Hus:
In this video, we’ll compare starting torque and starting current off a three-phase induction motor with four different starting circuits. Let’s get started. Hi, I’m Hus. In this video, we’ll compare the starting torque and starting current off a three-phase induction motor with four different starting circuits. Direct Online, Star Delta Starter, VSD, and Soft Starter. Before we start the measurements, let’s understand our setup. On this side, we have a test set up with a three-phase induction motor with six terminals. It’s connected to a torque sensor and we have a clamp meter here so we can measure current. On this side, at the moment we have a motor starter prac box where we’ll use VSD, Direct Online, Soft Starter, and then we’ll replace this box with a control circuit prac box where we will do a Star Delta Starter. As we go through our experiments, I will take measurements here, that way I can share it with you at the end of the video.

Let’s take our first measurements with Direct Online circuits. And before we start taking measurements of Direct Online, there’s one thing we need to understand. For comparing all the starting torques, we would need a fixed or a standard load. In this case, we don’t have one because it’s just a no load circuit. To be able to measure it more accurately, I’m going to hold the shaft, which will give me a locked rotor. So it’ll give me a locked rotor torque, but in this case, we’re really just comparing what will be the difference between each of these starting circuits when they start up. So assuming that the load is going to be something that’s just going to lock the rotor, what’s going to happen? That’s what we’re trying to work out here. I understand that the locked rotor torque usually is a lot higher than the starting torque, but in this case to keep it consistent, we’re going to use that method.

All right, let’s take the measurements. So I’m going to lock the rotor and turn on the motor. As we do, we can see that the torque jumps straight to about 0.13, 0.14 and the currents jump straight to about 630 milliamps. Let’s record these values. Let’s change our circuit to Soft Starter and see how that will operate. All right. Our Soft Starter circuit is ready. Now the setting wise, I have dropped the starting time to the highest and the initial voltage to the lowest, which will then give us the longest ramp up time. So let’s see how that works. All right, let’s measure the torque first, then we’ll look at the current. So 0.04, 0.05 is where our starting torque is and the locked rotor torque gets to about 0.13. Let’s repeat that for current. About 0.48, 0.49 and that’s our starting current and the locked rotor current is about 0.61. Let’s record that. Let’s change our circuit to VSD and see what we measure.

All right. Our VSD circuit is ready. The settings we have set the frequency to 50, which is the maximum. The ramp up time, I’ve set it to eight seconds and ramp downtime is three seconds. We’re not worried about the ramp down. It’s the ramp up that we’re most concerned with. We are using the local connection, so we’re just going to press this start button. Let’s take the measurements. So the way we’re going to do it, we’ll start off with the torque measurement first and then we’ll turn it off and then we’ll do the current measurement after. Okay, let’s start. As I turn it on, I can see that it ramps up very slowly. It starts at about 0.02 and then ramps up to about 0.129, 0.13. So that’s our locked rotor and starting torques. Let’s look at our current measurement. Okay. Current starts up at about 40, 50 milliamps and goes all the way up to 610 milliamps. I’m going to change this box to control circuit prac box so we can do a Star Delta Starter circuit and then take our measurements.

Now that we’ve got our Star Delta Starter circuit connected with the control circuit prac box, let’s take our measurements. We’ll start with the torque measurements first. So I’ll hold the shaft, turn it on, start at about 0.05 and switches to about 0.13, 0.135, about 0.14. Let’s take that. Let’s measure our current. In star we have about 0.36 and when it clicks the delta, it’s about 0.62. Now that we’ve got our readings, let’s compare them. So in Direct Online, we see that the starting torque and the locked rotor torque is the same, and our starting current and the lock rotor current is the same. Again, it wasn’t a load. We were locking the rotor just to keep it all consistent so we can take our measurements. So that’s our Direct Online results. If we look at Star Delta Starter, our starting torque was 0.05 newton meter and the starting current was about 362 milliamps.

Our locked rotor torque matched with the previous one because the motor is still the same and the locked rotor current is quite similar as well. Same reason because the motor is still the same. With Soft Starter, we had a good ramp up 0.05 newton meter, got to about 480 milliamps as our starting and got to about 0.13 newton meter, which is close to what we had for Direct Online, and the current is quite similar as well for locked rotor. Variable speed drive start at about 0.02 newton meter and about 50 milliamps and ramped up to 0.13. And the locked rotor current was about 609 milliamps. I hope you enjoyed this video of comparing starting torque and starting current of a three-phase induction motor with Direct Online, Star Delta Starter, Soft Starter, and DSD. If you have any questions or feedback, please feel free to contact us. Thanks for watching.