Husnen (Hus) Rupani:
If you teach AC circuits or G102, then you know that the hardest part of that is to finding the right components that will cover all the aspects of that subject. To solve the problem, we’ve designed this AC Pracbox.

Hi, I’m Hus, and in this video I will tell you about how this AC Pracbox can make your life easier when teaching AC theory.

Let’s get started. If I turn this on, there’s only one IEC cable that powers this AC Pracbox. So first, let me show you where all the components are and what they are. So here, we’ve got three 50 watt resistors, we’ve got 20 ohm, 10 ohm, and 5 ohm resistors here. Here, we’ve got three 100 watt resistors, all of them 33 ohms. These are all capacitors so 80 microfarad capacitor, 53 microfarad motor start capacitor, three 22 microfarad capacitors, and one 220 microfarad electrolytic capacitor.

On this side, we have three button holders, and here we have four toggle switches that are not connected to anything, so you can use it to control the circuit that you connect. On this side, we have three contactor cords that we’ve converted into inductors, so these are your inductors, resistors, capacitors, and some lamp holders for extra load. We have a meter here that can measure power voltage, current, power factor, frequency and energy all in one without pressing any buttons so very powerful. Let’s now connect a circuit or a few circuits and see what this Pracbox can do.

You can see right now I’ve got this power supply single phase, a variable set to 10 volts, powering up the 10 ohm resistor and that’s giving about 0.9 amps of current, which is understandable, Ohm’s law. And you can see the power factor is showing power factor one. So you can show that right at the start with the RLC circuits. This is the R part. Let’s go to the L part and see how that works. So if I change my voltage to 15 volts, I can see that at 15 volts I’ve got this inductor, which is 18 ohms and 92 millihenry inductor getting about 0.4 or 450 milliamps of current and 0.5 of power factor here so you can show them the power factor, you can show them how much P it’s drawing. If you multiply voltage with current, you get your apparent power, and from the power and the apparent power, as in the true power and the apparent power, you can find the reactive power and you can find the power factor in calculation as well to confirm your values.

If I move that to a capacitor, for example, I can see how there is 17 volts. It’s drawing about 450 milliamps of current, but the power factor is zero and the power, the true power itself is also zero watts. That shows that the capacitor is not drawing any power, but it’s drawing current, which means you’re still supplying current to it, but it’s not doing anything for you. Everything is reactive. That is a very important concept to show just with some circuits.

Let me quickly show you power factor correction as well. So right now, we’ve got that inductor that has a power factor of 0.5. Let’s correct this power factor with a 22 microfarad capacitor. You can see how my power factor went from 0.5 to 0.6 or 0.7 and the current went down, but the overall true power stayed the same. Very important concept, can be very complex but makes it so much easier to just show it here. We can go even higher. I can correct the power factor with the 80 microfarad capacitor and you can see how it went from 0.6 to 0.9 and that power went up just a little bit, but you can see how the overall current went down.

That also shows that if you don’t correct it properly or if you need to correct it even better, then you can use a better capacitor or a higher capacitor. If you went even further, if you were to fix the power factor with a 220 microfarad capacitor, you can see now I’m drawing even more current and I’ve got more true power and the power factor went down because now I’ve got 220 microfarad, which is over correcting the power factor of that circuit. Very important concept, again, not very easy to explain just by the diagrams and writing things, doing practical makes it so much easier.

That’s the single phase side. What about the three-phase side? So let me show you quickly how we can use this to show three phases as well. Now, we have a star connected circuit here powering these three lamps. Let’s turn them all on, see what we get. So you can see how we’ve got all of these lamps connected. On this side, I have wired the neutral wire to a switch, which means that if I turn it on and off, the neutral will connect and disconnect.

Right now the neutral is connected, and to prove that I will turn one of the phases off and you can see how there is no noticeable difference in the other two loads, which makes sense. But if the neutral was disconnected, if all three loads are there, no problem. But if one of them goes, you can see how those two dim a little bit. If I turn that on, you’ll see it gets brighter. So that shows that there is some sort of imbalance in the circuit if I did that. In fact, with neutral disconnected, one phase is still on and you can see all of them turned off. But if the neutral was there, then even one phase could work. Again, a concept very easy to explain when you have a practical setup like this.

Let me now change this to find out what is the power and the voltage and the current going through each of these loads, so I’ll turn this off. Now, this is also called a single wattmeter method. So if I turn them all on, you can see how the meter is showing that per phase, I’ve got 25 watts of power. Per phase. I’m getting 23.5 volts and one amp drawn by that lamp power factor of one, which also makes sense because it’s a heating load.

Let’s change this circuit to delta and then see what measurements we get here. Now for delta, we don’t need neutral, so I’m going to disconnect that. Let me change the whole circuit. So now I’ve got these lamps connected in delta. Let’s see the difference before measuring anything. It’s a clear difference here how the lamps are a lot brighter than what they were when they were connected in star so you can see how the voltage over there is increased. If I do single phasing now, you can see how two lamps get dim, but one of them stays bright. If I do that, you can see that here as well. If I turn two of them off, then the whole thing turns off.

Let me do a single phase single wattmeter method here as well and see what we get. Okay, delta connected in single wattmeter method. We can see how the voltage is 40 volts and the current is 1.5 amps and the power is 56 watts so almost 60 watt power. Power factor is still one. But we can see how with more voltage we’ve got more current and overall you’ve got brighter lamps.

What happens in single phase? So let’s turn that off and you can see how when there is a single phasing, the voltage dropped to 19 or almost 20. So that’s half of what we had. Current drop down, power went down three times as well, and the power factor is still the same. We can see that.

So you can see how this makes it so much easier to explain the concepts of three-phase as well. You can even use these three resistors in three-phase or you can connect these resistors in parallel or series to change the phase to create an imbalance, so there’s a lot you can do in just this setup here. In fact, everything that is there in G102 that needs some practical explanation is covered in this AC Pracbox.

If you have any questions about the AC Pracbox or any of our products, please feel free to call me on this number or send us an email here.

Thanks for watching.