Superconducting Homopolar Machine With Contrarotating Rotors And Inherent Passive Magnetic Bearing

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The invention can be used as a low voltage DC-motor or as a generator for high currents. There is no clear differentiation between stator and rotor. The only quasi-stationary item is the circular formed magnetic field B created between the inner and outer ring coils 4 and 3 in the two halves of the ferromagnetic Mantelfeld-core 1 and 2. Depending on application the field coils are adapted to the inner or outer core. Both halves can rotate in opposite direction or one may stay fixed.

Mechanically fixed to the core-halves but electrically isolated from the core are the four conductive walls 5, 6, 7, 8.

Fig.1 shows shematically how the Lorentz-forces F act on the walls and Fig.2 shows how the working current flows through the machine via the brushes 9, 12, 11, 10 and 13. Opposing walls are separated by the air gap. Due to the common magnetic field the two core halves attract each other over that gap and so they work as a passive axial magnetic bearing. The core can be made out of solid steel, because no eddy currents are induced when the halves rotate. To minimize electric resistance the walls must be thick enough and when the walls are made out of ferromagnetic material like Nickel the magnetic resistance over the air gap can be limited to a minimum.

Brushes should be positioned in regions where the magnetic field is very weak (cf. Fig3).

In other drum type homopolar machines the number of brush rings is twice the number of walls. In my design four active walls (operated in contrarotating mode) need only five brush rings. That advantage can be increased when two machines are merged in one unit like it is illustrated in Fig.3. In this case eight walls require just 7 brush rings.

The best efficiency can be reached, when the coils are made of superconducting material and the coils are brought in short-circuit mode after an initial current has been introduced.

Numerous Applications will be possible:

Used as a motor in collaboration with fuel cells it can be used as direct drive for contrarotating propellers in all-electric-ships, all-electric-aircrafts, helicopters and high-power pumps. Large liquid mirrors on the moon can be driven by the machine because the machine delivers force without ripples.

Megaflywheels equipped with the machine can take advantage of the inherent axial magnetic bearing to store huge amounts of energy for several hours.

Used as a motor-generator the machine will be an effective energy source for electromagnetic launching systems on aircraft-carriers and for state-of-the-art weapons like railguns and lasers.

Used as generator for high currents with low voltage regenerative production of hydrogen by the electrolysis of water will be possible avoiding the detour over AC. The machine can be installed on windmills advantageous coupled to two contrarotating rotors whereat the produced current is directly fed to electrolyzers or transferred through superconducting cables without resistive losses over great distances.


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  • Name:
    Friedbert Schaefer
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    beginning in 1994 I wanted to invent an all-electric disc shaped VTOL-aircraft with magnetically coupled tangential rotor. the first results were too difficult to manufacture. In 2001 I finally found the solution. and when I later had read Michael Faraday’s „Experimental researches in electricity“ Vol.1 §218, I knew that my design would work
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