Line start permanent magnet motor using a hybrid rotor
A rotor system for a downhole motor comprises a set of permanent magnets, a set of conductors and a pair of end conductor rings connecting the set of conductors. The set of permanent magnets and the set of conductors being substantially coaxial and having the substantially the same linear extent. The set of permanent magnets can be located radially inwards from the set of conductors, and may be provided by discrete conductive bars.
1. A rotor system for a downhole motor comprising:
a set of permanent magnets;
a set of conductors comprising discrete conductive bars; and
a pair of end conductor rings connecting the set of conductors;
the set of permanent magnets and the set of conductors being substantially coaxial and having the substantially the same linear extent;
the set of permanent magnets and the set of conductors both being set in a rotor body, the rotor body having an outermost outer surface, the outermost outer surface featuring notches in which the conductors are set; and
a conductive material substantially formed around a cylinder, the thickness of the conductive material varying around the radius of the cylinder in an alternating manner, so as to provide relatively thick portions that are generally axially aligned.
2. A rotor system according to claim 1 wherein the set of permanent magnets are located radially inwards from the set of conductors.
3. A rotor system according claim 2 wherein the permanent magnets are set in axial cavities formed inside the rotor body.
4. A rotor system according to claim 1 wherein the discrete conductive bars are set in curved axial notches formed on the outermost outer surface of a rotor body.
5. A rotor system according to claim I wherein the conductive bars are set in notches having a dovetailed section formed on the outermost outer surface of a rotor body.
6. A rotor system according to claim 1 wherein the permanent magnets are set in notches having a dovetailed section formed on the outermost outer surface of a rotor body.
7. A rotor system according to claim 1 wherein a through bore is included.
8. A plurality of rotors according to claim 1 , joined in series by a connection.
9. A plurality of rotors according to claim 8 wherein the connection comprises a male self lock taper on one rotor, and a corresponding female self lock taper on the other rotor.
10. A rotor system according to claim 8 wherein the connection includes a spline or key capable of transferring torque between rotors.