What are the Causes/Reasons for 15th Harmonic Occurrence

http://www.hersheyenergy.com/harmonics.html

Are you saying that the 15th harmonic is stronger than any other harmonic on the phase...even the third?

There is a mathematical relationship between the 3rd and 5th harmonics and their related multiples.

Is it possible for you to post an image from your test equipment?

Found this might help...

http://www.allaboutcircuits.com/vol_2/chpt_10/7.html

If this 15th harmonic is large, and is dominant over the other harmonics, I would be concerned. Are you measuring this on the voltage or the current? What amplitude are you measuring?

There isn't any reason for it to be produced by UPS, CFL.. as 750Hz is a lower frequency than what most switching topology use. Instability and sub harmonics could be present but this is a far shot.

It could be something special such a an induction heating furnance or an ozone generator... In this case, it is likely that the frequency would vary with the load.

Fortunately, at this frequency, a "simple" LRC circuit can be used to filter it out. There shouldn't be so much energy to absorb.

The load is not specific as I am taking sample on distribution box of an commercial complex where mix of all AC UPS LIFTS CFL TV and other electronic devices will be present. but 15th harmonic is only present.

Non-linear load is the cause of distortion. As others have pointed out, a square wave will generate all odd harmonics, and anything short of a perfect square wave will produce some evens as well. A varying duty ratio can cause many different harmonics to prevail.

You could temporarily replace the load with a pure resistor to test for this. The result should be a pretty good sine wave.

In any case, filtering is the fast and easy solution.

http://www.electriciansforums.co.uk/electrical-forum-general-electrical-forum/2299-problems-caused-voltage-optimisers.html

http://www.powerswitch.org.uk/forum/viewtopic.php?t=17893&postdays=0&postorder=asc&start=0

15th ??????????

Not known before higher than 7th which is not in gen sets but in Inverters using quosi-sine protocols.

Sir,

You have recognized a problem that will continue to increase in its severity and cost in the coming years. The cause is "non-linear" loads--loads in which the current and voltage waveforms do not have the same shape (they have a non-linear mathematical relationship between them at different points along the sine-wave curve of the voltage waveform). Fourier transform analysis of the current waveform recreates this waveform as a sum of many sine waves, each one being a multiple of the base frequency, but each one with a different amplitude. For wye-connected 3-phase loads, with non-linear loads on all three legs, most harmonics will cancel out through the neutral, so the neutral and the transformer(s) upstream see only the difference between them. However, the odd multiples of the third harmonic are additive (they do not cancel).

I have seen a variable frequency drive installation in which the harmonics on the power line were significant even up past the 40th, and the total harmonic distortion was in excess of 200%. There are many good resources available from manufacturers and on-line, that will explain the phenomenon and its problems/causes much better than I have here.

Almost every device that begins by converting the incoming AC to DC is a non-linear load, and will therefore be a source of the harmonics you have mentioned. This will include electronic lighting ballasts, computer power supplies, UPS's, VFD's, etc., etc., etc.

There are a number of methods which you can use to handle this problem. They include:

1. Ignore them (but they won't go away, and problems will get worse).
2. Ferro-resonant transformers (they are very effective in absorbing them, but $$).
3. Low-pass L-C filters (but beware of higher voltages if the filter remains on line when the load is reduced).
4. Use of "K-factor" power transformers upstream (they are designed to partially absorb the harmonics, but have more heat loss and higher initial cost; on the other side, the % harmonics will require significant derating of an ordinary transformer, so...).
5. Requiring the use of equipment that has very low power-line harmonic distortion (it will use active devices or passive filters internally to do this).
6. Some active devices are beginning to come into the market place (I lack knowledge regarding them).

Hope this helps--JMM