What do you mean by, "Harmonics are not a problem unless they are a problem?"

So we like to say harmonics are not a problem unless they're a problem. So what the heck does that mean?

Well, here's the thing. Harmonics are like the new normal. There's a lot of non-linear loads out there that create harmonics-- fluorescent lights, LED lights, variable frequency drives, all kinds of rectifiers, your battery charger, your computer. All those things create harmonics. So that's kind of the new normal.

What we're saying by harmonics are not a problem unless they're a problem is do they cost you money, and does it cause issues within your home, your facility, your process, or your manufacturing or industrial process or maybe in your utility system. So as we look at it, let's take a look at this graph, for example.

Now I've seen this top waveform actually have loads operate perfectly fine on that, even though that voltage waveform is completely screwed up because of harmonic distortion. But that was on an oil rig in the Gulf of Mexico. Now if I take the bottom waveform, and that looks like a pretty clean sine wave and it's only distorted by a couple percent, I've actually seen a very good, pristine laboratory where they had very precise equipment, and it couldn't work with that amount of voltage distortion. So it even needed better than 2 and 1/2% distortion, let's say.

So the answer is it depends on the system as to whether the voltage distortion is going to get you in trouble or not. Now if we look at current distortion, we think about that causes heating and other things, we have to recognize what that really can do to your system. So again, harmonics are the new normal. You have to really get to the point where you understand what costs you money before you decide if it's a good or a bad thing.

And a lot of people-- one of the things I tell a lot of people is don't do anything. You don't really have a problem. Just because you see harmonics, maybe you have a new meter that can show you the waveforms, or somebody printed out a TGD report for your system or a plot of the RMS and the total harmonic distortion over time. Just because you have that distortion, there does not necessarily mean that you're going to have actual problems.

And then the other thing is current distortion without resulting voltage distortion is typically not an issue. So let's say you have a small load on a very big system or a stiff source as they say, very low impedance. It's going to yield low voltage distortion. So that's typically not going to be a big problem. So as we look at things like this, again, the problems that harmonics create-- overheating, misoperation, audible noise, qualifies correction issues, things like that, resonance-- those are legitimate problems, and you have to be concerned. But otherwise, that's why we say harmonics are not a problem unless they're a problem.

So let's switch over to the graph here. I want to show you something. I just want to show you what I mean by putting a small load on a big system. So for example, if I have a utility system, I have a transformer, and I decide to put a drive in front of my motor here, and my motor is 30 horsepower, and my drive is 30 horsepower, now I expect to see out of that drive a waveform that looks something like this. That's just my characteristic six pulse drive.

And it's going to have a spectrum that looks something like this. I have a fundamental. I have a fifth thermionic. I have seventh thermionic. I have 11th thermionic and 13th thermionic and so forth. And they decrease as we go up in frequency. So again, 1, 5, 7, 11, 13 and so on. So we expect those harmonic currents. Now what's interesting is how much does that screw up this bus voltage because, in reality, that's really what I care about. The drive draws what the drive needs, and it takes the current that it wants.

But what if I have, let's say, some other computer equipment over here or perhaps another across the line motor over here. Well, how much I screw up this bus voltage affects the way that those loads operate. If this transformer here, for example, was 30 KVA, I probably will have a problem. And in fact, I'll start off with a nice, clean sinusoidal voltage. And with that current, my voltage distortion might be pretty apparent, and it might really screw it up.

But what if this was not a 30 KVA transformer, what if this was a 3 MVA transformer? Well, in fact, this is such a small percentage load based on this. And why do I care? Because this transformer has an impedance. And when this current flows across this impedance, voltage distortion equals current distortion times harmonic impedance, then I will start to care.

So if I have a very low impedance, big transformer, my bus voltage is now going to be still very nice and clean. If I have a very small transformer, high impedance, my bus voltage is very distorted. So again, harmonics are not a problem unless they're a problem. And we really have to understand what's important when we take a look at what those problems could be as to whether or not I'm concerned.