Why double squirrel cage motor used in barring gear? Why?

1.	Why double squirrel cage motor used in barring gear? Why?
Answer» To have high starting torque. In AC motors torque is directly proportional to φ (flux), I₂ and cosφ₂. i.e T ;φ (flux* I₂ * cos φ₂. ∴ T = k * φ (flux)* I₂ * cos φ₂. Rotor at standstill E₂;φ (flux) ∴ T = k * E2 * I₂ * cos φ₂. In double squirrel cage motor inner cage is low resistive and high inductive. The outer cage is high resistive and low inductive. In case of inner cage Z (impedance) is less (X_L = 2π f L). If the rotor is having high inductance at starting I2 will lag E2 by large and cos φ₂ (Rotor PF = R₂ / Z₂) is very less. So torque is less. At staring rotor torque is proportional to the rotor resistance. At starting inductance is high and the Z is

Answer»

To have high starting torque.

In AC motors torque is directly proportional to φ (flux), I₂ and cosφ₂.

i.e T ;φ (flux* I₂ * cos φ₂.

∴ T = k * φ (flux)* I₂ * cos φ₂.

Rotor at standstill E₂;φ (flux)

∴ T = k * E2 * I₂ * cos φ₂.

In double squirrel cage motor inner cage is low resistive and high inductive. The outer cage is high resistive and low inductive. In case of inner cage Z (impedance) is less (X_L = 2π f L). If the rotor is having high inductance at starting I2 will lag E2 by large and cos φ₂ (Rotor PF = R₂ / Z₂) is very less. So torque is less.

At staring rotor torque is proportional to the rotor resistance. At starting inductance is high and the Z is

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