 This is going to be a walkthrough of an auto transformer, a step-down auto transformer. What we have here, we have a 575 volts source, and we have a load connected across 35% of the windings. Which means that we are going to be using 35% of the voltage of 575 volts. Our load, our 12-ohm load, will see 201.25 volts. And all I did for that was to take 575 and multiply it by 35%, or 0.35. The next step is, let's get the current going through our load. We take, using Ohm's law, we use 201.25 volts divided by 12 ohms, and we get 16.8 amps. That's just by taking 201.25 volts divided by 12 ohms to get our 16.8 amps. Now we're going to try to figure out what our primary current is, which is the current over here, and then we're going to be left with trying to figure out what the current is across our common winding. Let's figure out the current over here first. What we're going to do, the easiest way that I know to do this, is to figure out what your VA, the power being used at this load is. Because remember with transformers, whatever the VA at the load is, has to be the VA at the source as well. VA in is equal to VA out. I'm going to take the voltage, 201.25 volts, and multiply it by 16.8 amps, and I'm going to get 3,381 watts at my load. Like I just said, whatever this watts is here, it's got to be the same over here, which will give us 3,381 watts on the primary side. Then to get our primary current, all we have to do is take 3,381 and divide it by 575 volts to get a current of 5.88 amps right there. Now if we have 5.88 amps on that side, and we have 16.8 amps on that side, the only thing we have left to figure out now is the current going across the winding from this winding right here. The current going through this part of the winding is in series with this source, so it's going to be the 5.88 amps. Now what I'm going to do is I'm going to move this current down to that point there. I'm going to move this current to this point here. Now I have 5.88 amps at that point. I have 16.8 amps at that point. I have this little node here. If I have 5.88 amps suddenly turning it to 16.8 amps, it has to be getting current from somewhere. That current's coming down here and adding to the 5.88 amps to give me the 16.8 amps. So all I have to do to figure out my common winding is to take 6.8 minus 5.88 and I get a current of 10.92 amps across the common winding. And that's all you have to do for a step-down auto transformer. They're not that difficult. Again, just a quick walk-through. You take the voltage, you multiply it by the tap setting, which gets us our voltage on this side. You take this voltage divided by the ohms of the load to get the current, which is 16.8 amps, through the load. Then I can take this voltage times this current to get this power. VAN is equal to VA out, so we can take that power and move it over to here. We take this power, which is the same, divided by that voltage to get that current. And then we take this current and that current and we subtract them from each other to get the current across the common winding. It's very similar in a step-up transformer, which will be the next video. See you there.