Harmonic Filters Overview - Part One

Published: 8 Apr 2003
By Samprita Thota, Research Analyst
Whatever is a harmonic filter? What are harmonics? What does it mean to have harmonics in my system? Why do I need to filter harmonics? Are there different types of harmonic filters? This article intends to provide an overview on harmonic filters and hopefully answer some of the questions that you might have on them.
Introduction to Harmonic Filters and Harmonics
A harmonic filter is used to eliminate the harmonic distortion caused by appliances. Harmonics are currents and voltages that are continuous multiples of the fundamental frequency of 60 Hz such as 120 Hz (2nd harmonic) and 300 Hz (5th harmonic). Harmonic currents provide power that cannot be used and also takes up electrical system capacity. Large quantities of harmonics can lead to malfunctioning of the system that results in downtime and increase in operating costs. The second harmonic would have a frequency of 120 Hz; the third harmonic would have a frequency of 180 Hz and so on.
Inside the Harmonic Filter
The harmonic filter is built using an array of capacitors, inductors, and resistors that deflect harmonic currents to the ground. Each harmonic filter could contain many such elements, each of which is used to deflect harmonics of a specific frequency.
The Cause and the Effect
Harmonic distortion is caused by equipment that are non-linear loads. These loads use current in a pulsing manner and at times feed harmonic currents back into the wiring. In non-linear loads, the current waveform is different from the applied voltage waveform. This causes them to produce the following:

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