Sources of Harmonics

with true sine waves you have minimal hamonics.

With switchers that use square waves the math of square waves means they are made up of an infinite summ of all odd order harmonics of the fundamental wave.

http://www.google.ca/search?hl=en&safe=off&q=%22square+wave%22+%2B%22odd+order%22+%2Bharmonics&btnG=Search

the makers of these attenuate with some rounded edge switching and low pass filtering to limit the wire carried harmonics. sadly, you can find noise all the way up 500 MHZ in the inputs of sensitive receives, so in uses where this is a problem, some sort of faraday shield is needed.

VFD's can raise all sorts of hell (harmonics -wise ) on a system ... this would also include a lot of spindle drives from machine tools,(especially older machines) cranes ,etc the harmonics they create can overheat conductors and switchgear and create all sorts of problems

I had an 18th harmonic once caused by the pitch wind of a generator, so the experts told me. 5/6 pitch created harmonics and a 2/3 pitch solved it. Don't know if I belived it or not after all the equations on the board were done and I'm too dumb to disagree. If your power source is a local generator then check into the pitch wind.

The comment about VFDs is all too true as well. If you have VFDs and the power is a local generator I can FOR SURE tell you that the voltage regulator of the generator gets fooled. I have many tricks to solve this if it is so. Write back!

George

There is another thread on the same topic:

The Role of Harmonics in Transformers <http://globalspec.ip09.com/rd/9z1zh0io8jcbnrrdat3lp50p4v8lkqjvgamr4o7512o>

(Electrical Engineering)

posted by Guest on Sunday Jan 28, @08:32

can any one give me the clear idea about the harmonics and the role of harmonics in transformers and how they can be nullified?

The simple (but not the simpler – according to Mr. Einstein) three sources of harmonics are:

1. Power grid (with its generators) voltage
2. Non-linear loads
3. Specific switches (e.g. with triacs)

Some harmonics could have the resonance frequencies of the electronic circuits (mostly with L & C elements).

These circuits that have an electronic semiconductor should create a glitch of resonance's high voltage that will kill it.

Three common sources of harmonics in a commercial/industrial environment are:

VFDs

High frequency electronic ballasts (fluorescent lights).

Switched mode power supplies found in computers and other electronic devices.

These harmonics can affect other sensitive devices and can also cause a cumulative neutral load since the harmonics do not cancel out on the neutral but instead add together.

Modern engineering design takes this into account and oversized neutrals are not uncommon. Also, the some of the newest VFDs hitting the market right now are somewhat harmonic cancelling.

Steve Gardner
Engineer
Test Point Inc.
www.testpoint.com

Good examples of load + switches that create harmonics because of their non-linear characteristics!

These "inject" current harmonics into the grid and they create harmonics in supplied voltage that next enter even pretty linear loads connected to the grid. In the residential electronics there are possible demages.

Of course much higher risk is from inducted waves coming from lighning around overhead lines. So unplug them when you hear/see lightninh because there is no 100% surge protection!

In neutral wires added are odd harmonics e.g. 3-rd that are in USA 3*60 = 180 Hz or 150 Hz in EU.