# Power Flow Diagram and Losses of Induction Motor

**Power Flow Diagram** of Induction Motor explains the input given to the motor, the losses occurring and the output of the motor. The input power given to an Induction motor is in the form of three-phase voltage and currents.

The Power Flow Diagram of an Induction Motor is shown below.

The power flow is is given by the equation shown below.

Where, cosϕ_{i} is the input power factor

The **losses** in the stator are

**I ^{2}R** losses in the stator winding resistances. It is also known as

**Stator copper losses**.

**Hysteresis** and **Eddy current** losses in the stator core. These are known as **Stator core losses**.

The output power of the stator is given as

This output power of the stator is transferred to the rotor of the machine across the air gap between the stator and the rotor. It is called the **air gap Pg** of the machine.

Thus,

The Power output of the stator = air gap power = input power to the rotor

The losses in the rotor are as follows.

I^{2}R losses in the rotor resistance. They are also called** Rotor copper losses** and represented as

Hysteresis and eddy current losses in the rotor core. They are known as** Rotor core** **losses**.

**Friction and Windage losses P _{fw}**

**Stray load losses** P_{misc}, consisting of all losses not covered above, such as losses due to harmonic fields.

If the rotor copper losses are subtracted from rotor input power P_{g}, the remaining power is converted from electrical to mechanical form. This is called **Developed Mechanical** **Power P _{md}.**

Developed Mechanical power = Rotor input – Rotor copper loss

The output of the motor is given by the equation shown below.

P_{o} is called the **shaft power** or the **useful power.**

### Rotational losses

At starting and during acceleration, the rotor core losses are high. With the increase in the speed of the induction motor these losses decreases. The friction and windage losses are zero at the start. As the speed increases the losses, also start increasing. The sum of the friction, windage and core losses are almost constant with the change in speed. These all losses are added together and are known as **Rotational Losses**.

It is given by the equation shown below.

The** Rotational losses** are not represented by any element of the equivalent circuit as they are purely mechanical quantity.