Magnetic Field Basic Concepts: A current carrying wire produces a magnetic field in the area around...
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Transcript of Magnetic Field Basic Concepts: A current carrying wire produces a magnetic field in the area around...
Magnetic Field
Basic Concepts:
A current carrying wire produces a magnetic field in the area around it.
A time changing magnetic field induces a voltage in a coil (wire) if is passes through the coil (transformer)
A moving wire in the presence of a magnetic field has a voltage induced in it (generator)
A current-carrying wire in the presence of a magnetic field has a force induced on it (motor).
Faraday’s Law- Induced voltage from a time-varying magnetic field
dt
deind
dt
dNeind
Faraday’s Law for a single wire
Faraday’s Law for a coil
If we define, :Then we have:
Flux linkage
N
dt
deind
Self and Mutual Inductance
2
2
.
NL
dt
diL
dt
diN
iNN
dt
dFN
dt
d
Ndt
d
dt
de
ps
ss
pp
NNM
NL
NL
2
2
In a coil In a transformer
Induced voltage on a conductor moving in a magnetic field
VBle
andif
VBle
e
ind
ind
ind
0 90
cossin
21
21
B).l(V
Direction of l is such that it would make the smallest angle with B)(V
The positive side of the resulted voltage in where B)(V points
AC excitation of magnetic circuits
What do we mean by AC excitation?1- Inserting sinusoid current (what we have considered so far)2- Applying sinusoid voltage Q: What happens if we somehow insert sinusoid current to a coil? Will the flux and induced voltage be sinusoid as well? A: No, because of saturation and hysteresis Q: What happens if we apply sinusoid voltage to a coil? Will the flux and current (magnetizing current) be sinusoid as well? A: No, because of saturation and hysteresis Conclusion: In a coil current and voltage cannot be sinusoid simultaneously. If one is sinusoid, the other is not.
tN
V
tdtVN
tVedt
dNe
m
m
m
sin..
cos.1
cos.
Let’s see what would happen if we apply sinusoid voltage to a coil?