Equivalent Circuit of Single-Phase Induction Motor

 The equivalent circuit of a single-phase induction motor is similar to a transformer, but because the stator produces a pulsating magnetic field, it is represented using the double revolving field theory. The stator field is divided into forward field and backward field, each having its own rotor circuit.

1. Equivalent Circuit of Single-Phase Induction Motor

              V
              │
              │
             R1
              │
             jX1
              │
        ┌─────┴─────────┐
        │               │
   Forward Field   Backward Field
        │               │
     R2/2s           R2/2(2−s)
        │               │
      jX2/2           jX2/2
        │               │
        └───────┬───────┘
                │
               jXm
                │
               N

2. Meaning of Circuit Elements

• V = Supply voltage

• R₁ = Stator resistance

• X₁ = Stator reactance

• Xm = Magnetizing reactance

• R₂ = Rotor resistance (referred to stator)

• X₂ = Rotor reactance (referred to stator)

• s = Slip

3. Forward and Backward Field Components

• Forward field branch:
  Resistance = $R_2 / 2s$

• Backward field branch:
  Resistance = $R_2 / 2(2 - s)$

Each branch also has reactance $X_2/2$.

4. Key Idea

• The forward rotating field produces positive torque.

• The backward rotating field produces negative torque.

• Net torque = Forward torque − Backward torque.