Contra rotating generator

#This invention, in general, relates to electrical generators. More particularly, this invention relates to a contra rotating generator apparatus for increasing relative magnetic flux speed.

#Electrical generators, in general, comprise a single rotating component called a rotor. The rotor may be either a coil wound armature or a magnetic field unit. The single rotating component of such electrical generators when designed for low rotational speeds, for example, in the range of 10 to 20 revolutions per minute, are large in physical dimensions and weight. Typically, in wind turbines, the power generated by the generator is proportional to the square of rotor blade diameter and hence there is a growing trend to build large diameter rotors, for example larger than 100 meters with each rotor blade weighing over 6 tons. The large rotor blades increase tower head weights to about 100 to 400 tons and require higher tower heights. Moreover, the fabrication of large rotor blades at wind farm sites may not be economical unless a minimum number of rotor blades are built at the same wind farm site. Furthermore, the rotor blade root-bending moment and the required wall thickness of the rotor blade increases with the square of blade length, resulting in heavier blades that further increase tower head weight. The generators with large rotor blades may therefore be difficult to transport, install, and maintain in rural or wild terrain environments.

#Although in existing contra rotating wind turbines a first rotor and a second rotor rotate in opposite direction, the magnetic field between the armature and the magnetic field unit creates a cogging torque between the first rotor and the second rotor. The cogging torque causes the second rotor of the wind turbine to rotate in the same direction as the first rotor instead of the opposite direction at low wind speeds. Moreover, due to the heavy weight of the armature, an excess amount of aerodynamic torque may be required to start the rotors rotating, Furthermore, due to small air gap between the armature and the magnetic field unit of the contra rotating wind turbines, the first rotor and the second rotor may come in contact while rotating, thereby resulting in damage of the contra rotating wind turbine.

#The foregoing summary, as well as the following detailed description of the invention, is better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, exemplary constructions of the invention are shown in the drawings. However, the invention is not limited to the specific methods and instrumentalities disclosed herein.

#FIG. 1 exemplarily illustrates a contra rotating generator assembly.

#FIG. 2 exemplarily illustrates an assembly of a cylindrical armature unit.

#FIG. 1 exemplarily illustrates a contra rotating generator assembly. The contra rotating generator 101 comprises a cylindrical armature 102 supported on an inner shaft 104. The cylindrical armature 102 comprises current carrying elements. The inner shaft 104 rotates in a first direction. A cylindrical magnetic field rotor 108 is supported on an outer shaft 105. The outer shaft 105 is oriented coaxially to the inner shaft 104. The outer shaft 105 contra rotates in a second direction opposite to the first direction. The inner shaft 104 is driven by a first prime mover 901 and the outer shaft 105 is driven by a second prime mover 902. The coaxial inner shaft 104 and the outer shaft 105 are mounted on two inner bearings. The cross-sectional view 701 of the cylindrical armature 102 and the cross-sectional view 801 of the cylindrical magnetic field rotor 108 are illustrated in FIG. 7 and FIG. 8 respectively. The cylindrical armature 102 comprises a set of first interlocking segmented stampings 401 secured by armature bolts 103. The cylindrical magnetic field rotor 108 comprises a set of second interlocking segmented stampings 501 secured by rotor bolts 109.

#Multiple cam followers 601 maintain a uniform air gap between outer surface of the cylindrical armature 102 and inner surface of the cylindrical magnetic field rotor 108. The uniform air gap prevents mechanical contact between the cylindrical armature 102 and the cylindrical magnetic field rotor 108. The magnetic field between the cylindrical armature 102 and the cylindrical magnetic field rotor 108 creates a cogging torque at low wind speeds. The cogging torque causes the inner shaft 104 and the outer shaft 105 to rotate unidirectionally. A sprag clutch 106 provided on one of the inner shaft and the outer shaft prevents unidirectional rotation of the inner shaft 104 and the outer shaft 105.

#The contra rotation between the cylindrical armature 102 and the cylindrical magnetic field rotor 108 increases relative magnetic flux speed for generating electrical power at low rotational speeds of the cylindrical magnetic field rotor 108. The relative magnetic flux speed is the sum of rotational speed of the cylindrical armature 102 and the rotational speed of the cylindrical magnetic field rotor 108. The contra rotation induces an electric current in the cylindrical armature 102. Multiple slip rings 107 transport the induced electric current to an external unit. The slip rings 107 may be of a contact type or non-contact type, for example, the emerging mercury based slip rings 107 of Mercotac®.