Transit Politics Slow Down Transit Evolution, but Improving Linear Motors Could Boost It
Improving the efficiency of linear induction motors through FEMM simulations
The Canadian government has been throwing around the rumours of implementing a high-speed rail since before 1985, but they aren’t so great with the implementation part. Now, a new controversy has been brewing up about the more recent announcements of throwing the whole high-speed rail project idea into the trash and shifting over to a high-frequency train megaproject, instead worth over 5 billion dollars.
High-speed vs High-frequency: $5 Billion Fad or Timeless Transit?
High-speed rail projects began cancelling in Calgary, Ontario and throughout the country as populations in Canada were increasing and the governments were presented with shiny new plans that were more feasible and less expensive aka high-frequency rails.
Alstom, a French train equipment company, is the major company in Canada pushing towards high-speed rails and the only company in North America with a 300 kph train! While Siemens Mobility Canada is the top passenger train company in North America that is at the forefront of the push toward high-frequency trains and also happens to be German. Plus Siemens’ CEO was the former CEO of VIA Rail, which is the sole train-based, Canada-wide form of transportation and also in support of high-frequency trains.
High-frequency trains are generally designed to make more frequent starts and stops and get up and running fast, versus a high-speed train which is designed to go really fast but had a lot of technical and implementation delays.
A major part of the delays are due to Canada’s naturally “curvy” landscape which high-speed rail can only travel in relatively straight lines, leading to lots of expensive tunneling, bridging, etc. politically and economically.
Below all the government, public and train company chaos, under the train, something really cool is happening. Tiny, really tiny, negatively charged particles (electrons) are zipping through thick wires generating an electric current and causing the train to levitate.
If you remember from science/physics classes current is the electron/negative charge’s flowing rate at a specific point in a circuit.
To levitate, as electrons continue zipping through wires underneath the train they eventually reach a big metal plate and instead of moving in one direction forward or backward like in a wire, they go crazy and move in any direction they want in this metal plate.
But this metal plate is kinda special because under it it has a bunch of copper wires curved into coils. The interesting thing about coils is that when current passes through them they generate magnetic fields. This current passing through is also changing direction, it is AC (alternating current), not DC (direct current), so because the current is changing direction the magnetic fields also change direction.
It doesn’t stop with the magnetic fields, because they set off something even cooler: eddy currents.
Since under this metal plate with the coils (we call this the primary component) there is a second plate (called the secondary component) made of aluminum. And because they are close enough to each other, the magnetic fields from the top plate pass through the bottom plate and induce circular currents on its surface where the magnetic field lines enter and exit. These circular currents are called eddy currents.
As soon as these eddy currents are induced, the bottom plate zips forward due to the interaction between the magnetic fields and the newly induced eddy currents. That is how the high-speed train and the high-frequency train could move forward, it uses a linear induction motor (LIM) which is ideal for heavy-duty applications like high speed and frequent stops and starts. You can read more about LIM applications with hyperloops below:
Often these motors are very inefficient for multiple reasons that are discussed in the article above.
LIMs Are Energy Inefficient for 4 Reasons:
- Air gap: If the gap between the primary and secondary components is big, magnetic fields have to travel longer from top to bottom which gives more opportunity for lost energy. (more in the article above!)
- DC power losses: Copper loses as current moves through the coils and creates waste heat.
- AC power losses: When there is an uneven distribution of alternating current more current near the surface/outer layers of the conductor and less current toward the center.
- Core material losses: The wrong material can lead to core losses which is wasted heat from eddy currents and hysteresis
DC Power Losses: Electrical Resistance
DC (direct current) power losses are essentially any energy that is lost in components that use DC like the copper coils.
When current passes through any material energy loss is inevitable because all materials have resistance unless a few special ones are called superconductors that are not practical to use. Read my superconductor article to learn more!
AC Power Losses: End Effects
AC (Alternating current) power losses happen when energy is lost with components that use alternating current, so current that changes direction. A major contributing factor to AC power losses is the End Effects which are a group of weird effects that happen at the ends of linear motors.
One of the most common is the Skin Effect, where there is a collection of excess AC towards the surfaces or “skin” of a motor instead of being evenly distributed throughout creating a lot of extra heat towards the edges. Skin effect is usually managed with larger wire. This increases the space for AC to flow since a larger area leads to less resistance. But we still need to consider that thicker wire cannot create a coil with as many turns and take up more space than a coil with a thinner wire which, so there is a trade-off here between efficiency and space constraints.
