Induction Motor, three phase induction motor

Slip torque characteristics of three-phase induction motor, induction motor, slip, torque,
tesla motor, Nikola tesla motor

1. TORQUE-SLIP CHARACTERISTICS OF THREE PHASE INDUCTION MOTOR Presented by Aniket Raj

2. Different Types of Electrical Motors ‹#› Electric Motors AC Motors Synchronous Induction Squirrel Cage Slip Ring DC Motors Separately Excited Self Excited Series Shunt Compound

3. INDUCTION MOTOR ‹#› Advantages of induction motor over DC motors Simple Design Simple maintenance Simple control gear for starting and speed control High efficiency low cost It can be operate in dusty and becaus the brushes are not being used. Therefore there is no possibility of sparking. No Commutator Rings single phase induction motor is not a self-starting and three phase induction motor is self-starting. Invented by NIKOLA TESLA in 1888.

4. INDUCTION MOTOR ‹#› Invented by NIKOLA TESLA in 1888. Disadvantages Of Three Phase Induction Motor Draw large starting currents, typically 6-8 x their full load values

5. Practical Applications For Induction Motors ‹#› Almost 90% Industry Machines Are Of Induction Motors. Tesla Cars (Electric Car) Electric Train Engine Grinders Elevators Lathe Machine Cooling Fans, Washing Machine ,etc.

6. ‹#› Induction Motor Components An induction motor has two main parts: A stator- The stator is the static part of the motor. The main function of the stator is to generate the rotating magnetic field. A rotor- The rotating part of the motor is known as the rotor. The rotor core and the rotor winding are the part of the rotor. stator Rotor

7. Induction Motor: Stator ‹#› The rotor is separated from the stator by a small air-gap which ranges from 0.4 mm to 4 mm, depending on the power and the size of the motor.   Three Main Parts Of Stator Stator frame : It is the outer most part of the three phase induction motor. Its main function is to support the stator, core and the winding. Stator core : The main function of the stator core is to carry alternating flux. In order to reduce the eddy current losses the stator core is laminated. Stator winding : The three phases of the winding are connected either in star or delta, when this winding is excited by three phase ac supply it produces RMF(Rotating Magnetic field).  

8. ‹#› Induction Motor: Stator Coils are placed in the slots to form a three or single phase winding. copper or aluminum wire insulated and wrapped in coils around iron cores. The 3-phase set of currents, each of equal magnitude and with a phase difference of 120°, flow in the stator windings and generate a rotating field will constant magnitude.

9. ‹#› Types Of 3-Phase Induction Motor Rotors Squirrel Cage Rotor Slip Ring Rotor or Wound Rotor

10. ‹#› The 3-phase set of currents, each of equal magnitude and with a phase difference of 120°, flow in the stator windings and generate a rotating field will constant magnitude. Stator Winding Or Field Winding Fluxes: Φ1 = Φm sin (wt) Φ2 = Φm sin (wt -120°) Φ3 = Φm sin (wt -240°) ΦT = Φ1 + Φ2 + Φ3 = 1.5 Φm So the magnitude of resultant flux is 1.5 Φm time the maximum value of flux

11. ‹#› Slots Slip Rings Carbon Brushes Conductors Slip Ring Rotor or Wound Rotor These three carbon brushes are further connected externally to a rheostat( external resistance) to have a higher resistance during starting and thus higher starting torque. . Advantages of Slip ring Rotor High Starting Torqe The rotor resistance starter can be used. Disadvantage Less Efficient Costly Complicated Construction Shaft

12. ‹#› Squirrel Cage Rotor The slots are not made parallel to each other but are bit skewed, it makes the working of motor more smooth and quieter Rotor Bars Shaft Aluminum Ring Almost 90% of the three-phase AC Induction motors are of this type. Advantages of Squirrel Cage Induction Rotor Its construction is very simple. As there are no brushes and slip ring, these motors requires less maintenance. High Efficiency Cheap Disadvantage Low starting torque Starting current high

13. PRINCIPLE OF OPERATION ‹#› An AC current is applied in the stator armature which generates a flux in the stator magnetic circuit. This flux induces an emf in the conducting bars of rotor as they are “cut” by the flux while the magnet is being moved (E = BVL (Faraday’s Law)) A current flows in the rotor circuit due to the induced emf, which in term produces a force, (F = BIL) can be changed to the torque as the output.

14. Where ‘ f s - Supply frequency P - no. of poles N s - Synchronous speed in rpm (rotating magnetic field speed) N r -(Rotor speed) The speed of the physical rotor and the speed of the rotating magnetic field in the stator must be different, If (N s = N r (Rotor speed) 🡪Rotor does not rotate (due to relatively same) (N s > N r (Rotor speed) 🡪 Rotor wants to catch the rotating magnetic pole (N s < N r (Rotor speed) 🡪 In case of induction generator Rotating magnetic field Rotor The relationship between the supply frequency, poles, and the synchronous speed (speed of rotating field), Synchronous Speed =

15. Motor never runs at synchronous speed but lower actual rotor speed The difference between synchronous speed & rotor speed is called as slip speed . If this slip speed is measured W.R.T synchronous speed, then it is called as slip (s) . Percentage slip, Speed and slip

16. If the rotor runs at synchronous speed ( N s = N R ) s = 0 (imaginary condition, At no-load the slip is nearly zero) If the rotor is stationary (N R = 0) s = 1 ( at stand still) Operation beyond the range 0 < S < 1 Speed of Rotor Frequency of rotor Relation B/W supply frequency & rotor frequency (Hz) Speed and slip

17. Speed and slip Example: If the induced emf in the stator of an 8 pole induction motor has a frequency of 50 Hz and that in the rotor is 1.5 Hz, at what speed is the motor running and what is the slip? Slon:

18. ‹#› The induction motor consists of a two magnetically connected systems namely, stator and rotor. Equivalent circuit of stator and Rotor EQUIVALENT CIRCUI T R 1 and R R : stator and rotor winding resistances X 1 and X R : stator and rotor winding leakage reactance X m : magnetizing reactance R c : core loss resistance Stator circuit Rotor circuit

19. ‹#› EQUIVALENT CICUI Combined equivalent circuit EQUIVALENT CIRCUIT Stator circuit The induction motor operates on the same principle as the transformer ,it have also two magnetically connected systems namely primary and secondary windings. (with the exception that is secondary windings are free to rotate) Rotor circuit Air gap

20. EQUIVALENT CIRCUIT Combined equivalent circuit It is easier if we can combine these two circuits in one circuit

21. ‹#› Torque The motor torque under running conditions is given by Thus for maximum torque (Tm) under running conditions : Rotor resistance/phase = Fractional slip × Standstill rotor reactance/phase Where,K 2 is a constant.

22. TORQUE-SLIP CHARACTERISTICS Case 1 : Low slip Region Assuming Slip S ≈0 (approx to zero) Where,K 3 is another constant. ( linear curve)

23. TORQUE-SLIP CHARACTERISTICS Case 1 : Low slip Region Assuming Slip S ≈0 (approx to zero) ( linear curve) Where,K 3 is another constant. Case 2 : Medium slip region Assuming Slip S=S x (General slip) ( inversely proportional to S x , hyperbolic curve) Case 3 : High slip region Assuming Slip S =1 ( at stand still )

24. TORQUE-SLIP CHARACTERISTICS Maximum Torque / Pull out torque