Speed torque characteristic of a repulsion induction motor is similar to that of

Question

Examoogle · Accepted Answer

Option A: DC Series Motor

Explanation & Concepts:
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.

Working Principle: 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 ($T \propto I^2$). 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.

Key Formulas: $T \propto I^2$ — Torque relationship during starting (DC Series Motor behavior); $N \propto \frac{1}{\sqrt{T}}$ — Inverse speed-torque characteristic of repulsion phase

Key Points: 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.

Advantages: Extremely high starting torque with moderate starting current.; Smooth transition from starting to running operating mode.

Disadvantages: High initial cost due to commutator and brush assembly.; Requires higher maintenance due to mechanical centrifugal switch and brush wear.

Applications: Air compressors and refrigeration units requiring heavy starting torque.; Lifts, hoists, and machine tools.

Additional Info: 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.

Answer: 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.

Exam Tip: Remember: Any AC motor operating on the repulsion principle demonstrates DC series motor characteristics ($T \propto I^2$) during starting, making it ideal for high-inertia loads.

Examoogle · Answer

Option B: Capacitor start induction motor

Examoogle · Answer

Option C: shaded pole motor

Examoogle · Answer

Option D: Universal Motor

Correct Answer

Discussion (0)

Correct Answer

Related Questions

Discussion (0)