Can I increase my linear load to cancel my harmonics?

So a lot of times, we're asked the question, if I increase my 60-hertz load, won't that decrease my harmonics?

And in fact, it's interesting. You can decrease the percentage THD on the current, but you're not really changing your harmonics as far as how the power system responds to those harmonic currents and how the voltage is distorted based on those harmonic currents. So let's take a look at this equation. Voltage distortion equals current distortion times harmonic impedance.

My current distortion here is in amps. My voltage distortion is in volts. And my percentages of my voltage distortion are not going to be affected if I change my current distortion as a percentage. And I'm going to show you an actual example of that.

So let's take a look at a power system here. I'm going to switch over, put the camera on, and actually turn on a bunch of VFDs. So as I add these drives, as I add these drives, you can see that the current is fairly distorted, and the voltage is fairly distorted. So let's take a look at the percent distortion THD of the voltage first.

We'll let that settle out. So with all four drives running, we're at about 6.4-6.5% distortion. Let's look at the current distortion. And so our current distortion right now is on the neighborhood of 38.7 or 8%. Now, I'm going to add a significant amount of linear load to that, and you'll see that my current distortion dropped by about 10%.

Let's look at our voltage distortion. So our voltage distortion is still about 6.4. I'll turn that load off while we're on this screen just to show you the difference. And it doesn't change at all. I'll add that load back in.

OK. And now, let's go back to the current distortion. So we're at 28.1%. Let's look at the fifth harmonic. And if you look up in the top left here, we have 41 and 1/2, 41.7 amps of fifth harmonic current. The percent distortion for the fifth is 26.6%. If I turn off my linear load, my distortion of my fifth went up to about 37%. And you can see the fifth harmonic increase just slightly. That's more of a function of loading on the power system.

So my increase in 60-hertz current here really did very little or didn't change at all my harmonic current distortion and, in fact, did no change to my voltage distortion. So, again, I'll leave it there, but just, basically, to wrap up, if I add current as a load in terms of 60-hertz current, I'm not going to decrease my actual harmonic current on my system. I'm only changing the percentage.

I will not affect my voltage distortion, which is really telling based on that equation of voltage distortion equals current distortion times harmonic impedance. So, again, to answer the question, adding 60-hertz current doesn't change my harmonics on my system, only that percentage, and that percentage can be misleading. So just be careful of that.