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Examoogle • User • info@examoogle.com • EE-2024-8821
Chapter 1 of 12 • Page 1 of 248🔒 Protected PDF • Watermarked
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In repulsion motor, maximum torque is developed when
Brush axis is at 90° electrical to the field axis
Brush axis is at 0° electrical to the field axis
Brush axis is at 45° electrical to the field axis
Brush axis is at 10° electrical to the field axis
Brush axis is at 45° electrical to the field axis
Quick Summary: In a repulsion motor, the torque is produced by the interaction between the stator field and the induced current in the rotor. The torque developed is given by $T = K I_s I_r \sin(\alpha)$, where $\alpha$ is the angle between the brush axis and the stator field axis; maximum torque is achieved at $\alpha = 45^\circ$.
In a repulsion motor, the torque is produced by the interaction between the stator field and the induced current in the rotor. The torque developed is given by T=KIsIrsin(α), where α is the angle between the brush axis and the stator field axis; maximum torque is achieved at α=45°.
T∝sin(2α) — The torque relation where α is the brush displacement angle.
T=K⋅Φs⋅Φr⋅sin(α) — Fundamental torque equation for repulsion motor.
The stator carries an AC winding and the rotor has a DC-type winding connected to a commutator. When the brushes are shifted by an angle α from the magnetic axis, the stator field induces an EMF in the rotor. The interaction between the stator flux components and the rotor armature currents creates a rotational torque that varies sinusoidally with the brush position.
At α=0° or 90°, the torque is zero because the force vectors cancel out or do not produce a net rotational component.
The repulsion motor acts as a series motor with high starting torque.
Brush position is the primary control method for speed and torque characteristics.
High starting torque
Adjustable speed characteristics
High commutator sparking
Complex maintenance compared to squirrel cage induction motors
Hoists
Textile machinery
Variable speed drives
The repulsion motor's brush shift angle α is measured relative to the stator field axis.
Option A results in zero torque as the stator and rotor fields are in quadrature.
Option B results in zero torque as there is no induced rotor current path to develop reaction torque.
C is correct — Maximum torque occurs at a brush shift of 45° electrical because the product of the flux components in the torque equation reaches its peak value at this angle.
Always remember that in commutator machines, torque is a function of the angle between magnetic axes; maximizing the projection of these axes typically yields maximum torque.