There are two types of losses that occur in three-phase induction motors: fixed losses and variable losses. Fixed losses such as iron/core losses, mechanical losses, and brush friction losses remain relatively constant, while variable or copper losses change with load. Iron/core losses are minimized through lamination and use of high-grade silicon steel. Mechanical losses occur at bearings and brush friction only in wound rotor motors. Variable losses occur due to current in stator and rotor windings and change with load. Power is transferred through various stages in an induction motor from electrical input to mechanical output. Efficiency is the ratio of output power to input power.

1. Directorate of Technical
Education,
Tamilnadu.
Thanthai Periyar Government
Institute of Technology,
Vellore–632002
Department of ECE

2. Losses in 3 phase induction
motor
Unit 4
Presented by
M.P.Sasirekha

3. Losses in 3 phase induction motor
• There are two types of losses occur in three
phase induction motor.
• These losses are,
• Constant or fixed losses,
• Variable losses.

4. Constant or Fixed Losses
• Constant losses are those losses which are
considered to remain constant over normal
working range of induction motor. The fixed
losses can be easily obtained by performing no-
load test on the three phase induction motor.
• These losses are further classified as-
• Iron or core losses,
• Mechanical losses,
• Brush friction losses.

5. Iron or Core Losses
• Iron or core losses are further divided into
hysteresis and eddy current losses. Eddy current
losses are minimized by using lamination on core.
• Since by laminating the core, area decreases and
hence resistance increases, which results in
decrease in eddy currents. Hysteresis losses are
minimized by using high grade silicon steel.
• The core losses depend upon frequency of the
supply voltage.

6. Iron or Core Losses
• The frequency of stator is always supply
frequency, f and the frequency of rotor is slip
times the supply frequency, (sf) which is always
less than the stator frequency.
• For stator frequency of 50 Hz, rotor frequency is
about 1.5 Hz because under normal running
condition slip is of the order of 3 %. Hence the
rotor core loss is very small as compared to stator
core loss and is usually neglected in running
conditions.

7. Mechanical and Brush Friction Losses
• Mechanical losses occur at the bearing and
brush friction loss occurs in wound rotor
induction motor.
• These losses are zero at start and with
increase in speed these losses increases. In
three phase induction motor the speed
usually remains constant. Hence these losses
almost remains constant.

8. Variable Losses

9. Variable Losses
• These losses are also called copper losses. These
losses occur due to current flowing in stator and
rotor windings.
• As the load changes, the current flowing in rotor
and stator winding also changes and hence these
losses also changes.
• Therefore these losses are called variable losses.
The copper losses are obtained by performing
blocked rotor test on three phase induction
motor.

10. Power Transfer Stages of Induction
Motor

11. Power Transfer Stages of Induction
Motor
• Induction motor converts an electrical power
supplied to it into mechanical power. The
various stages in this conversion is called as
power transfer stages in an induction motor.
• The 3-phase power input to an induction
motor i.e,
• Stator input,
• Pin = √3 VL IL Cos φ

12. Power Transfer Stages of Induction
Motor
• Where VL and IL are the line values of stator
supply voltage and current and Cos φ is the
power factor of the motor.
• A part of this power is consumed in stator
iron and copper losses. The remaining power
is transferred inductively to the rotor through
the air-gap. This is called as Rotor Input, P2
• So,
• P2 = Pin - Stator iron and Copper losses

13. Power Transfer Stages of Induction
Motor
• The rotor losses are dominantly copper losses as
rotor iron losses are very small and hence
generally neglected.
• By substracting the rotor copper losses from
' P2 ', we get the gross mechanical power
developed by the motor, Pm
• Pm = P2 - Rotor Copper losses
• A part of ' Pm ' is consumed as mechanical losses
and the remaining is the power available to the
load at the shaft. This is called as Net Output
Power of the Motor, Pout

14. Efficiency of an Induction Motor
• The ratio of net power available at the shaft
( Pout ) and the net electrical power input
( Pin ) to the motor is called as overall
Efficiency of an Induction Motor.
• % Efficiency = ( Pout / Pin ) × 100

15. Efficiency of an Induction Motor

16. Efficiency of an Induction Motor
• Rotor Efficiency,

17. Reference
• https://www.electrical4u.com/losses-and-
efficiency-of-induction-motor/
• https://www.electricaldeck.com/2020/04/effi
ciency-and-power-flow-diagram-of-induction-
motor.html

18. Thank you