Patent ID: 7500531

Claim:
A top drive drilling system using a low speed AC motor, comprising: a motor frame, a low speed AC motor including: a stator assembly affixed to the motor frame and comprising a plurality of stator laminates compressed into a stator core; a spider comprising a hollow tube having a plurality of ribs located on the outer tube surface and oriented such that the length of the ribs are coincident the length of the hollow tube, wherein each of the plurality of ribs has an outer radial surface; a rotor core comprising a plurality of compressed rotor laminates affixed to the outer radial surface of the spider ribs; a hollow motor shaft to which the spider is coupled; first and second bearing assemblies mounted between the motor frame and the hollow motor shaft such that the rotor core may rotate relative to the stator assembly; and a motor drive for generating a variable frequency pulse-width modulation signal to drive the AC motor at speeds of about 0 to 300 rpm thereby avoiding speed reduction equipment.