This
Direct Current (DC)
is called excitation current. Which is required to generate magnetic flux in the rotor circuit. 2.
What is rotor excitation?
An electric generator or electric motor consists of a rotor
spinning in a magnetic field
. … The process of generating a magnetic field by means of an electric current is called excitation.
Is the excitation current of a synchronous motor AC or DC?
Hence, it comes under electromagnetic device. It receives 3 phase AC electrical supply to its armature winding and
DC
supply is provided to rotor winding. Synchronous motor excitation refers to the DC supply given to rotor which is used to produce the required magnetic flux.
Why DC is used for excitation?
Why only D.C is used for Excitation in Alternators?
Excitation voltage or current is supplied to the field windings of a rotor to produce a static magnetic field
. If we use alternating current instead of direct current; we will get a fluctuating magnetic field.
Is AC alternator rotor excitation current AC or DC?
The exciter has its field winding
(DC current)
in the stator and armature winding in the rotor. In the case of an AC exciter generator, the three-phase AC is induced in the rotor winding, which is rectified using diode, thyristor, or transistor bridge installed in the rotor.
Does alternator need excitation?
Without the excitation system the AC alternator would have no way of building its voltage as it starts to rotate, nor would not be able to regulate its voltage to the pre-set nominal level while running at its rated speed. So, without an excitation system, an AC
alternator would be useless for its purpose
.
How many types of excitation are there?
There are
nineteen different excitation
types in three major groups: Direct Current Commutator Exciters (type DC), Alternator Supplied Rectifier Excitation Systems (type AC) and Static Excitation Systems (type ST).
What are excitation methods?
Excitation systems can be defined as the system that provides field current to the rotor winding of a generator. Well-designed excitation systems provide reliability of operation, stability and fast transient response. The four common excitation methods include:
Shunt or Self Excited
.
Why does DC excitation is used rather than AC excitation?
In the alternator, as the rotor conductor changes its position as the rotor rotating so
constant flux is to
be produced in the rotor winding and it is possible only when the DC supply is given to the rotor winding. … As we need constant flux that is why DC is used instead of AC for excitation of Synchronous Alternator.
What is self excitation?
a
kind of excitation of generators where the magnetic field of the main poles is excited by a current
supplied to the windings of the main poles from the armature (rotor) winding. … Self-excitation is made use of most often in DC generators.
What happens if excitation is changed?
A change in the excitation, thus, affects only the power factor of its output. … This
reduces the terminal voltage slightly
, so let the excitation of the first alternator be increased so as to bring the terminal voltage back to its original value.
Why do we use synchronous motors?
The advantages of the synchronous motor are
the ease with which the power factor can be controlled and the constant rotational speed of the machine
, irrespective of the applied load. Synchronous motors, however, are generally more expensive and a d.c. supply is a necessary feature of the rotor excitation.
Why synchronous motors are not self starting?
Above a certain size, synchronous motors are not self-starting motors. This property is
due to the inertia of the rotor
; it cannot instantly follow the rotation of the magnetic field of the stator. … Once the rotor nears the synchronous speed, the field winding is excited, and the motor pulls into synchronization.
How does a DC exciter work?
DC Exciter
Control of the exciter output is done by
varying the field current of the exciter
. This output from the exiter then controls the magnetic field of the rotor to produce a constant voltage output by the generator. This DC current feeds to the rotor through slip rings.
What is excitation AC excitation and DC excitation?
The exciter stator has
residual magnetism
when the rotor starts rotating AC (Alternating Current) output is generated in the exciter rotor coils and this output is passed through a bridge rectifier. The output passed through a bridge rectifier is converted into DC (Direct Current) and given to the main rotor.
What is excitation in DC motor?
The
magnetic flux
in a d.c machine is produced by field coils carrying current. The production of magnetic flux in the device by circulating current in the field winding is called excitation.