Litz wire is also fairly common where wire strands are coated with an insulator, woven together, and carry current. This way the total surface area for more current to flow is larger and so it reduces the skin effect too.
Some even used hollow metal rods instead of regular metal wires for radio-frequency (RF) and antennas since AC wouldn’t flow through the centre!
Core Materials Losses: Uncontrolled Currents
Unsurprisingly energy losses, as heat, can happen at the core/secondary component too. There are 2 main reasons for it: eddy currents and hysteresis.
So, the ideal secondary material has low hysteresis and few eddy currents. We know that when current runs through a conductor, it will encounter resistance which creates heat, and this applies to eddy currents too. To reduce how much heat is lost we create layers of insulating material in the secondary component where the eddy currents are produced. This is called laminating a metal and it reduces how much area is available for the eddy currents to flow through which reduces the current, but also reduces how much the current is moving. If you put too much insulating material, reducing the eddy currents too much, there won’t be enough to interact with the magnetic fields and the LIM will have less thrust. It is key to optimize for a balance which can vary depending on the LIMs’ specifications.
Hysteresis is the lag from how fast the magnetic secondary responds to changing magnetic fields leading to energy losses. So if a magnetic field is introduced and the secondary doesn’t immediately become magnetized same as removing a magnetic field, this lag is hysteresis. If this happens repeatedly there will be energy lost as heat that makes up a huge portion of overall low efficiency.
In summary: The ideal core material:
- Low hysteresis loops
- Low eddy current losses
- High magnetic permeability: easily conducts and intensifies magnetic fields generated
Common core materials are laminated steel, and ferrite materials (like iron).
How to Build a Motor
1. What/Why/Who are you making this for?: Identify weak points & specifications
Before you build anything it’s a good idea to think about why you are doing it in the first place. Is it for work, for fun?
It’s also really important to be clear on what the motor is for because first of all there are 50+ different kinds of motors, and each of them is used for different things.
I’m working on linear induction motors (LIMs), so for my LIM because this was a preliminary model I made it small:
Primary component:
- 16 cm in length
- 6 cm in width
- 0.6 cm in height or 1.6 cm for the portions including the notch to wrap around a coil
Secondary component:
- 1 cm in length
- 6 cm in width
- 1.3 cm in height
2. What will it look like?: Make a concept drawing
It’s better to fail on paper, before losing hours failing on a computer. So, once I decided on the specifications for my motor, I drew it out and then built it in a 3D software. For many engineering tasks, SolidWorks is the industry standard so I used that to create a basic model of what my LIM would look like.
3. Draw, simulate, test, fail, iterate, repeat: FEMM
After you have a good idea of what the motor will look like, it’s time to simulate it to see if it will really work.
To simulate motors the industry standard is FEMM (Finite Element Method Magnetics). FEMM is a platform that allows users to see the magnetic field lines that form in various types of motors through a cross-sectional view.
For my LIM, I simulated just the primary component and used steel M50, which is very strong and heat resistant making it good for high-stress uses.
For the copper coils, I used 10 AWG (American Wire Gauge — refers to thickness) copper winding which means that the copper I used is fairly thick so it’s more capable of carrying higher currents than the larger numbers like 15 and 20 gauge. Since a larger gauge value corresponds to smaller wire diameters.
Simulating your motors takes your concept designs to the next level, they let you test and iterate motor designs with greater accuracy before even having to spend the time and money building it just to have to test and iterate all over again saving time, money and resources due to small problems you could have caught in a simulation. Plus by simulating motors before building users can better understand the behaviours of their motors, and how they would function, providing more insights into how to optimize electric motors for their specific uses. Overall you get more efficient, less expensive and shorter development times for electric motors.
4. Build it — I’m not there yet
After drawing, 3D building, and simulating a few times you’re probably ready to start building! I’m not there yet, I’m still in the simulating stage. So part 2 of this project will be the math of it.
Going forward I am going to get into the mathematics of how LIMs work to make a more complex simulation and get a more in-depth understanding of LIMs. I am going to continue using FEMM for magnetic simulations, but I’ll also be using Ansys (Analysis Software) which is another simulation software except it works in 3D whereas FEMM only works in 2D.
Thanks for reading
I hope you were inspired by the future of what we can do with more efficient high-speed motors, and a little entertained by the transportation politics!
Hey! I’m Julia, thanks so much for reading my article, if you enjoyed it add a clap and follow on Medium for more on green energy and transportation.
Right now, I’m curious about exploring energy & transportation solutions, synthetic biology, and nanotech’s role in it all. For more from me, you can connect with me on LinkedIn and subscribe to my monthly newsletter!
