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In repulsion motor, If the brushes are shifted clockwise from the main magnetic axis, the motor will _______________ .
rotate in an anticlockwise direction.
rotate in a clockwise direction.
remain unchanged (direction does not depend on brushes shifting)
stop
rotate in a clockwise direction.
Quick Trick: A repulsion motor always rotates in the direction of the brush shift from the main magnetic axis (alpha = 0 degree axis). Shift clockwise to rotate clockwise, and shift anticlockwise to rotate anticlockwise.
A repulsion motor always rotates in the direction of the brush shift from the main magnetic axis (alpha = 0 degree axis). Shift clockwise to rotate clockwise, and shift anticlockwise to rotate anticlockwise.
Identify Stator and Brush Axis Relationship
In a repulsion motor, torque is generated due to the interaction between the stator magnetic field axis and the rotor magnetic axis determined by the short-circuited brush axis.
Determine Torque Direction from Brush Shift
When brushes are aligned with the stator field axis (alpha = 0 deg), torque is zero. Shifting the brushes creates a displaced magnetic pole on the rotor. The mechanical torque developed acts to reduce the magnetic reluctance, driving the rotor in the exact direction of the brush shift.
Apply Clockwise Shift Condition
Since the brushes are shifted in a clockwise direction, the resulting electromagnetic torque will also act in the clockwise direction, making the motor rotate clockwise.
A: Shifting clockwise causes clockwise rotation, not anticlockwise. C: Direction depends directly on the direction of brush shift. D: The motor does not stop; it rotates smoothly in the shifted direction.
B is correct because a repulsion motor always rotates in the same direction in which the brushes are shifted relative to the main stator field axis.
Remember that shifting brushes to the left (anticlockwise) gives anticlockwise rotation, while shifting right (clockwise) gives clockwise rotation; if brushes are at 0 or 90 electrical degrees, zero torque is developed.