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Speed torque characteristic of a repulsion induction motor is similar to that of
A) DC Series Motor
B) Capacitor start induction motor
C) shaded pole motor
D) Universal Motor
DC Series Motor
A repulsion-induction motor combines the high starting torque of a repulsion motor with the constant-speed characteristics of an induction motor. During the starting phase, it operates purely on the repulsion principle, producing a high starting torque and a inverse speed-torque relationship characteristic of a DC series motor.
A repulsion-induction motor combines the high starting torque of a repulsion motor with the constant-speed characteristics of an induction motor. During the starting phase, it operates purely on the repulsion principle, producing a high starting torque and a inverse speed-torque relationship characteristic of a DC series motor.
T∝I2 — Torque relationship during starting (DC Series Motor behavior)
N∝T1 — Inverse speed-torque characteristic of repulsion phase
At starting, the short-circuited brushes are positioned on the commutator, setting up a strong repulsion torque similar to a DC series motor where torque is proportional to the square of current (T∝I2). As the rotor accelerates to about 75% of synchronous speed, a centrifugal mechanism short-circuits the commutator bars to form a squirrel-cage winding, transitioning the operation to a constant-speed induction motor.
High starting torque, typically 300% to 400% of full-load torque.
Starting current is relatively low compared to standard single-phase induction motors.
Behaves like a DC Series motor at starting and during the repulsion operation phase.
Extremely high starting torque with moderate starting current.
Smooth transition from starting to running operating mode.
High initial cost due to commutator and brush assembly.
Requires higher maintenance due to mechanical centrifugal switch and brush wear.
Air compressors and refrigeration units requiring heavy starting torque.
Lifts, hoists, and machine tools.
Option B (Capacitor start induction motor) provides high starting torque but exhibits standard induction motor speed torque characteristics.
Option C (Shaded pole motor) has very low starting torque and low efficiency.
Option D (Universal motor) can run on both AC and DC, but a repulsion induction motor specifically employs induction motor action at running speed.
A is correct — The repulsion induction motor exhibits a hyperbola-like speed-torque characteristic during starting, which directly mimics the characteristic of a DC series motor.
Remember: Any AC motor operating on the repulsion principle demonstrates DC series motor characteristics (T∝I2) during starting, making it ideal for high-inertia loads.