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Principles of Symmetrical Components Part 1D.

In this part we're going to investigate the difference between a balanced set of three phasors versus the unbalanced set, and some of the terminologies involved describing the balanced set versus the unbalanced set, which spills into symmetrical components. Let's get started.

These are the two phasors that were presented in part 1C, and by inspection I can tell you that this is an ABC system and this is also an ABC system. And both systems are balanced. But, we're going to make this system unbalanced and see how the phasors change. To make this an unbalanced set all we need to do is just grab these phasors and make the angle between IA and IC different than 120 degrees, or the angle between IA and IB different from 120 degrees. So, we could just rotate this, and as you can see as we rotate it the angle changes. Now, because the angle between these two guys are not 120 degrees and the angle between these two guys are not 120 degrees, this becomes an unbalanced set.

Now, let's put it back to where it was before. What if the magnitude of IB suddenly shrunk? So, now, IB looks something like that. So, the angle between IB and IC, well, that's 120 degrees, and the angle between IB and IA, well, that's also 120 degrees. But, the magnitude of phasors B is not equal to the magnitude of phasors C, and IB is also not equal to the magnitude of IA. So, because the magnitude of IB changes, this becomes an unbalanced set.

So, let's make the unbalance a little bit more severe. This configuration is also an unbalanced set of phasors. We're now going to cover some of the terminology that are involved describing balanced and unbalanced set of phasors, and how it spills into symmetrical comport. So, this is the balanced set of three phasors, right? Well, in a lot of the books and papers that we read, a balanced set is also described as a symmetrical system. An unbalanced is also described as an unsymmetrical system. So, we have the symmetrical system here and then the unsymmetrical system there.

Now, sometimes when describing faults, now we're talking about faults, we're describing faults or short circuits, sometimes we use the term symmetrical faults versus unsymmetrical faults. Or, we have a balanced fault versus an unbalanced fault. Now, these terminologies would describe how the phasors would look like if we had a balanced fault, or a symmetrical fault, or, if we had an unbalanced or an unsymmetrical fault. So, if you had a balanced fault we could expect the phasors for a balanced fault to look something like this. But, if we had an unsymmetrical fault or an unbalanced fault, we would expect the phasors to be unbalanced or look something like this.

So, that concludes part 1D. Now, in part two we'll actually go into how these symmetrical components are defined and constructed. If you haven't subscribed already please do so by clicking on the button that's on the bottom right corner of the screen. Look at the bottom of the page for additional information and as always visit generalpac.com for more power systems video tutorials. Thank you.

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