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Okay, so, now that we've written all these terms here and kind of gotten very complicated, let's really focus on what these equations really mean, okay? There has to be some meaning to these equations so let's talk about it.

This is something that took me a lot of time to really understand and hone, okay?

So, when we talk about, let's start with this, right? The power of the ith bus, Si. So, we're talking about this particular part here, right? The apparent power of the ith bus. What do we actually mean?

Well, that essentially means that it is the net real and reactive power entering the ith bus. So, it is the net real and reactive power, entering this ith bus.

We know that if there was something at this ... Bus one was connected to another bus, then if power entered bus one from this other bus and then if power left bus one to but two,

then the power entering minus the power leaving, that's the power that we're calculating by this particular equation.

Okay? It's the net real and reactive power that's entering or leaving or however you want to call it, of the ith bus or bus one in our example.

The other thing is, we said that power of the ith bus is equal to this term here, right, the power generated. Now, I didn't allude to this before, but now address it here.

This term essentially means that if bus one, we had a generated on bus one, right? So this generator is now pumping power to bus one.

That is accounted by this term here, and then if this bus one also had some sort of load, right? It had some sort of load then this term here accounts for that.

So, what we're essentially saying is that Pgi, okay, we're now talking about this term here, so P-G-I. Pgi and, right here, Qgi, Q-G-I,

now Pgi and Qgi are the scheduled real and reactive power, generated at the bus. So Pgi and Qgi is this generator here. If we had some sort of generator that was pumping power, then that is the scheduled real and reactive power that is generated at the bus.

Then, Pli, right, and Qli is equal to this load that represents this load here. This load had some sort of power that was consumed and that power's broken up into two components, then those two components would be these two terms here. The Pli and Qli is the scheduled power demand of the load bus.

So, it's the power demand that's already scheduled, that we already know about and it is represented by these two equations here.

So, remember Si is the net real and reactive power that's entering this bus. It's everything that's going in minus everything that's coming out so it's the net real and reactive power.

We would have to calculate the net real and reactive power of bus one, we would have to calculate the net real and reactive power of bus two, and all of the buses in our system.

We want to know the power entering into the bus, the power generated at the bus, the power consumed, which is a load, at the bus, and the power output of the bus.

All of these terms are combined to give us what we called a power flow. That concludes this video tutorial, so that concludes the final part of what we call the Power-flow Equations in the power system.

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If you have any questions, please go ahead and ask them but I request that you ask them by clicking on the forum link, the forum, on the bottom of this video tutorial.

URL that links to this forum, in this forum, you're able to add very detailed question about power flow and get a very intuitive understanding about what all of these voltages and currents actually mean.