1. ELECTRICAL MACHINES – I
Presented by
CH. BHARATHI
Assoc. Professor
DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING
VISAKHA INSTITUTE OF ENGINEERING & TECHNOLOGY

2. Hans Christian Oersted (1777 – 1851)X
1822
In 1820 he showed that a current produces a magnetic field.

3. André-Marie Ampère (1775 – 1836)
French mathematics professor who only a week after learning of Oersted’s discoveries in Sept demonstrated that parallel wires carrying currents attract and repel each other.
attract
A moving charge of 1 coulomb
per second is a current of 1 ampere (amp).
repel

4. Michael Faraday (1791 –
1867)
Self-taught English chemist and physicist discovered electromagnetic induction in by which a changing magnetic field induces an electric field.
A capacitance of 1 coulomb per volt is called a farad (F)
Faraday’s electromagnetic induction ring

5. Joseph Henry (1797 – 1878)
American scientist, Princeton University professor, and first Secretary of the Smithsonian Institution.
Built the largest electromagnets of his day
Discovered self- induction
Unit of inductance, L, is the “Henry”

6. Magnetic Fields and Circuits
A current i through a coil produces a magnetic flux, , in webers, Wb.
   BgdA
  BA A
B = magnetic flux density in Wb/m2.
B  H
H = magnetic field intensity in A/m.
 = magnetic permeability
Hl  Ni
reluctance
F  R 
Ñ Hgdl  i
Ampere's Law:
Magnetomotive force F  Ni

7. Magnetic Flux Current entering "dots" produce fluxes that add.
Magnetic flux, , in webers, Wb.
11  flux in coil 1 produced by current in coil 1
12  flux in coil 1 produced by current in coil 2
21  flux in coil 2 produced by current in coil 1
22  flux in coil 2 produced by current in coil 2
1  total flux in coil 1  11  12
2  total flux in coil 2  21  22

8. Faraday's Law  N d1 1  N11 i Total flux linking coil 1:
Faraday's Law: induced voltage in coil 1 is
v (t)  d1 1
dt dt 1
Sign of induced voltage v1 is such that the current i through an external resistor would be opposite to the current i1 that produces the flux 1.
Example of Lenz's law
Symbol L of inductance from Lenz

9. Mutual Inductance  N1 11  N1 12 Faraday's Law
v1 (t)  N1 1
dt dt dt
In linear range, flux is proportional to current
di1 di2
v (t)  L L 1 11
dt dt 12
self-inductance
mutual inductance

10. Mutual Inductance M di2  L22 2 L di2 Linear media Let di1 di2
v (t)  L L 1 11 dt 12 dt
M di2 di di
v (t)  L di1
 L22 2
v2 (t)  L21 1
1 1 dt dt dt dt
L di2
Linear media
L12  L21  M
v (t)  M di1 2 dt 2 dt
Let
L2  L22
L1  L11

11. Core losses
Hysteresis losses

12. Hysteresis losses

13. Hysteresis losses

14. Eddy current losses

15. Eddy current losses How do we reduce Eddy current losses SOLID
LAMINATED

16. Eddy current losses

17. Eddy current losses in windings
Can be a problem with thick wires
Low voltage machines
High speed machines

18. Force, torque and power
Universal modeling of terminal characteristic of electro-magnetic devices based on energy balance

19. Induced EMF Induced emf could be classified into two types
Dynamically induced EMF.
Statically induced EMF.

20. Statically induced emf
In statically induced emf, conductor is stationary with respect to the magnetic field.
Transformer is an example of statically induced emf. Here the windings are stationary,magnetic field is moving around the conductor and produces the emf.

21. Statically induced emf
The emf produced in a conductor due to the change in magnetic field is called statically induce emf .It could be classified into two
1)self induced emf and 2)mutual induced emf

22. Dynamically induced emf
This is the EMF induced due to the motion of conductor in a magnetic field.
Mathematically
e = Blv volts
e-induced emf
B – flux density of magnetic field in Tesla
l = length of conductor in meters
v- velocity of conductor in m/s

23. Dynamically induced emf
If the conductor moves in an angle θ,the induced emf could be represented as
e= Blvsinθ
the direction of induced emf is given by flemmings right hand rule.
Generator is an example of dynamically induced emf.