Transcript
Introduction to 3D Harmonic Graphs
Good afternoon, everyone, and welcome to today’s white paper webinar. Today, we’re here with David Keaton, and we are talking about 3D harmonic graphs. We’re gonna show you how to use these for power quality analysis, and in particular, how this works in PQ Canvas, our cloud-based analysis system, to help you speed up your harmonic analysis.
Analyzing harmonics is a complicated thing with power quality. There are 50 harmonics for voltage and for current, and if you have to go through all of them, it can take quite a bit of time. So we’re gonna show you how to use a 3D graph to speed up that investigation.
Viewing 3D Harmonics in PQ Canvas
So here we have a recording here. This is recording the one through 15th harmonics. All we have to do is click 3D Harmonics up here. We have a choice of voltage or current harmonics. Go ahead and click our voltage harmonics.
And we have an overview of each of the harmonics and their magnitudes, which will give us a nice overview of which ones we need to pay attention to further in strip charts for more granular analysis. So as we can see here, the fifth harmonic is quite high, and the seventh harmonic is as well. So we can go to Interval, go to Voltage Harmonic Magnitude and choose our fifth and seventh harmonics. Can now zoom in and see exactly how much harmonic magnitude we have for those.
Recording With 51 Harmonics
Take a look at another recording here. This one has 51 harmonics enabled, so we can get a much larger overview of all the harmonics and where they sit. So we can see here the fifth harmonic is extremely high compared to the rest of them, as well as the seventh again. You can also move the graph around and rotate it in order to get a better view of where each of them lie.
The key really is that most of the time, the higher order harmonics are near zero, and usually only a handful of harmonics are high, but you don’t know which harmonics those are, and you don’t know if the high ones are zero or not or low unless you look. And as David just showed, you can look at individual harmonics.
So you could pick the harmonics and look at all of them or look at them one at a time, but that’s a very tedious, time-consuming process if you don’t know in advance that some of the harmonics are close to zero and you don’t even need to look at them. If you hear we got 50 harmonics recorded, it would take quite a while to go through all those 50 harmonics and verify that most of them are zero. There’s no point in doing that if a lot of them are very low.
Using the 3D Graph as an Overview Tool
So the 3D graph is really the best way to start. If you have a harmonic analysis, it’s often best to start with a 3D graph. And as David’s showing here, most of the harmonics are zero. So for those that are zero, and we’re showing the entire recording here, you’re done with those. You don’t need to look at them in 2D detail. They’re effectively noise, and you can see which harmonics are dominant.
So this 3D graph always shows the entire recording time span. You don’t zoom into this graph. You don’t do a lot of detailed technical work in this 3D graph. It really is to give you an overview of the entire recording and lets you figure out very quickly which harmonics are the ones that you need to dig into further. And for that digging, you don’t use the 3D graph. This is just an overview.
And as David’s shown, you can rotate around, you get a better view to figure out which ones are high, as David pointed out here, with the fifth harmonic is the highest. Looks like the red is the seventh harmonic is the next highest, and that’s pretty common. So in many cases, the fifth and seventh are the highest on three-phase circuit. But you don’t know that in advance. That’s why you’re recording in the first place, to verify that or figure out what’s there.
Identifying Dominant Harmonics
So now that we’ve got our bearings, we know the fifth and seventh are high, can see on the scale that’s the vertical axis is in amps. So we see 40 to 50, 60 amps on the fifth harmonic, about 30 amps seventh harmonic. And we see some other harmonics are high.
If you rotate it around a little bit, you can see we have the 11th and 17th, but then we have, looks like the 17th and 19th. Those are all multiples of six plus or minus one that are very common for VFDs and that sort of thing. So there’s not a lot of surprises here, but that’s the point.
If there are surprises, this is where you’re gonna see it. If you saw a resonance in your system, you’d see something that may be at the 20th or 30th harmonic being much higher than expected. And without seeing the 3D graph, you’re gonna have to find the needle in a haystack going through all those individual harmonics. This is the quick way to get an overview of the entire recording session.
Moving From 3D to 2D Analysis
And now that we know the fifth and seventh, David can show you just jumping right into those with the tool here. So now we’ve picked fifth and seventh. Great graph. And now we have a lot more reasonable amount of data. Now we’re just looking at 2D graphs of just two harmonics.
And we can look at this in conjunction with RMS voltage or current or power and use the more powerful tools we have available in two-dimensional strip charts. We can zoom in, can overlay other pieces. We can do all those more advanced features that you don’t wanna try to do on a 3D graph.
So now that we’ve weeded down the data set from 50 harmonics to just two, life is much simpler, and now we’re putting our analysis effort where it’s best focused, on the harmonics that we saw that were high in this data file.
