Ansys Maxwell: Coil Models pt 1 - Geometry

Hello everybody, Ian from Ozen Engineering here. Welcome back to the Beginner's Guide series. Today, we're going to start a discussion about how coils are modeled in Ansys Maxwell.

Introduction

The reason I think this is an important topic to cover is because if you're like me, you probably picture something like this when you think of a coil. Physically, it might look like something like this:

• This coil is commonly used as a heating element.
• If you've done a lot of work with electronics, you might picture something like these common inductors.
• If you work with motors, you might picture coils that look like these.

There are a lot of different coils out there and different types of coils. But then you learn how to model these coils in a finite element environment, and you're shown something like this. And you're told that this is a coil, and that these are coils. You want to try to look at these coils in a different way.

Modeling Coils

You want to learn how to model coils around a stator in your motor, and you're shown something like this. When I started learning Maxwell, I saw these simplified objects and I wasn't completely convinced that they would accurately model the more complex objects. Luckily, at the time I was in a lab where I could just test this out.

So I cut a little form out of PVC and started wrapping some wire around it, and I made my own coil that I modeled in Maxwell. When I ran the simulation and tested the coil by measuring the inductance with an Agilent PCR meter, the results agreed with impressive accuracy. That said, in retrospect, I probably stumbled into a certain amount of luck. It's not very common to have your simulation agree with your experimentation to this degree.

But I then ran another experiment to measure the induced voltage on my coil caused by a changing current in a nearby coil, and it had great accuracy again. So at this point, I was feeling more comfortable with the cylinder as a representation for a coil, but I still want to know how these two objects compare.

Simulation and Comparison

More specifically, I'm going to simulate both of my coils in three different solvers. With each different solver, I'm going to compare directly whatever results that I'm targeting. We will discuss:

• The results
• The simulation profiles
• The mesh
• Whatever is relevant to compare between these two models

We'll talk about the advantages and disadvantages of using these simplified geometries. My goal is to break these into a few short five-minute videos, and I'll be back with a more detailed video on how to do that.

Building the Geometry

Beginning with this video, we're going to build the geometry that we're going to use in the next couple of videos. We'll get right into it and start by adding in a Maxwell project. I'm going to enter the variables that I'll be using:

• Wire diameter: This corresponds to 18 gauge wire I've chosen.
• Radius of the loop
• Radius of the wire
• Number of turns

The choice of variable names will make sense next episode. I'm going to create the coil using the user-defined primitive, polygons, and the variable names. I'm going to make it a circular cross-section by entering 0 for the polygon segments. Polygon radius is where we put our wire radius. The start-helix radius will be the radius of our coil, and of course, the number of turns is the number of turns. Once this is all set, click OK.

Here I need to correct the loop radius units from centimeters to millimeters. I don't like the default coil pitch. This value just has to be greater than two times your wire radius in our case. My go-to for coils is 2.15 times the wire radius. This looks better. I'll quickly change the coil's material to copper.

Creating the Vacuum Region

At this stage, I'm going to create my vacuum region. I like to start by using the region command with the default 100% uniform padding. This makes it easy to freehand my own box on top of it, which is what I'm doing here.

The coil terminals that we set up need to be part of a closed conduction loop. In our case, we're closing the loop by entering and exiting this region. This means that we're going to need to extend the coil's leads all the way to the edge of the simulation region. I do this by orienting myself so that I'm facing one of the ends, and I make sure the grid is on the plane that I'm facing, in this case, XZ. I then draw a cylinder by clicking on the center of the face to start, selecting the edge of the wire to select the radius, and then extending the cylinder out past our cylinder. I'll do this on both sides.

Then I select the cylinder, one of the cylinders, and I click Split, and I select the split using Selected Face, and I select the face of the vacuum box. And of course, I do this on the other side too. Next, select your cylinders, make them copper, and unite them with your coil.

Finalizing the Geometry

Next, we select one of the faces, right-click on XITM, and click stuffed secondary coppe, then allow the coil to swing from one terminal to the other, via ouvert terms. Now once you're to do this, just hope your coil exists and works, and as always, use XZ to orient it according to your coil's depending on your steam operating circuit. Hit Right if you're using an XZ volt over a condenser, or auelleonte or a относster觀眾. For now, again, we'll use a single coil, which is exactly what I'm working against. Therefore it's a totally norm at the moment I'm starting my simulation right here on screen. And the next set of otheruary passages, branches is one. Right-click on both of your terminals and assign them to the winding that you created. With that, the geometry is complete.

Simplified Coil Model

Next, we'll create our coil model that uses the simplified geometry. Getting right into it, I'm going to make a copy of this design to work with. I'll reorient myself to look from the top down and create a cylinder. I'll fix the radius in a second, but here I want to be deliberate about the height of the cylinder. Once I have it at the correct height, I adjust the radius to match what I need the outer radius of the cylinder to be. I make this one the loops radius plus the wires radius.

Next, I'll select the cylinder in the model tree and make a copy of it by pressing control C then control V. Change this cylinder's radius to be the loops radius minus the wire radius. Now select your outer cylinder and then your inner cylinder in the model tree and subtract the outer cylinder and then subtract them from each other. Change the material to copper. As you can see, this cylinder looks like a pretty good geometric approximation. We can now delete our fancy coil.

Like I mentioned before, these coil terminals must be part of a closed current loop. In our other model, it was easier for me to just extend the leads to the solution boundary rather than drawing additional geometry connecting them. But in this model, it's already a closed loop, so we just need to tap into it.

To do this, select your coil under modeler surface, select section, and choose the plane you want to use for the operation. I'll choose the XZ plane here. This will create a section everywhere the object crosses this plane, which here is in two places. Keep those sections selected and right-click under edit and boolean, use the split body operation. We only need one of these, so select the one you don't like and delete it. The remaining section will be our new coil terminal. Make sure it's selected and then right-click on the excitations and add a coil terminal to it. Right-click the coil terminal and add it to your winding.

Next, we need to open up the windings properties and change this type to stranded. This will allow us to set the number of conductors in the coil terminal to our number of windings. With that complete, our simplified coil geometry is ready to go.

Conclusion

In part two, we're going to simulate and start comparing these coils. Until then, this has been Ian from Ozen Engineering. Thank you so much for watching.