If you have an FFT function, you can see the harmonic content of that sine wave.

Below is a panoramic view of the 60 Hz at my shop when I was in western Oklahoma, about 125 miles N of Amarillo TX. The generating plant was in Amarillo.

FYI: In case you use this figure for anything that matters, you've got a couple of labels that have the attenuation in Hz instead of dB.

 

It's called panoramic because I put together a lot of screen shots for the overall picture. I just identified the level and the frequency on the picture because I cropped the left hand edge where the amplitude scale was located on the successive screen shots.

I don't know if the same conditions exist or not as I never repeated the measurement before I left western Oklahoma.

 

I think you make a pretty good case for utility power being far from clean and perfect!

 

It's called panoramic because I put together a lot of screen shots for the overall picture. I just identified the level and the frequency on the picture because I cropped the left hand edge where the amplitude scale was located on the successive screen shots.

I don't know if the same conditions exist or not as I never repeated the measurement before I left western Oklahoma.

Here's what I'm referring to:

 

Thank you WBahn ... I'll see if I can edit that ... you are the master of details, and I usually catch small errors of that nature.

 

I think you make a pretty good case for utility power being far from clean and perfect!

What would you consider "clean"? I don't think anyone is saying that the grid power is perfect. But notice that the worst harmonic (the 3rd) is still down 35dB, meaning that the power in that harmonic is less than 1/3000th that of the fundamental. On a 120VAC line, that means that it's amplitude is only about 2V. Most of the harmonics are in the -50+dB range, which places their amplitudes in the quarter volt range. That seems fairly clean. In fact, a conservative estimate would indicate that 99.9% of the power is in the fundamental.

Also, notice that all of the harmonics are below the -30dB DC level that was measured, which is about 4V. Even taking that into account, there is still over 98% of the power in the fundamental.

 

Thank you WBahn ... I'll see if I can edit that ... you are the master of details, and I usually catch small errors of that nature.

I'm always catching minor details like that -- in someone else's work. I get really frustrated by how often I miss those kinds of errors in my own, even after several proofreadings. I understand the mechanism involved, namely that our mind tends to see what we intended to write rather than what we actually wrote, but that makes it no less aggravating.

 

@WBahn...That's why a community is good. We catch each other's mistakes.

@tcm...Now, now. I'm a pragmatist, too, but we can't demand that everybody else quit chasing nits. Even if it's useless for practical matters, it's educational. Post#26 was educational for me. Putting distortion in terms of db down hits one of my math abilities.

 

@tcm...Now, now. I'm a pragmatist, too, but we can't demand that everybody else quit chasing nits. Even if it's useless for practical matters, it's educational. Post#26 was educational for me. Putting distortion in terms of db down hits one of my math abilities.

I find it rather to my point. At what level do you consider something good enough and is that level a rational one or unrealistic and obsessive one and who decides?

Personally I never cared fore the dB system. I prefer fractions and percentages.

 

I find it rather to my point. At what level do you consider something good enough and is that level a rational one or unrealistic and obsessive one and who decides?

Personally I never cared fore the dB system. I prefer fractions and percentages.

TCMTech,

I am interested to hear what your calibrated eye and the rules on your thumb might deem to be an unacceptable waveform from a Genset. At some point, a waveform has to have too much THD to be acceptable for use on inductive loads (do you agree?). I would be interested in your take on what is too much and what that too much might look like as a waveform.

 

When testing a generator set, I always tested them at maximum load. I did have a four step load on my 300 kW generators. When I first tested them, I noticed the line currents were not balanced and I spent a few days going over each leg of the loads finding lots of fuses blown as the cause of the problem.

What upset me the most was the contracting officer's technical representative had already accepted the installation.

I've tested 1 kW generators loaded with a string of incandescent lamps ... but I never viewed the signal other than for voltage levels and maybe frequency ... never with an oscilloscope.

I created that panoramic because my former unit had complained about a distorted AC power waveforms. It turned out that the cause of the distortion was the line filters designed to keep out that 800kW 100 kHz signal from the equipment room.

Using the first sixteen readings, the THD is about 1.98%. I had sent that to the engineers who was addressing the problem as a clue the incoming power was clean at my location ... which was about 30 miles from the unit.

You won't know if the generator will perform under full load unless you test it under full load.

The voltages are indicated on one graph and the dB on the other. The additional pic was the simulation within good agreement of the calculations.

I keep remembering the comments of J.A. Pierce, who chose 10.2 kHz as the frequency for Omega ... he stated something to the effect that he should have thought it out better as 10.2 kHz is the 170th harmonic of 60 Hz ... which caused interference to the Omega signal that they were investigating.

I like the dB scale because it illustrates the signal levels clearly as opposed to the voltage levels.

 

I am interested to hear what your calibrated eye and the rules on your thumb might deem to be an unacceptable waveform from a Genset. At some point, a waveform has to have too much THD to be acceptable for use on inductive loads (do you agree?). I would be interested in your take on what is too much and what that too much might look like as a waveform.

On my books for a portable generator system anything within the standard specs of +- 10% voltage +- 10% frequency less than 10% harmonics distortion/energy level and a power factor above .8 is good.

Harmonics and waveform distortion wise I could care less until they start noticeably affecting other aspects of operation or start interfering with things and that usually means that on a gen set powering a limited number of devices and loads things have to get pretty bad to to show up.

If the devices being powered aren't being negatively affected I don't bother worrying about the power quality.

 

On my books for a portable generator system anything within the standard specs of +- 10% voltage +- 10% frequency less than 10% harmonics distortion/energy level and a power factor above .8 is good.

Harmonics and waveform distortion wise I could care less until they start noticeably affecting other aspects of operation or start interfering with things and that usually means that on a gen set powering a limited number of devices and loads things have to get pretty bad to to show up.

If the devices being powered aren't being negatively affected I don't bother worrying about the power quality.

Tcmtech,

That is my concern with your rresponses to this OP. one minute you say he needs to be medicated because he is worrying about nothing. Now you say distortion above 10% is concerning. Which is it? From my point of view, the waveform shown could very well be 10% or more - my eye is not calibrated but I would not insult or diagnose the OP for being concerned.

Secondly, you say all is good if the downstream equipment does not show ill-effects of the distorted waveform. How do you know that it doesnt?

the whole point of this site is to help people learn and solve problems, not to suggest medication. Or worse yet, to keep recommending medication after they obviously ignored your comments.

I do understand that members sometimes concern themselves with imaginary problems (I.e. "audiophiles"). But, in this case, the problem is in the realistic realm, and the background noise you are creating is not helpful.

 

What I am saying is if the equipment does not have obvious issues with the power quality then I tend to leave it alone.

That said if the power quality is bad enough I consider getting to within a +- 10% of normal to be more than adequate.

Now relating to the reality of how bad power quality can be that again depends on the device.

The way I see it the vast majority of devices can work off of common power inverters that put out nothing better than a square wave which looks nothing at all like a sine wave plus usually has loads of harmonics and the like with it.

As far as how do I know if the waveform the OP has is causing problems well I dont. But then he never said it did. It just didn't look the way he thinks it should with absolutely no reasoning to the need for it being corrected.

What he did say was he was looking at his 15 KW genset power output during some undefined conditions and saw a waveform that does not meet his expectations of what a sine wave should look like.