Losses in 3 phase induction motor

Losses in 3 phase induction motor

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, P in   = √3 V L I L Cos φ

12. Power Transfer Stages of Induction Motor Where  V L  and I L  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, P 2   So,     P 2   =  P in  -  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 ' P 2  ', we get the gross mechanical power developed by the motor, P m       P m   =  P 2  -  Rotor Copper losses A part of  ' P m  '  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, P out

14. Efficiency of an Induction Motor The ratio of net power available at the shaft ( P out  ) and the net electrical power input (  P in  ) to the motor is called as overall Efficiency of an Induction Motor.  % Efficiency  =  ( P out / P in ) × 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/efficiency-and-power-flow-diagram-of-induction-motor.html

18. Thank you