Join 60,000+ competitive exam aspirants
or with email
Your Cart
SubtotalтВ╣0
TotalтВ╣0
Examoogle тАв User тАв info@examoogle.com тАв EE-2024-8821
Chapter 1 of 12 тАв Page 1 of 248ЁЯФТ Protected PDF тАв Watermarked
Join 60,000+ competitive exam aspirants
In repulsion motor, the direction of rotation of the motor is determined by
the position of the brushes with respect to the magnetic field of the rotor
the position of the brushes with respect to the magnetic field of the stator
the position of the brushes with respect to the supply connection
Could be anything, we can not predict
the position of the brushes with respect to the magnetic field of the stator
Quick Trick: Remember that torque and direction in a repulsion motor depend on brush shift angle relative to the stator field axis: moving brushes clockwise or counterclockwise from the stator magnetic axis determines the direction of rotation.
Remember that torque and direction in a repulsion motor depend on brush shift angle relative to the stator field axis: moving brushes clockwise or counterclockwise from the stator magnetic axis determines the direction of rotation.
Identify the motor operating principle
A repulsion motor consists of a stator winding connected to an AC supply and a rotor armature with a commutator and short-circuited brushes.
Analyze the role of brush position
When the brush axis aligns with the stator magnetic field axis, maximum current is induced but torque is zero. When the brush axis is at 90 degrees to the stator field axis, induced voltage is zero so torque is zero. At an intermediate position (around 20-30 degrees), torque is produced.
Determine direction control mechanism
Shifting the brushes to the left or right of the stator magnetic field main axis shifts the direction of the developed torque, thereby reversing the direction of rotation.
A: Incorrect because the reference axis is the stator field, not the rotor field. C: Incorrect because changing supply connections reverses both stator and rotor fields simultaneously, keeping rotation direction unchanged. D: Incorrect because the rotation direction is completely predictable based on brush shift angle.
B is correct because shifting the brush axis relative to the stator magnetic field axis controls both torque development and direction of rotation.
In single-phase motors, remember that swapping AC line connections rarely reverses direction (like in universal or repulsion motors); direction is instead governed by brush positioning or auxiliary winding connections.