Summary of the Workflow
So the message here really is if you have a harmonic recording where you’re recording a lot of harmonics, start with a 3D graph and don’t spend a lot of time there. Just spend the time to figure out which harmonics are high and merit a further investigation.
Here, not all 50 harmonics are recorded, but again, we can see, you still see some dominant harmonics. Here we have pretty much all the odd harmonics that are probably worth a closer look. If you’ve recorded 50 harmonics, then odds are the majority of those are going to be close to zero, but you don’t know which ones they are until you check the 3D graph.
And so start with the 3D graph, get your bearings, figure out which harmonics need further investigation. Then either use the header report here, where you can see we’re clicking in volts or current magnitude to enable as many harmonics as you want in one graph. Or go to interval and do the same thing.
The 3D Graph as a Gateway
Well, that’s really the white paper in a nutshell. The key is to use the 3D harmonic graph, which is right here, as your gateway into looking at harmonic strip charts. And again, start with that, move it around, but don’t spend a lot of investigative time in that graph because you can’t zoom in. It’s not really meant to dig in directly. It’s kind of the gateway into the harmonics themselves.
And we’ve shown you some example files that are also in the white paper. And if you’re using our older ProVision software, it’s the same concept. There’s a 3D graph in there. But in general, regardless of how you’re looking at it, the 3D graph is the overview, and then the 2D graphs are the ones that you use for the more detailed work, where you’re looking at correlations between, say, a voltage third harmonic and current third harmonic or something like that to actually determine cause and effect or see if the harmonic levels rise when your cap bank switches in or out. Those sort of investigative pieces are done with the two-dimensional graphs, the standard strip charts.
Q&A: Delta-Y Connections and Harmonic Waterfall
And a good question. I would expect the harmonic waterfall to look at the source load as delta Y are connected and how… That really doesn’t change what the graph looks like. If the load is Y or delta, that might change which harmonics are present. If you have a delta connected load, you often don’t have third harmonic issues because they’ll be trapped, and the transformer is tripling harmonics. But whether it’s a Y or a delta, the 3D harmonic graph is really used the same way. Whatever harmonics are there, you’ll see, and that tells you which ones to go to.
Q&A: Harmonic Power Direction
And another question, can we turn the direction of power flow, and is the direction of power flow toward the… Yeah, it does show you something useful. Let me bring up a different presentation. This now goes kind of beyond what this paper talks about, but let me bring this up and show you. Because the harmonic power direction reveals something about who’s causing the harmonics, the customer or the utility.
So this is an example of doing that from a presentation. Each harmonic has its own real, reactive and apparent power flow, including a power direction. So here, for example, in the 2D bar chart, we’re looking at the harmonics for voltage and current. This is harmonic voltage. That’s harmonic current. This is harmonic power, and here at the fifth harmonic, we have about 15 to 20 volts of a fifth harmonic. We’ve got about 60 amps at the third harmonic, and we have about negative 1,000 watts at the fifth harmonic.
That negative power direction indicates or suggests that the load is injecting that harmonic current into the system. And if we’re positive, that would suggest that the utility is supplying harmonic voltage, and the load is drawing harmonic current because of that voltage.
Now, this can be helpful, but as you go up in harmonic number, this becomes less and less reliable. And you also have to make sure you have enough harmonic voltage to make a meaningfully large amount of power, so you’re not just measuring direction of noise. So if the harmonic voltage is small, you’re gonna get really small powers, and that power direction flow isn’t that meaningful. So for this technique to work, you wanna make sure that you have enough harmonic voltage to get a meaningful power, and also as you go up in harmonic number, it becomes less and less accurate.
Viewing Harmonic Power in PQ Canvas
Now, within PQ Canvas, on any waveform in PQ Canvas, you can get the harmonic analysis if you click that little harmonic button up at the top. And now you see the harmonic power at the bottom, and here it’s almost all positive. So in this case, it’s pretty clear, there’s not a lot of harmonic power in the first place.
Let me turn off the fundamental. There’s not enough harmonic current in this example to show that because the current’s very small, and this is a bad example. But this is how you get to that graph. You look at any waveform capture and then click on the harmonic button. Just like in ProVision, you get to that by opening up a waveform capture. Now, you can also record harmonic power or harmonic phase angle and power, but it’s easier to do this in the waveform capture.
Closing and Contact Information
Well, that’s all the questions we have now. Again, if you have a question later, give us a call anytime at 1-800-296-4120 or send an email to support@powermonitors.com. Or if you wanna learn more about harmonics, we have an entire one-hour class, a free class on harmonics. Just go to our website and sign up for that. And I will talk much more about harmonic analysis.
Well, thanks for attending, everyone, and everyone have a great afternoon.
