 video. I'm going to show you how we can determine the minimum KBA of a transformer based on the loads connected to that transformer. So let's take a look what we're dealing with here. We've got a dual winding, so we've got two on the high side, two on the low side. It's 28480 volt to 12240 volt, again depending on how we're connected. We've got the secondary side here connected as a 3-wire circuit. I have connected to the loads. I have eight kilowatts on this 120 volt side. I have three kilowatts on this 120 volt side. I have 15 kilowatts on this side, and I have 20 kilowatts on this side. Now in order to determine the KBA of this transformer or the minimum KBA that we have to have in this transformer, we need to figure out the current of each branch. So let's take a look what the currents are. We have an eight kilowatt load connected to the 120 volts. You can see that because the load goes back on the neutral. So we take eight kilowatts divided by the 120 volt coil there and we end up with 66.7 amps going through this branch. This one, we have a three kilowatt load connected to the 120 volt coil. Three kilowatts divided by 120 volts gives me 25 amps. Now this is the tricky one. We've got a 20 kilowatt load, but it is across... You've got two lines here, line one and line two. So this is a 240 volt load. So I'm going to take 20 kilowatts divided by 240 volts. Don't forget that. Do not get caught in the trap of using 120 again, and you're going to get 83.3 amps. And last and of course least, we've got this guy on this side, 15 kilowatts. Again, now he is connected to the 120 volt load because you're connected to the neutral there. 15 kilowatts divided by 120 gives you 125 amps. Now we've determined all the current going through each branch. We can determine what our line currents are going to be over here. Line one, let's figure out what it is up here. All I have to do is take this current and add it to this current and add it to this current. So 66.7 plus 25 plus 83.3 gives us 175 amps on this line. And then if we go down to here, we're just going to take the 83.3 amps and add it to the 125 amps, and we get 208.3 amps. Now while we're at it, why don't we determine what the neutral current is? It's not really necessary, but it's just a good habit to get into. If I have 208.3 amps there, but I have 175 amps there, that means that I had the 208.3 traveling along here, and suddenly I have 175 where did it go? It went along the neutral, and that neutral current is going to be 208.3 minus 175, which gives you 33.3 amps on the neutral. Now we're ready to determine the minimum kba of this transformer. In order to determine the minimum kba, what you have to look at is these currents here. I have 208.3 amps running along this winding, and I have 175 amps running along this winding here. To determine the minimum kba, what you have to do is take the larger of the two currents, in this case it is 208.3 amps. That means that this winding here has to be able to handle 208.3 amps across it. Now when we're dealing with these dual winding transformers, these windings are generally equal, so we have to have this winding rated at 208.3 amps, which means that this one's going to be rated at 208.3 amps as well. That's what its rating is. Now with this connection, we are only using 175 amps, so we have not exceeded the rating. That's the important part of this one here. What we're going to do is take 208.3 amps, we're going to multiply it by 120 volts because that's what the coil is. That will give us the kba of one winding, and then we're going to multiply that by two because we have two windings. In this case, 208.3 times 120 times two because of the two windings gives us 50 kba. I know this is sounding redundant, but let me show you again. 208 across this winding, because that's the higher of the two currents, times 120 volts, and then we have to multiply that by two because we have two windings there. It's 50 kba. Now I know what you're thinking, or some of you might be thinking, is that, well, with transformers, power in is power out, so why can't we just add up all our powers, which is 46 kba in this case, and say, okay, well, the minimum kba that this transformer has to be able to handle is 46 kba, right? Well, if we look at that, if we take that 46 kba, that means that we have to split the kba equally across each winding. Are you digging what I'm saying here? 46 kba is for both windings here. That would give us 23 kba on this one and 23 kba on this one. Now with this rating here, let's determine what the current is going through these windings, or what's the rated current that this transformer has to be able to have. So I take 23 kba and divide it by 120 for this one and 23 kba divided by 120 for this one, and we're going to determine what the maximum current is that you could safely put through this transformer if this was a 46 kba transformer. Okay, there we go. This one here, we get 23,000 divided by 120 gives me 192 amps. Over here, we have 23 divided, 23,000 divided by 120 gives me 192 amps as well, obviously, because it's a dual winding transformer. Now looking at here, I've got 192 amps. That means that this winding here is rated to handle 192 amps. I see this current up here is only 175. So you're thinking, oh yeah, we can totally handle it. And yes, you can. This side definitely can. But if you look on this side, the 23 kba, it's only rated to be able to handle 192 amps. Well, what do we have going through it? 208. What's going to happen there is eventually you're going to let all the smoke out of those windings, and we call that goblasal flam. It's not good for the transformer, you're overloading this winding. And that's bad, it will eventually burn out. It is not 46 kba, that is why we have to rate this transformer for 50 kba so that this winding here can handle the 208.3. And that's the minimum kba, you're not going to generally just kind of rate your transformer right to the minimum, you're going to get a bigger size than a 50 kba, because if I wanted to add anything else in parallel with this load, it's going to be a problem. But that's not our problem today. Our problem today was just to determine the minimum kba. So remember, work out which each line current is, you're going to take the higher of the two line currents, you're going to multiply it by the winding voltage to get the kba, and then you're going to multiply that by two if you have a dual winding transformer like this, and that will give you your minimum kba for a dual winding transformer.