쉐도잉 연습: 26 - How does harmonic phase shifting work including a detailed mathematical explanation to reduce s - 영상으로 영어 말하기 배우기

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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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이 말하기 레슨은 영상 “26 - How does harmonic phase shifting work including a detailed mathematical explanation to reduce s”을(를) 바탕으로 합니다. 가장 자주 반복되는 단어는 다음과 같습니다: harmonic, drive, degree, phase, fifth. 이 영상에는 섀도잉할 문장 95개와 단어 1342개가 있습니다. 말하는 구간의 길이는 9:00입니다. 화자는 분당 약 149단어의 일정한 속도로 말해서 섀도잉하기에 편한 속도입니다. 단어의 85%가 영어에서 가장 많이 쓰이는 3,000단어에 속합니다. 나머지는 연습 전에 미리 확인해 두세요.

이 영상의 핵심 어휘

영상에 나오는 익혀 둘 만한 단어 15개를 발음, 뜻과 함께 정리했습니다.

단어	발음	뜻
delta 명사	/ˈdɛltə/	델타
pulse 명사	/pʌls/	맥박
seventh 형용사	/ˈsɛvənθ/	일곱째
minus	/ˈmaɪ.nəs/	빼기
sequence 명사	/ˈsiː.kwəns/	순서
cancel 동사	/ˈkæn.sl̩/	취소하다
fundamental 형용사	/ˌfʌn.dəˈmɛn.təl/	기본적
spectrum 명사	/ˈspɛktɹəm/	스펙트럼, 분광
connect 동사	/kəˈnɛkt/	잇다, 연결하다
isolation 명사	/ˌaɪsəˈleɪʃən/	격리, 고립
cancellation 명사	/kænsəˈleɪʃən/	취소, 삭제
complicated 형용사	/ˈkɑm.plɪˌkeɪ.tɪd/	복잡하다
angle 명사	/ˈæŋ.ɡəl/	각, 각도
frequency 명사	/ˈfɹiːkwənsi/	빈도
wrap 동사	/ɹæp/	싸다

영상에 나오는 구동사

단어	발음	뜻
go away 동사		떠나다, 떠나가다
come out 동사	/ˌkʌm ˈaʊt/	나오다
come up 동사		올라오다
wrap up 동사		시마이치다

주의할 발음

화자는 we're, we'll, don't 같은 축약형과 약화된 형태를 27번 사용합니다. 들리는 대로 짧게 발음하세요.

“th” 소리: seventh /ˈsɛvənθ/, eleventh /ɪˈlɛv.ənθ/, thirteenth /ˌθɝˈtiːnθ/
“sh”와 “zh” 소리: isolation /ˌaɪsəˈleɪʃən/, cancellation /kænsəˈleɪʃən/
긴 단어 — 강세 위치에 주의: fundamental /ˌfʌn.dəˈmɛn.təl/, isolation /ˌaɪsəˈleɪʃən/, cancellation /kænsəˈleɪʃən/, complicated /ˈkɑm.plɪˌkeɪ.tɪd/

한국어 화자가 어려워하는 소리:

/f/ — ㅍ(/p/)으로 바꾸지 말고 윗니를 아랫입술에 대기: fundamental /ˌfʌn.dəˈmɛn.təl/, frequency /ˈfɹiːkwənsi/, transformer /tɹænsˈfoɹməɹ/
/v/ — ㅂ(/b/)과 구별하기: seventh /ˈsɛvənθ/, variable [ˈvæɹ.i.ə.bl̩], vector /ˈvɛktɚ/, eleventh /ɪˈlɛv.ənθ/
/r/과 /l/ 구별하기: linear /ˈlɪn.i.əɹ/, variable [ˈvæɹ.i.ə.bl̩]

이 영상으로 연습하는 방법

먼저 말하지 않고 영상을 끝까지 듣고 모르는 단어를 적어 둡니다.
보통 속도로 한 문장씩 섀도잉하고, 화자의 리듬과 맞을 때까지 반복합니다.
자신의 목소리를 녹음해 원본과 비교하고, delta, pulse, seventh 같은 단어에 특히 주의합니다.

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쉐도잉 연습: 26 - How does harmonic phase shifting work including a detailed mathematical explanation to reduce s - 영상으로 영어 말하기 배우기

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