Does a delta-wye transformer cancel all harmonics?

A good question we get a lot is if I put a delta-wye transformer in will that cancel all my harmonics.

Basically, to answer the question of whether delta-wye transformer will cancel all the harmonics, it won't. It will recirculate the third harmonics in triple and harmonics back to the load. But if you use it in combinations with other transformers like we've shown in some of the phase shifting videos you can do some cancellation. Let's look at this graphic and see what happens with delta-wye transformers.

Let's watch the blue arrow. It is going out Phase-B, and it's going to come back on the neutral. On Phase-A the red one goes out comes back on the neutral. The black one goes out comes back on the neutral, so we see those triplin harmonics additive on the neutral. We've talked about that in other videos. On the primary we see the blue and the red and the black and they circulate in the Delta. The reason they circulate is if they're balanced on the secondary, say for example 10 amps 10 amps and 10 amps on the primary through the ratio, the difference in the current is zero at these node points. So, the current that flows out on the phases on the primary is zero. If you look at a delta-wye transformer and if you look at what's going on inside the transformer, we can see which harmonics would be cancelled in those cases.

Let's say a delta-wye here and we have fundamental 3D 5th, 7th, 9th, 11th and 13th for example, so 1 3 5 7 9 11 13, you're going to see all those are going through the transformer. If I get rid of the third and the 9th, look what I'm left with: the 5th, 7th, 11th, and 13th. So, in terms of on this side, I would see all these harmonics on this side. I would see the fundamental fifth, 7th 11th and 13th. That looks a lot like NP plus or minus one for a six-pulse drive, which gives me 5th and 7th, 11th, and 13th, 17th and 19th. On this side the current would look like this, like a single pulse. And on this side the current would look like this. It's very interesting. This is all your odd harmonics 1, 3, 5, 7, 9, 11 so forth. This is your 5th, 7th, 11th, 13th. It looks like a drive. So, on the 480-volt side typically in this situation we're going to have something that looks like drive current. On the secondary side we see this switch mode, power supply or LED light waveform. So, when you look at it does the delta-wye transformer trap or circulate back all the harmonic currents? No. It only takes care of the triplin harmonics and then in some of the other videos we talk about how we can eliminate some of the harmonics doing phase shifting.