# Symmetrical Components - Free Video Tutorial



## Complex Imaginary (Jul 22, 2011)

Someone on this board requested a tutorial video for symmetrical components. We hope these three videos will be a big help to those studying for the Power PE exam. As we all know, symmetrical components is one of the more "out there" concepts on the PE exam. If anyone else has any requests for other topics, please let us know and we'll do our best to satisfy.

Here are the links to the symmetrical components videos:

PE Power Exam - Symmetrical Components (part 1)

PE Power Exam - Symmetrical Components (part 2)

PE Power Exam - Symmetrical Components (part 3)

By the way, the rest of our Power PE videos can be found on our youtube channel here:

Complex Imaginary Youtube Channel

All the best in your studies,

Josh

http://www.compleximaginary.com


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## mudpuppy (Jul 23, 2011)

I use symmetrical components every day. Are you saying I'm "out there"? :huh:

(just kidding)


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## EEVA PE (Jul 23, 2011)

Good video on the symmetrical components, but I thing the positive sequence shown is negative sequence. The arrows of rotation need to be switched. I look at it from the point of view on the x-axis @0 degree and watch the rotation. I see as shown for positive sequence a-c-b. This should be a-b-c for it to be called positive sequence. For the negative sequence, I see a-c-b which is correct. Someone please confirm, maybe I am wrong. I thought I had this nailed down.

3 months and 1 week to go.


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## mudpuppy (Jul 24, 2011)

You are correct. To my eye, the positive sequence phasor rotation should be the other direction (counter-clockwise).


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## Flyer_PE (Jul 24, 2011)

mudpuppy said:


> You are correct. To my eye, the positive sequence phasor rotation should be the other direction (counter-clockwise).


I agree. Both networks should be rotating counter-clockwise. The difference being that the positive network sequence is a-b-c and the negative sequence network is a-c-b.


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## Complex Imaginary (Jul 24, 2011)

Good points everybody! We strive to be as accurate as possible in our videos. Unfortunately, this is a relatively complicated issue that we tried to avoid while using as simple and clear visual aids as possible.

Let us quickly present the confusing elements in play:

When we talk about rotations in 3-phase power, there is no single standard that captures all facets of the math, physics, and industry language. So that's a difficulty in presenting the content of this video. We didn't want this issue to take over focus on the symmetrical components theory. In the end, this rotation issue can be confusing enough to warrant its own video tutorial. We will plan on making a video dedicated to this in the future. In the meantime, we thought the following links were helpful in showing the difficulty of this topic:

http://www.marcspages.co.uk/pq/3120.htm

http://www.eng-tips.com/viewthread.cfm?qid=8600

Now let us explain the reasoning behind our visualizations in the videos:

The rotation symbol that is shown for the symmetrical components in our videos are NOT referring to any kind of motor/shaft/physical reference. This symbol is only there to emphasize the point that the positive and negative sequence vectors are oriented in the opposite way. We're showing a quick, shorthand visual to highlight this - something to guide the eye. That symbol could have been left out, and all of our explanations would remain the same. We left it in because we felt people could miss the ABC, ACB difference in the vectors drawn too easily (since the two "wye" shapes look very similar otherwise). It is only a visual aid to help with the arrows shown on the video.

These are our thoughts on this issue. If you think our videos are too confused because of this, let us know and we'll change them. We're are trying to help you out, not confuse you. Thank you very much for such close attention to our videos, we appreciate it.

Josh

http://www.compleximaginary.com


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## R2KBA (Aug 2, 2011)

I am pleased with these videos, especially the 3rd one. Thanks for sharing them.

About the issue with the direction of rotation, this is how I think of it (and please correct me if I am wrong): If you mentally rotate the phasor diagram CCW, you should eventually see "ABC" pass through the 0 degree point for positive sequence, and you should eventually see "CBA" pass through for negative sequence.


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