of Nonlinear Loads on Power System and Equipment

۱۶٫۱ Introduction

Harmonics are a convenient way of expressing the waveform distortion caused by nonlinear loads in electrical power systems. Before the introduction of power electronics, most nonlinear loads were the result of static rectifier systems or the operation of transformers of shunt reactors at voltages beyond their magnetizing knee
point, i.e., beyond their linear region.

Since the introduction of power electronics into industrial systems, waveform distortion has become more common, and the need for analysis of the resultant harmonics has increased. Other waveform distortions occur when transformers are energized, but these harmonics are transient in nature. Harmonics can also cause resonance with, and overloading of, devices designed to operate at fundamental frequencies only.

To control the level of harmonics in any system, it is important to know both the source of harmonics and the devices that are sensitive to such harmonics to limit their effect in any network.

۱۶٫۲ Harmonics and Resonance

۱۶٫۲٫۱ What Are Harmonics?

Harmonics are voltages or currents in the electrical system at some multiple of fundamental frequency (60 Hz in North America).

Any periodic wave can be described mathematically as a sum of sinusoidal wave forms in a Fourier series, named after the French mathematician Jean Fourier (۱۷۶۸–۱۸۳۰). The frequency of each sinusoid is an integer multiple of the frequency represented by the fundamental periodic cycle or frequency. Each term in the series is referred to as a harmonic of the fundamental frequency. A square wave, as shown in fig. 16.1 (common for a full-wave static rectifier), is the sum of an infinite series of odd harmonic sinusoidal wave forms. This can be expressed as follows