What design feature helps reduce slot ripple in a squirrel cage rotor?

What design feature helps reduce slot ripple in a squirrel cage rotor?

• A. End rings
• B. Skewed bars
• C. Parallel bars
• D. Shallow slots

Answer: (B)

Skewing the rotor bars reduces slot ripple. In a squirrel cage rotor, the conducting bars and end rings form a cage that sits in a pattern of slots around the circumference. This discrete arrangement creates a nonuniform air-gap reluctance, so as the rotor turns, the magnetic forces interact with the slots in a repeating way, causing torque pulsations known as slot ripple. If the bars are aligned straight around the rotor, these pulsations reinforce each other. Introducing a slight angle between consecutive bars (skew) shifts the magnetic interaction in angle as you move around the rotor, so the individual bar contributions are out of phase. This spreading of the torque effects cancels many of the harmonic components and smooths the overall torque, substantially reducing slot ripple. End rings connect the bars but don’t by themselves mitigate the ripple; skewing is the key design feature.

Skewing the rotor bars reduces slot ripple. In a squirrel cage rotor, the conducting bars and end rings form a cage that sits in a pattern of slots around the circumference. This discrete arrangement creates a nonuniform air-gap reluctance, so as the rotor turns, the magnetic forces interact with the slots in a repeating way, causing torque pulsations known as slot ripple. If the bars are aligned straight around the rotor, these pulsations reinforce each other. Introducing a slight angle between consecutive bars (skew) shifts the magnetic interaction in angle as you move around the rotor, so the individual bar contributions are out of phase. This spreading of the torque effects cancels many of the harmonic components and smooths the overall torque, substantially reducing slot ripple. End rings connect the bars but don’t by themselves mitigate the ripple; skewing is the key design feature.