In any electrical machine losses are the most important factor to be considered. They help us to determine the efficiency and performance of any electrical machine.
In similar context, losses in induction motor are the important factor to determine the efficiency of induction motor.
To understand the losses of a three phase induction motor, first of all we have to understand the process of conversion of electrical energy into mechanical energy. We have discussed this process in detail in the working of three phase induction motor.
An induction motor converts
electrical energy into mechanical energy. During this process of
electromechanical energy conversion some part of input power is lost in the
form of Electrical Losses and Mechanical Losses in different
parts of the induction motor.
Electrical losses in Induction Motor
As the name implies, electrical
losses are the loss of electric power in copper windings and in the core of
stator as well as rotor. There are two types of electrical losses in induction
motor
- Copper loses
- Core loses
Copper loses
As the name implies, Copper
losses are the loss of power in copper windings of stator and rotor. These
losses are due to the electrical resistance offered by the windings to the
electrical current flowing through it.
Core loses
Core losses are the loss of
magnetic flux in the magnetic core during the electromechanical and energy
conversion.
Core losses are for the divided
into Eddy current Losses and Hysteresis Losses. These two types of losses are due
to the high frequency harmonic current and depend on the frequency supply
voltage.
Mechanical Losses in Induction Motor
Mechanical losses are the loss
of power in different mechanical parts of the induction motor due to friction
and other physical obstructions. These losses are further divided into Friction
Losses and Windage Losses.
Friction losses in induction motor are caused by the friction between different mechanical parts like shaft, bearing and brushes.
Windage Losses in induction motor occur due to the aerodynamic pressure on the rotating part of the motor.
Power Stages in Induction Motor
To ease the study of
electromechanical energy conversion the stages of electrical the power flow in
induction motor is bifurcated as follows.
PScu =
Stator Copper Losses
PSco =
Core Losses
Stator Power Output (PS,O/p) = Pi - (PScu + PSco)
Stator Power Output (PS,O/p)
= Rotor Power Input (PR,i/p) = Air gap
power (Pag)
PRcu =
Rotor Copper Losses
PRco =
Rotor Core Losses
Shaft input power (PSh,i/p) = Rotor Power Ouput (PR,o/p) = PR,i/p
- (PRcu + PRco))
PR,o/p = PSh,i/p =
ω = 2.π.N / 60
Tg =
Gross torque developed in the induction motor
ω = Angular
frequency of the rotor
During the development of gross torque in induction motor some power is lost in mechanical parts of the induction motor due to the friction and aerodynamic pressure. Let us say
Pmech = Mechanical losses
Pf = Frictional Losses
Pw = Windage
Loses
Pmech = Pf + Pw
After these losses the net power transferred to the shaft output is responsible for the net torque development in induction motor and this is the actual output power of the induction motor.
Net Power Output (Pnet,o/p)
= PSh,i/p - Pmech
Constant losses in Induction
Motor
It is discussed earlier that in
stator core losses and copper losses occur. As the core losses are frequency
dependent and the supply frequency is constant so the stator core losses are
categorized as constant losses. And the rotor core losses are neglected because
during the operation of induction motor slip is very low and the frequency
supplied to the rotor is slip dependent hence the frequency supplied to the
rotor is very low.
Variable losses in Induction
Motor
The stator copper loss, rotor
copper loss and the mechanical losses are load dependent; they varies according
to the load. So they combinedly categorized as variable losses.
No comments:
Post a Comment
Please feel free to provide feedback and suggestions, and also don't hesitate to ask your questions.