Question

a) Briefly describe TWO (2) types of stepper motor that are commonly used.

b) A linear induction motor drives a conveyor belt at speed of 50 km/h with a slip of 20% at 50 Hz and developed a thrust of 300 N. Determine:

i) Pole pitch of the motor.

ii) Power developed by the motor.

iii) Copper loss in the secondary side.

iv) The new value of synchronous speed if pole pitch is increase to 0.5 m.

Answer 1

a)

A stepping motor is fed through an external drive circuit which receives input voltage pulses and delivers appropriate currents to the stator windings of the motor.

There are two type of Stepper motors that are commonly used:

1. VARIABLE RELUCTANCE STEPPING MOTOR

2.PERMANENT MAGNET STEPPING MOTOR

BRIEF DESCRIPTION:

1. VARIABLE RELUCTANCE STEPPING Motor(VRSM)

These motors have salient pole stator with concentrated three or four phase windings and a salient pole rotor. The rotor doesn't have any windings and it is made from ferromagnetic s laminations.

The stator produces a flux which rotates the rotor through a single step, so that the reluctance seen by the stator field is minimum and the stator flux linkages are maximized for given stator currents. Lower values of step angle can be achieved by using a stepping motor with more number of poles on stator and teeth on rotor.

2. Permanent Magnet Stepping Motors(PMSM)

The stator of a PMSM do also have salient poles with concentrated windings just as in VRSM. The rotor in these motors, as the name suggests, have permanent magnet poles. In PMSM , some torque is produced which aligns the rotor poles with the stator teeth, which is not in the case of VRSM, however PMSMs are not feasible to have smaller steps.