Shadowing Practice: 26 - How does harmonic phase shifting work including a detailed mathematical explanation to reduce s - Learn English Speaking with Video

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In this video we're going to talk about a subject that a lot of people ask questions about, harmonic cancellation with phase shifting transformers.

So with two variable frequency drives connected to a common bus and motors connected to those drives,

the harmonics that come out of those typical six pulse drives will have a current waveform that look like this.

So the drives will look like this and what happens is the total current is basically just two times that.

So it's one plus one equals two.

Before we put isolation transformers and phase shifting transformers in here to get cancellation, we're going to demonstrate how harmonics add up on power systems.

So we're going to go to a part of the system

over here where we're actually going to show you how that works.

And we're going to actually combine these harmonics from drives.

We're going to put two different drives on and show how those harmonics add up together.

So we'll turn one on.

We'll take a look at the waveform and you see the harmonics coming out of one of the drives.

And now if we take a look at the harmonic spectrum,

the harmonic spectrum from that has your typical fifth and seventh harmonics, what you'd expect.

And so the fifth harmonic right now is about 10 .9 amps.

Now if I turn on the second drive what we end up with is about twice that amount of harmonic current.

So as expected one plus one equals two and that's the harmonics that come out of both drives.

Now, what we're going to do is we're going to turn those drives off.

And we're going to go back to the paper

and we're going to describe what happens when we put two drives on but with phase shifting transformers.

OK.

So now with phase shifting transformers, we would put in this situation where we have,

for example, a delta y on one side, delta y on one side.

And this could be a delta delta, or in fact, it could be a delta zigzag, which effectively gives you a zero degree phase shift.

So you get zero degrees here, and you get 30 degrees here.

So the same harmonics come out of these drives that we saw in the other picture.

OK?

But what happens up here is this transformer has zero degree phase shift.

The harmonics come out the same.

This transformer, the harmonics kind of look like this, or the waveform kind of looks like this.

And so when you add these two together, we get what's not now a six -pulse system,

but rather a 12 -pulse system and we end up with a current that looks fairly linear.

So let me show you that in the actual waveforms that we can see from the two drives coming on.

So I'm going to turn this over to a combination where we put one drive on

and if we look at that situation, we have the isolation transformer where we're going around.

It's a delta -delta transformer.

Now if we look at the actual waveforms from that, the harmonics look very similar.

But if we look at the actual waveforms, the harmonics look the same.

But then when we put on the fourth drive, or the other drive, where we have the phase shifting, or the 30 degree phase shift,

you can see that now we have what's similar to a 12 pulse situation.

So now if I go to my harmonic spectrum, we actually have the fifth and seventh go away.

Now if we turn drive number one off,

what we're going to see is the harmonic currents come back from that drive that's now on,

the one that went through the delta Y transformer, and we can now see that the wave shape is,

as I showed you, a little bit different.

Now what's interesting about this is let's just look at one of the harmonics, the fifth harmonic.

Okay, and what we're going to do is we're going to look at the fifth harmonic here on phase A.

And the fifth harmonic is 9 amps at minus 62 degrees.

Now what we're going to do is we're going to turn that drive off, and we're going to turn drive number one back on.

and we'll see that the harmonic currents from that drive come in at about the same amount or magnitude,

about almost 9 amps again, but the phase angle is about 114 degrees.

So now if we put both of them on together, we put the other drive on with it,

now we get that fifth and seventh to cancel out, but your eleventh and thirteenth basically adds up together.

So going back to the paper now, let's talk about how that worked.

Again, we had no phase shift here, so we expect the wave shape to add up to be similar,

or to go through the transformer and look very similar.

This one here, the wave shape changed.

And this is a 30 degree phase shift.

So we're saying the 5th and 7th from here cancel with the 5th and 7th from here.

And what happens is we don't end up with 5th and 7th flowing this way.

So no 5th and 7th going this way, but we do end up with 11th and 13th, which ends up being this 12 -pulse system.

How does that work?

Well, if you take each harmonic order, the positive, negative, and zero sequence harmonics for each, we say plus, minus, zero,

plus, minus, zero, and that pattern continues.

Plus, minus, zero, plus, minus.

So if we look at just the fundamental, the fundamental we say is a vector,

a phasor, that rotates in this direction.

So phase A is at zero, rotates this direction, phase B follows, and phase C follows that.

So a negative sequence harmonic would actually rotate the opposite direction.

So how do we get the fifth and seventh to cancel from one side to the other?

First of all, all of these harmonics on the left side stay exactly the same.

The fifth harmonic on the right side is five times as fast as the 60 hertz, so the phase shift is 5 times 30 degrees,

but it's actually in the opposite direction.

It's a negative sequence harmonic.

It's in the opposite direction of the 60 Hertz.

So if the 60 Hertz is going ahead 30 degrees, and this one goes the other direction 30 degrees,

but times 5, we end up with 150 degrees this way and 30 degrees this way the net effect is 180 degrees.

It's like we always talk about two vehicles leaving at the same time, going opposite directions.

One goes 30 this way, 30 miles this way or whatever, and we say the other one goes 150 miles this way.

The difference in that is 180 miles.

In this case, we're 180 degrees out of phase.

And so what that actually means is when the fifth harmonic comes up from the bottom on this side, the fifth harmonic looks like this.

And when the fifth harmonic comes up from this side, it looks like exactly the opposite.

