Power system harmonics are integer multiples of the fundamental power system frequency created by non-linear devices connected to the power system. High levels of power system harmonics can create voltage distortion and power quality problems. Harmonics in power systems result in increased heating in the equipment and conductors, misfiring in variable speed drives, and torque pulsations in motors.

1. The Effect of Harmonics on Electric Metering

Power system harmonics distort the shape of the perfect voltage and current sinusoidal waveforms ideal to the power grid, and are multiples of the fundamental grid frequencies of 50 or 60 hertz found throughout the world. Problems caused by harmonics include overloaded circuits and higher system losses that can lead to premature equipment failure in utility and customer systems. Low utility power factor is generally associated with harmonics in electric metering.

Read more on this link http://www.ehow.com/about_6676198_effect-harmonics-electric-metering.html

2. Power System Harmonics Causes and Effects of Variable Frequency Drives Relative to the IEEE 519-1992 Standard

This document describes power system harmonics as they relate to AC variable frequency drives controlling centrifugal pumping applications. Some of the topics covered are:
o Definition of harmonics
o How AC variable frequency drives create harmonics
o Effects of variable frequency drives on the AC line
o Three-phase harmonics associated with phase-to-phase loads
o Controlling harmonics
o Information on the IEEE 519-1992 standard, “IEEE Recommended Practices
and Requirements for Harmonic Control in Electrical Power Systems”

Read more on this link http://www.alamedaelectric.com/Modicon%20Documents/AC%20Drive%20Power%20System%20Harmonics.pdf

3. POWER SYSTEM HARMONICS - A Reference Guide to Causes, Effects and Corrective Measures

This paper is intended to give an overview of power system harmonics and is aimed at those who have some electrical background but little or no knowledge of harmonics. The basics of harmonics including Fourier
theory are explained briefly.  Common types of harmonic sources present in industry are addressed with particular emphasis on variable frequency drives.

 The potential ill-effects due to harmonics are detailed. The recommendations of IEEE Std. 519-1992 are dealt with. A proactive approach for the addition of large non-linear loads is then presented and alternative methods for harmonic reduction are discussed.

Read more and free ebook download on this link http://samplecode.rockwellautomation.com/idc/groups/literature/documents/wp/mvb-wp011_-en-p.pdf


The objective of the electric utility is to deliver sinusoidal voltage at fairly constant magnitude throughout their system.  This objective is complicated by the fact that there are loads on the system that produce harmonic currents.  These currents result in distorted voltages and currents that can adversely impact the system
performance in different ways.

As the number of harmonic producing loads has increased over the years, it has become increasingly necessary to address their influence when making any additions or changes to an Installation.

Read more and free ebook download on this link  http://www.powerstudies.com/articles/Harm_Intro.pdf

5. Harmonics in polyphase power systems
In the chapter on mixed-frequency signals, we explored the concept of harmonics in AC systems: frequencies that are integer multiples of the fundamental source frequency. With AC power systems where the source voltage waveform coming from an AC generator (alternator) is supposed to be a single-frequency sine wave, undistorted, there should be no harmonic content . . . ideally.

Read more and free ebook download on this link  http://www.allaboutcircuits.com/pdf/AC.pdf

6. Tracking interference from power-system harmonics

Over the last few years, operation of the power system has undergone a dramatic change, driven by two factors: the increasing need for energy conservation and the emergence of low-cost power semiconductors. The combination of these forces has resulted in a large number of nonlinear loads being connected to the power system. These loads generate distorted currents, which contain higher-than-normal frequencies called harmonics. These harmonic currents, in turn, generate stray magnetic fields and ground loops--what we don`t want near our cabling system.

If you are going to successfully troubleshoot interference from power-system harmonics, you`ll need to understand some basics, including how harmonics are generated and how they flow around the power system. Next, you`ll need a systematic approach to finding the source of interference. And finally, some ideas for potential solutions will be helpful.

Read more on this link http://www.cablinginstall.com/index/display/article-display/62690/articles/cabling-installation-maintenance/volume-4/issue-9/contents/special-report/tracking-interference-from-power-system-harmonics.html

7. Power System Harmonics in Commercial and Industrial Applications

For many Power System designers, understanding the load requirement is only the first step. As equipment complexity increases, so does the diversity of use. One aspect seems to remain constant; the growth of non-linear loads due to DC equipment such as computers, fax machines, uninterruptible power supplies
(UPS’s), monitors and displays, fluorescent lighting, and many other devices that switch on and off rapidly such as  variable frequency drives (VFD’s) for motors. The result of the introduction of such equipment is the proliferation of “harmonic pollution”.

Read more on this link http://www.fire-cables.co.uk/documents/Power%20System%20Harmonics.pdf

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