Power Flow Diagram and Losses in Induction Motor

Power Flow Diagram and Losses in Induction Motor

The above power flow diagram explain the input given to the induction motor ,losses occurring in induction motor & power output of motor.

As we know induction motor is electrical machine which input is electrical and output is mechanical (shaft power). Therefore losses produce in induction motor are two types:

v Constant or fix  Losses

v Variable Losses

Let us discuss induction motor losses in details:

Ø  Stator Iron or Core Loss : These losses are further divided into Eddy Current loss & Hysteresis loss. The Eddy current loss is decrease by decreasing the core lamination area which result increase the resistance & hence Eddy current loss is decreases. Hysteresis loss is minimize by using high grade of silicon sheets or core material. This losses are depend upon the frequency & supply voltage .Stator losses is also present due to flow of current in the stator winding .This losses is called copper losses or I²R loss. This is variable loss as depend upon the flow of current. In this resistance is constant and the flow of current is changing. Also there is some loss in stator core. This is constant loss. This loss is reduce by using high quality stator stamping as discuss early.

Ø Air Gap Loss : As we know that there is small air gap between motor stator & rotor. Therefore when magnetic power transfer from stator to rotor there is some loos of power due to present of air gap. This air gap loss is reduce by minimizing the air gap between rotor & stator.

Ø Rotor Losses (Rotational Loss) : These are the variable losses. This losses present in rotor due to current flow through the rotor. This losses is also call as rotor copper loss or I²R loss. 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.

Ø Stray Loss : These losses are develop due to pulsation of flux in teeth of stator and in the air gap are the main of additional losses or stray losses. These are basically by variation in load but there values cannot be determine exactly.

Ø  Friction Loss : This loss is present in induction motor due to bearing used in moto DE and NDE side. These are the constant loss. We can reduce this loss by using high quality bearing & proper time to time greasing in roller bearing. Small motor we don’t required to greasing the bearing.

Ø Windage Loss : This  loss occur in induction motor due to cooling fan, which is mounted on shaft of motor & friction between rotor & air. This is constant loss .We can minimize these loss by using proper selection of cooling fan but there is also limitation of selection of fan. If we select the wrong fan then there is chance to effect the motor cooling & result is that motor temperature increases & chance to burn the motor. Windage loss in a motor is generated by the friction between the rotor and air. The magnitude of windage loss varies widely from machine type, rotor shape and size, rotational speed, air-gap size, and rotor surface finish.