Novel wire, cooled from inside, doubles power density
Electric motors are increasingly moving into high-power, high-performance applications, such as cars and aeroplanes. A limiting factor in the use of electric motors for vehicles is their power density. For now, this remains uncompetitive with fuel engines. Power density means the amount of power produced from a given volume of engine space. A steam locomotive has low power density, because it produces little power relative to its huge volume. Whereas, a race car engine has extremely high-power density, producing tremendous power from a small space. Power density for electric motors crucially depends on temperature. Electricity moving through a wire creates heat. Increasing the current increases the power density, but that also means more heat. At a certain point, wires will burn out. To prevent fires, electrical devices include safety cut-offs. The temperature that wires can take also limits potential power density. Cooling the wires would help significantly, but this is very difficult to achieve in practice. Wires are electrically insulated, which also makes them virtually impossible to cool externally.
Cooled from inside
The EU-funded Capcooltech project solved this problem with a new type of wire. The wire is hollow, with a cooling liquid pumped through it. The project developed and marketed the new wiring technology, initially for automotive applications. Coils – literally, coils of wire wrapped around a metal core – are an important component of electric motors. “By using hollow wires, which are wound to coils,” explains project coordinator Michael Naderer, “we can cool the coils at the hottest points, directly in the copper.” Researchers also developed special connectors that join fluid-filled wires to the coils. The team investigated optimal winding and connection configurations.
Increased power density and performance
The cooling permits an increased current, and this leads to a proportional increase of the power density. So far, the team has doubled the normal power output. This achieves a performance improvement of nearly double, too. Increased power density means more power for less weight. And since this is exactly what the electric aviation and automotive industries strive to achieve, the Capcooltech developments are of great interest to these industries. The automobile industry will be able to produce cheaper, more efficient and more powerful motors. “In practical terms,” adds Naderer, “you will be able to drive an electric car, towing a trailer, up a mountain without the car breaking. The aeronautical industry will build electric taxis, and drones which can carry heavier payloads for longer.” Capcooltech’s technology will also allow the manufacturing industry to increase productivity via faster and more efficient machines. Project researchers had hoped to target the automotive 48-volt market. This is likely to be the new standard for future electric cars and projected to be worth billions of euro in coming years. The team has not yet broken into this market. The COVID-19 pandemic also upset other project plans. The team adapted, and is now seeking alternative markets. The new plan is to be in full production by 2024.
Keywords
Capcooltech, electric, motors, wires, cooling, power, power density
