Starter in Induction Motor

Starter in Induction Motor

• Definition: A starter is a device used to safely start an induction motor by limiting the initial high inrush current and providing protection during abnormal conditions.

Why a Starter is Necessary

1. High Starting Current:

   • At starting, slip $s=1$.

   • Rotor resistance is small, so the current drawn from the supply is very high (5–7 times full-load current).

   • This can damage windings and cause voltage dips in the supply system.

2. Protection of Motor:

   • Prevents overheating of motor windings.

   • Provides overload and short-circuit protection.

3. Smooth Acceleration:

   • Ensures gradual increase in speed without mechanical jerks.

   • Protects shaft and connected equipment from sudden torque shocks.

4. System Stability:

   • Limits voltage fluctuations in the power system.

   • Prevents disturbance to other connected loads.

Common Types of Starters

• For 3-Phase Induction Motors:

  • Direct-On-Line (DOL) Starter

  • Star-Delta Starter

  • Auto-Transformer Starter

  • Rotor Resistance Starter (for slip-ring motors)

• For Single-Phase Induction Motors:

  • Resistance Starter

  • Capacitor-Start Starter

  • Capacitor-Start Capacitor-Run Starter