ELECTRICAL MACHINES – I

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.

1. ELECTRICAL MACHINES – I

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

3. André-Marie Ampère (1775 –
1836)
French mathematics professor who only
a week after learning of Oersted’s
discoveries in Sept. 1820 demonstrated
that parallel wires carrying currents
attract and repel each other.
attract
repel
A moving charge of 1 coulomb
per second is a current of
1 ampere (amp).

4. Michael Faraday (1791 –
1867)
Self-taught English chemist and physicist
discovered electromagnetic induction in
1831 by which a changing magnetic field
induces an electric field.
Faraday’s electromagnetic
induction ring
A capacitance of 1 coulomb per volt
is called a farad (F)

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

6. Magnetic Fields and Circuits
A current i through a coil produces a
magnetic flux, f, in webers, Wb.
BAf=
A
df=ò
B Ag
H = magnetic field intensity in A/m.
B = magnetic flux density in Wb/m
2
.
m=B H
m = magnetic permeability
Ampere's Law: d i=åò
H lgÑ
Hl Ni=
Ni=FMagnetomotive force f=F R
reluctance

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

8. Faraday's Law
1 1 1
Nl f=
Faraday's Law: induced voltage in coil 1 is
Sign of induced voltage v
1
is such that the current i through
an external resistor would be opposite to the current i
1
that
produces the flux f
1
.
Total flux linking coil 1:
1 1
1 1
( )
d d
v t N
dt dt
l f
= =
i
Example of Lenz's lawSymbol L of inductance from Lenz

9. Mutual Inductance
1 11 12
1 1 1 1
( )
d d d
v t N N N
dt dt dt
f f f
= = +
Faraday's Law
1 2
1 11 12
( )
di di
v t L L
dt dt
= +
In linear range, flux is proportional to current
self-inductance mutual inductance

10. Mutual Inductance
1 2
1 11 12
( )
di di
v t L L
dt dt
= +
1 2
2 21 22
( )
di di
v t L L
dt dt
= +
12 21
L L M= =
Linear media
1 2
1 1
( )
di di
v t L M
dt dt
= +
1 2
2 2
( )
di di
v t M L
dt dt
= +
2 22
L L=
1 11
L L=Let

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.