Triple Harmonics

Sparky Joe

Can anyone explain to me how triplens work, how they are created and why they can put more current on the neutral? doesn't this go against Kirchoff's law?

I think I have a good idea; on multiwire circuits where only the imbalance is handled by the neutral, when you get a triple harmonic: the third phase(in refferrence to the first) is actually on the same cycle as the triplen, though it cannot balance it because it itself hasn't 'pushed' as much current as it is trying to recieve.

Am I on the right track? Or is my own explanation too difficult to understand?

CE1

Try this:

Harmonics are voltages or currents at frequencies that are a multiple of the fundamental frequency. In most systems, the fundamental frequency is 60 Hz. Therefore; harmonic order is 120 Hz, 180 Hz, 240 Hz and so on. If the fundamental power frequency is 60 Hz, then the 2nd harmonic is 120 Hz, the 3rd is 180 Hz, etc. When harmonic frequencies are prevalent, electrical power panels and transformers become mechanically resonant to the magnetic fields generated by higher frequency harmonics. When this happens, the power panel or transformer vibrates and emits a buzzing sound for the different harmonic frequencies. Harmonics are caused by and are the by-product of modern electronic equipment such as personal or notebook computers, laser printers, fax machines, telephone systems, stereos, radios, TVs, adjustable speed drives and variable frequency drives, battery chargers, UPS, and any other equipment powered by switched-mode power supply equipment.
In an electrical distribution system harmonics create large load currents in the neutral wires of a 3-phase system. Theoretically the neutral current can be up to the sum of all 3 phases therefore causing overheating of the neutral wires. Since only the phase wires are protected by circuit breakers of fuses, this can result in a potential fire hazard.
Do you know how to use an oscilloscope? An oscilloscope is a good tool to have and with one you could actually see the different harmonics.

Here is what my portable oscilloscope looks like on a 120 VAC outlet. The scope shows about 330 volts peak to peak. If you look real close you might see the noise and some harmonics in the sine wave. The fuzzyness of the sine wave is noise and the harmonics are right at the peak or valley of the sine wave.


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mdshunk

Remember that many of your electronic devices act much like putting a big capacitor or inductor on the line, effectively "moving" the waveform "returning" on the neutral out of phase with the normal waveform. We refer to this as "leading" or "lagging". This is the beginnings of harmonic troubles.

Sparky Joe

Great post CE1 very informative. Your talking about power factor MD with E and I out of phase? Like CE1 said with, electronic switching devices, when the switch hits a frequency that is say 180Hz you get a triple harmonic. Those spikes at the peaks on your scope are transients aren't they? Like when someone turns on a huge motor load in your neighborhood you'll get a spike on your line hitting around 500 volts and always at a peak of the wave, thus burning up the elctronics in your house which is why we install TVSS's?
BTW how much was your scope and how portable is it, I've seen some from Fluke around 1600 bucks.
And what was your bottom graph showing?

ATS

The American Electricians Handbook has some real good information on harmonics, the cause and mitigation, good reading! My advice, don't worry about it, just carry 2 ammeters, a true rms and an averaging. If you're having a problem relating to harmonics on the line you will have a difference between the 2 meter readings. You'll need to to do a ton of service calls to pay for that scope. There are harmonic filters and shunts that can be installed as well if need be.

Sparky Joe

Thanks ATS

CE1

No there were no spikes in the graphs, just noise and some harmonics. The bottom graph is showing a zoom window of the first graph. The meter costs about $400.00 and is made by EXTECH instruments. It is a little larger than a standard multimeter and I can very easily hold it in one hand. Fluke is overpriced and you are just paying extra for the name.

Meter information:
http://www.extech.com/instrument/pro...99/381285.html

Extended reading on power problems:
http://www.apcmedia.com/salestools/V...KLPK_R0_EN.pdf

There will be a test on this next week.