Page 216 - Electric Drives and Electromechanical Systems

212 Electric Drives and Electromechanical Systems

FIG. 8.2 A single stack variable reluctance stepper motor, the flux path for winding A is shown in the radial cross
section of the motor. (A) Axial cross section. (B) Radial cross section.

sequence, with the sequence A:B:C:A:B:C . for clockwise rotation, and the sequence
A:C:B:A:C:B:A . for anticlockwise rotation. The length of a step is given by,
360
step length ¼ degrees (8.2)
N p R T
where R T is the number of rotor teeth which must be a multiple of the number of motor
phases, N p .
Fig. 8.2B shows the flux paths present when one motor winding is energised. It is
readily apparent that a small amount of flux will leak via the teeth of the unexcited poles,