So those two added together in this path up here go away because they add up to zero.

And the seventh harmonic, because the seventh harmonic is a positive sequence harmonic,

it actually rotates the same direction as the 60 hertz.

So imagine 210 degrees or 7 times 30 going this way, 210 degrees.

And we're going the same direction or 30 degrees with the fundamentals.

So the net difference again is 180 degrees.

So as we look at the 5th and 7th coming up through power system, we're actually canceling out the 5th and 7th from both sides.

So as we wrap up, the key point here is we take two six -pulse drives, we put them through phase -shifting transformers,

and we create a 12 -pulse system.

Seems complicated, but at the end of the day, as we saw with the minus 61 or so degrees and 114,

115 degrees positive, you saw the fifth harmonic was exactly almost equal and opposite or 180 degrees apart, and that's how it works.

Thank you.

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Vocabulary and speaking notes for this lesson

This speaking lesson is built on the video “26 - How does harmonic phase shifting work including a detailed mathematical explanation to reduce s”. The speaker keeps coming back to these words: harmonic, drive, degree, phase, fifth. This video has 95 sentences and 1342 words to shadow. The speech runs for 9:00. The speaker talks at a steady 149 words per minute, a comfortable pace for shadowing. 85% of the words are among the 3,000 most common in English; the rest is worth studying before you start.

Key vocabulary in this video

15 words from the video worth learning, with pronunciation and meaning:

Word	Pronunciation	Meaning
delta noun	/ˈdɛltə/	The fourth letter of the modern Greek alphabet Δ, δ.
pulse noun	/pʌls/	A normally regular beat felt when arteries near the skin (for example, at the neck or wrist) are depressed, caused by the heart pumping blood through them; the…
seventh adjective	/ˈsɛvənθ/	The ordinal form of the number seven.
minus	/ˈmaɪ.nəs/	Made less or reduced by (followed by an expression of number or quantity).
sequence noun	/ˈsiː.kwəns/	A set of things next to each other in a set order; a series.
cancel verb	/ˈkæn.sl̩/	To cross out something with lines etc.
rotate verb	/ˈɹoʊ.teɪt/	To spin, turn, or revolve.
fundamental adjective	/ˌfʌn.dəˈmɛn.təl/	Related to a foundation, base, or basis; serving as a foundation.
spectrum noun	/ˈspɛktɹəm/	A range; a continuous, infinite, one-dimensional set, possibly bounded by extremes.
amp verb	/ˈæmp/	To amplify.
connect verb	/kəˈnɛkt/	To join (to another object): to attach, or to be intended to attach or capable of attaching, to another object.
isolation noun	/ˌaɪsəˈleɪʃən/	The state of being isolated, detached, or separated; the state of being away from other people.
cancellation noun	/kænsəˈleɪʃən/	The act, process, or result of cancelling; as, the cancellation of certain words in a contract, or of the contract itself.
complicated adjective	/ˈkɑm.plɪˌkeɪ.tɪd/	Difficult or convoluted.
angle noun	/ˈæŋ.ɡəl/	A figure formed by two rays which start from a common point (a plane angle) or by three planes that intersect (a solid angle).

Phrasal verbs you will hear

Word	Pronunciation	Meaning
add up verb		To take the sum of; to total.
add up to verb		To have a particular effect in combination.
drive off verb		To force to leave or go away.
go away verb		To depart or leave a place.
go back to verb		To stem from; to originate in.
go through verb		To travel from one end of something to the other.
come back from verb		To become successful, confident or effective again after an injury, setback, failure, embarrassment, etc.
come out verb	/ˌkʌm ˈaʊt/	To be discovered; to be revealed.

Pronunciation to watch

The speaker uses 27 contractions and reduced forms, such as we're, we'll, don't. Say them the short way, as you hear them.

The “th” sounds: seventh /ˈsɛvənθ/, eleventh /ɪˈlɛv.ənθ/, thirteenth /ˌθɝˈtiːnθ/
The “sh” and “zh” sounds: isolation /ˌaɪsəˈleɪʃən/, cancellation /kænsəˈleɪʃən/
Long words — get the stress right: fundamental /ˌfʌn.dəˈmɛn.təl/, isolation /ˌaɪsəˈleɪʃən/, cancellation /kænsəˈleɪʃən/, complicated /ˈkɑm.plɪˌkeɪ.tɪd/

How to practise with this video

Listen to the whole video once without speaking and note the words you do not know.
Shadow it sentence by sentence at normal speed, repeating each one until your rhythm matches the speaker.
Record yourself and compare with the original, paying attention to words like delta, pulse, seventh.

What is the Shadowing Technique?

Shadowing is a science-backed language learning technique originally developed for professional interpreter training and popularized by polyglot Dr. Alexander Arguelles. The method is simple but powerful: you listen to native English audio and immediately repeat it out loud — like a shadow following the speaker with just a 1–2 second delay. Unlike passive listening or grammar drills, shadowing forces your brain and mouth muscles to simultaneously process and reproduce real speech patterns. Research shows it significantly improves pronunciation accuracy, intonation, rhythm, connected speech, listening comprehension, and speaking fluency — making it one of the most effective methods for IELTS Speaking preparation and real-world English communication.

Shadowing technique: read the full step-by-step guide →

Shadowing Practice: 26 - How does harmonic phase shifting work including a detailed mathematical explanation to reduce s - Learn English Speaking with Video

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