(a) Overcoming High Starting Current:

(i) Star-Delta Starting:

• The stator windings have end connections brought out to a starter box with six terminals.
• These are first connected in a star configuration for starting, which reduces the voltage and hence the current.
• Once the rotor comes up to speed, the windings are automatically reconfigured to delta using a timer circuit.
• Interlocks are provided to prevent both star and delta contacts from closing together, ensuring safe switching.

(ii) Auto-Transformer Starting:

• An autotransformer with tapping points is used to provide reduced voltage during starting.
• Initially, reduced voltage is supplied to the motor through the autotransformer, which lowers the starting current.
• As the rotor picks up speed, the voltage is gradually increased using higher tapping points.
• Once full voltage is reached, the mains supply is directly connected to the motor, and the autotransformer is isolated.

(b) Overcoming Low Starting Torque:

(i) Wound Rotor Motor:

• The rotor has three windings connected at one end and brought out through slip rings.
• External variable resistances are connected through brushes and slip rings.
• At starting, current passes through these resistances, producing high starting torque.
• As speed increases, the resistance is reduced and eventually short-circuited by a common connection.

(ii) Double Cage Rotor:

• The rotor is designed with two sets of bars:
  • Outer cage: small cross-section, high resistance.
  • Inner cage: large cross-section, low resistance.
• At startup, most current flows in the high-resistance outer cage, developing high starting torque.
• As the speed increases, the slip decreases, the inner cage reactance reduces, and it takes over torque production efficiently.