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Quick Electric Machines


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In the last message, I claimed motors for airliners can use magnets and copper, without superconductors. Without a new design, arguments can be scaled from my APU:

For sleek tanks and spread thrust, I propose to replace two Trent motors by six 20MW motors, as on the silhouette there
Lossy aluminum cables transport limited power only if some tanks, fuel cells sites, motors or fans are broken.

To scale the 20MW motor from the 1.27MW APU, keep the 200m/s azimuthal speed, the length and the thicknesses, multiply the gap diameter to 1.2m and the number of poles. The excellent efficiency remains, and even air cooling at the bar ends. The mass scales to 250kg without shaft nor casing. The tanks and fans are somewhat wider than 1.6m, so the motors fit. A gear doesn't look necessary.

Or each nacelle can have two D=0.6m 10MW motors, scaled from my APU, and possibly two counter-rotating fans. Same length, thicknesses, efficiency, air cooled too. Easier to integrate, may need gears.

Or accept some more mass. Increased thicknesses conduct electricity and heat better, so the copper bars can be longer and keep simple air cooling at their ends. The diameter shrinks.

Or distribute the cooling, if reliability is kept. Some alternators interrupt the magnetic circuit to let air flow radially over the copper bars. Longer bars reduce the diameter.

6MVA components and inverters exist for railway engines. I'd group the poles to use 4 inverters and avoid components in series and parallel. Instead of switching at a similar frequency a PWM for a slow motor, the inverters provide my waveforms at 2.4kHz downstream a voltage regulator
scienceforums especially scienceforums

Marc Schaefer, aka Enthalpy

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At the APU of Apr 08, 2013, I want copper to conduct the heat to the bar ends
but longer machines can't. The known answer of last message is to interrupt the iron (short for "magnetic material") to let air flow at several places. No need here to flow a coolant within the wires.


Such a design scales to any diameter and length. It circulates clean inner air among the active parts for reliability. One variant would stack a simpler shaft, spacers for air flow, and the rotor iron.

At the APU, I supposed stator iron working at 2.4kHz and peak 1.8T between the slits, but I don't have any doc for such a material. The present cooling design lets lengthen the machine for smaller induction if needed. Starting from 3*0.25t to replace a 7t Trent, even a double length would remain an excellent deal.

I still like voltage plateaus from the APU that feeds a rectifier. A motor should have the usual refinements: fractional pitch, skew and so on.

The induction could also be axial and the bars radial. Rotor and stator disks alternate then as in a turbine. The active material fits in less room, but is hard to cool and assemble. Small angles between the stator disks with one inverter each would run more smoothly.

The current fashion replaces wound synchronous motors by squirrel cages, but I believe permanent magnets make lighter machines.

Marc Schaefer, aka Enthalpy


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  • 2 months later...

"I proposed" in the first message to wrap electric motors' permanent magnets in carbon fibres...

These companies, among many more, may perhaps have come later than my message
Tesla model S plaid - Tesla recent model S - Bunting Europe - Arnold Magnetics - Eunda
but this research paper dates back to 2006, years earlier, kudos
Cho, Myeong, Choi
and meanwhile a carbon fibres sleeve gives better pre-stress than wrapped carbon fibres.

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