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
2
Electric Motors
AC Motors
Synchronous Induction
Squirrel Cage Slip Ring
DC Motors
Separately
Excited
Self Excited
Series
Shunt
Compound

3. INDUCTION MOTOR
3
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
4
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
5
✔ 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. 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
7
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

8. 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. 9
Types Of 3-Phase Induction
Motor Rotors
▪ Squirrel Cage Rotor
▪ Slip Ring Rotor or Wound Rotor

10. 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. 11
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
1. High Starting Torqe
2. The rotor resistance starter can be used.
Disadvantage
1. Less Efficient
2. Costly
3. Complicated Construction

12. 12Squirrel 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
• Almost 90% of the three-phase AC Induction motors are of
this type.
Advantages of Squirrel Cage Induction
Rotor
1. Its construction is very simple.
2. As there are no brushes and slip ring, these
motors requires less maintenance.
3. High Efficiency
4. Cheap
Disadvantage
1. Low starting torque
2. Starting current high

13. PRINCIPLE OF OPERATION
13
⮚ 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 ‘
fs - Supply frequency
P - no. of poles
Ns - Synchronous speed in rpm (rotating magnetic field speed)
Nr -(Rotor speed)
The speed of the physical rotor and the speed of the rotating magnetic
field in the stator must be different,
If (Ns = Nr (Rotor speed) ⮚Rotor does not rotate (due to relatively same)
(Ns > Nr (Rotor speed) ⮚ Rotor wants to catch the rotating magnetic
pole
(Ns< Nr (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 ( Ns = NR )
s = 0 (imaginary condition,At no-load the slip is nearly zero)
• If the rotor is stationary (NR = 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. 18
• The induction motor consists of a two magnetically connected
systems namely, stator and rotor.
Equivalent circuit of stator and Rotor
EQUIVALENT CIRCUIT
• R1 and RR : stator and rotor winding
resistances
• X1 and XR : stator and rotor winding leakage
reactance
• Xm: magnetizing reactance
• Rc : core loss resistance
Stator circuit
Rotor circuit

19. 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. 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,K2 is a
constant.

22. TORQUE-SLIP
CHARACTERISTICS
Case 1: Low slip Region
Assuming Slip S≈0 (approx to zero)
Where,K3 is another
constant.
(linear curve)

23. TORQUE-SLIP
CHARACTERISTICS
Case 1: Low slip Region
Assuming Slip S≈0 (approx to zero)
(linear curve)
Where,K3 is another
constant.
Case 2: Medium slip region
Assuming Slip S=Sx (General slip)
(inversely proportional to Sx, hyperbolic curve)
Case 3: High slip region
Assuming Slip S=1 (at stand still)

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