The U.S. Department of Energy’s Advanced Research Projects Agency-Energy (ARPA-E) recently announced the release of funding to several organizations working on electric aircraft, including General Electric, as part of its Connecting Aviation By Lighter Electric Systems (CABLES) program.
“Future all-electric, twin-aisle aircraft will require more than 50 MWs of power distribution capability,” the agency said in a blog post last year. “Therefore, the targeted outcome of this topic is to enable megawatt scale distribution with minimal impact on weight while maintaining the high reliability and safety requirements of aviation.”
At the end of last month, GE tweeted, letting everyone know that the project is now moving forward.
GE engineers are performing 🎩“MAAGIC”🎩 with @ARPAE to help enable #electric flight. Read the agency’s blog to learn more about our exciting new project. https://t.co/3Z7mFpPYFK – click on the topic "Connecting Aviation By Lighter Electric Systems (CABLES)" @GEAviation pic.twitter.com/Jw6f9Zu7uU
— GE Research (@GEResearch) February 26, 2021
Funded Projects
The idea behind all of these projects is to build a cabling system that can handle the loads needed by a future electric aircraft without being too big, heavy, and bulky to be effective in the air. If you have a great electric motor, great batteries, but no lightweight way of getting the power from one to the other, you’re still grounded.
GE’s approach to this is called Megawatt Any-Altitude Gas Insulated Cable system for aircraft power distribution (aka MAAGIC). The plan is to use carbon dioxide gas to insulate and cool the power cables. The technology, once ready for production, will be useful for other types of electric craft on the ground and in the ocean as well. Additionally, it will be useful for offshore wind turbines. The total funding for this was just under $3.5 million.
The Illinois Institute of Technology will be working on circuit breakers that can handle the same stresses as GE’s gas-insulated cables. According to ARPA-E, the advanced breaker technology “conducts a DC load current through a high-temperature superconducting winding of a pulse transformer. Under a fault condition, the SMCI injects a high transient voltage via the transformer, drives the fault current to zero quickly, and holds the current as a small AC ripple current, allowing the mechanical switch to open safely and isolate the fault.” Funding for this is just over $750,000
Virginia Tech’s approach is called EPS, possibly a nod to Star Trek. In this case, though, EPS stands for Electric Power System (sorry, no plasma conduits, but that means no exploding consoles or flying rocks, so that’s a plus). According to ARPA-E, the system’s innovations include “conductors with increased current-carrying capacity; a multilayer, multifunctional insulation system made of exceptionally high thermal conductivity materials; and a new insulation solution for higher voltages with superior mechanical strength and electrical reliability.” Funding for this was just under $1.2 million.
The University of Tennessee is working on solid-state circuit breakers for aircraft. “The team will develop a modular architecture with a highly integrated customized module, use advanced solid-state semiconductor devices cooled at cryogenic temperatures, and integrate protection intelligence to achieve project objectives.” Funding for this is $1.4 million.
Advanced Conductor Technologies LLC of Boulder, Colorado, is working on cables that don’t need breakers. “The cables and connectors will contain insulation independent of the cryogenic medium used as coolant and allow an operating voltage of 10 kV. Because they have intrinsic fault current limiting capabilities, the cables can protect the power distribution network from over-currents. This intrinsic capability will reduce the complexity of the power distribution network while improving its reliability.” If this works out, they’ll save a lot of weight and bulk for aircraft. Funding for this was $1.4 million.
Hyper Tech Research, Inc of Columbus, Ohio, will be working on cables cooled by liquefied natural gas. Cooled to around 120 degrees kelvin (-153°C, -243°F), this low temperature helps the cables move lots of current at high voltages without needing to be large and bulky. The insulating gases can be recycled into propulsion systems or burned in an onboard generator. Funding for this was about $1.6 million.
Why These Projects Matter
Electric aviation, especially for large passenger and cargo aircraft, is going to require a lot of electricity. The power density of batteries is rapidly improving, so eventually it will be possible to power large aircraft with batteries. That kind of power, if using normal cables, would make for a lot of the space and weight capacity of the plane being used on cables. I don’t think anyone needs to explain why that would be problematic.
It’s good to see ARPA-E funding different approaches to making smaller, lighter cables that can handle those kinds of loads. If one doesn’t work out, one of the others might. Also, having multiple successful approaches will make for a stronger industry that doesn’t become too dependent on one type of technology. Going forward, it also helps future improvements to grow past dead-ends instead of allowing the electric aircraft cabling industry to get stuck in “local maximums” as Elon Musk would say.
Star Trek jokes about exploding consoles aside, it can actually be quite dangerous to move that kind of energy around. If something goes wrong, that isn’t just a minor electrical fire. You could end up with serious deadly problems if something carrying that much current shorts out. The arcing alone would be much more powerful than a welder. Getting this right and safe will take time, and it’s good to get a head start on it.
This is especially true considering the exotic and complicated power delivery systems the different organizations are proposing. If the gas insulation and/or coolant leaks or ignites, the sudden inability of the wiring to handle the loads is a frightening prospect. Early versions of these technologies will probably be expensive, fragile, and prone to failures. We definitely need to get past those issues and get toward reliable, mature technologies if we are going to trust them in aircraft.
Finally, as GE pointed out, the technologies for this won’t only be useful in the skies. Marine applications, large ground craft, and submarines will all benefit from this technology. Like aircraft, many other types of vehicles will need serious power but won’t have the room for giant cables to move that power around. The benefits of these power distribution technologies will likely become useful outside of transportation as well. It will be a great thing to see as many of them as possible succeed.
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