10-04-2017, 09:20 PM
SEMINAR ON BRUSHLESS EXCITATION
[attachment=192]
INTRODUCTION
A new brushless excitation system is
described for a electrical motor having a
series resonant self commuted thyristor
inverter circuit.
Field excitation is provided by a
standard brushless excitationsystem
which consists of a rotating armature,
diode bridge and stationary field. The
brushless excitation system eliminates periodic brush and
collector ring maintenance and replacement.
NEEDS OF EXCITATION
According to FLEMING S RULE
When a field magnet is excited and its armature conductors are supplied with current from the supply mains , they experience a force tending to rotate the armature .
So for rotating the motor or
generating the power from the
generator we must require a
excited magnetic field.
The field excitation of motor
or generator is always by D.C
supply.
WHY EXCITATION IN D.C , WHY NOT IN A.C ???
According to Weber & Ewing s molecular Theory
The molecules of all substances are inherently
magnets in themselves, each having a N & S pole .
In the unmagnetised material electronic spin alignment is haphazard manner.
If we placed the unmagnetised material in a magnetic field or we give the D.C supply then the
Electronic spin start turn round their axis & arrange
Parallel to the magnetic field.
The arrangement of electronic spin results in N polarity at one end & the P polarity at the other.
TYPES OF EXCITATION
WITH BRUSH EXCITATION
The function of the brush is to collect current from Commutator.
It is usually made of carbon or graphite and are in
the shape of rectangular block.
It requires collector ring, brushes or commutator.
DISADVANTAGES
It require maintenance, adjustment & inspections.
It produces brush drop, spark, noise & friction loss.
It limits maximum speed of the machine.
The brushes assembly on a large machine is a costly
element.
CONCLUSION
Though I discussed about the brushless excitation. It is widely used in the present
scenario. Such as alternator and large motor. So excitation is the backbone of
Electrical Machine .