on the basis of field excitation, dc generators are classified into the following types:-1- separetly excited dc generators
2-self excited dc generators
the behaviour of a dc generator on load depends upon the method of field excitation adopted
The excitation current is provided by a small self-excited pilot generator, attached to the same shaft as the alternator's rotor.
An alternator is just another name for a synchronous generator. Excitation is needed to create a magnetic field in the rotor. When to rotor is spun with excitation the magnetic field will cut through the stator field and produce an AC voltage in the stator field. In terms of an alternator with built in rectifier the stators AC voltage in the rectified to DC. The strength of excitation will determine the alternators output voltage. The AVR Automatic Voltage Regulator built into almost every alternator controls field current to maintain a constant output voltage.
A pole slip occurs when a motor or generator cannot maintain synchronicity. This occurs because the field excitation is too low.
In general terms, 'excitation' simply describes the process by which an electric current produces a magnetic field. But, more specifically, it refers to the creation of the magnetic field by the field windings of a motor or generator. In the case of an alternator, for example, the armature windings (the windings into which voltages are induced) are stationary, and inserted into slots cut into the inner face of the stator. The field is then provided by the rotor which is supplied (via slip rings) with a 'excitation' current provided by an external d.c. voltage.
The speed of a generator only effects the frequency. Most generators operate at 1800 RPM. The output voltage is controlled by varying the field excitation voltage.
the voltage which is given for creating magnetic field in a generator is known as excitation voltage.
A loss of field relay.
Over Excitation is a condition when the Excitation System is providing too much field current and as a result, the rotor of the generator will over heat. The Excitation System is equipped with an Over Excitation Limiter. This limiter acts to reduce the Excitation Current if this condition exists Underexcitation is a condition when the generator is not getting enough Excitation Current. If the generator does not get enough Excitation Current, it can be un-synchronized with the grid. We call this slipping a pole. If this occurs, the generator can be severely damaged. Kelly Thompson Engineering Lead Siemens Energy Alpharetta GA
Excitation is the phenomenon by which you control the excitation of field winding of a generator. In DC generator field winding is placed on stator and this field winding can be self excited or seperately excited depending upon the type on generator used. AC generators can also be self excited or seperately excited type but field winding is placed on rotor nad armature winding on stator.
For a small generator like the 125 Watt Alternator/Generator in your car, 12 Volts at a couple Amps. For a large 1,200,000,000 Power Plant Generator typical excitation is 600V at 8000A.
The difference between a separately excited DC generator and a Shunt DC generator is that for a separately excited Dc generator , the excitation field winding is supplied by an external source different from that supplying the armature while for shunt generator, the excitation field windind is connected in series with the armature and supplied by a single source.
The excitation current is provided by a small self-excited pilot generator, attached to the same shaft as the alternator's rotor.
The rotor must have a magnetic field in order to generator voltage in stator winding. The exciter circuit generates this DC filed in the rotor.
The excitation system is used to control the excitation of the rotating field in the armature. By increasing the armature current, it in turn increases the magnetic flux in the armature coil. This has the effect of increasing the voltage output of the generator. By lowering the armature current this in turn lowers the generator output voltage. The generator's voltage regulator automatically adjusts the output voltage continuously as the applied load on the generator changes.
loss of field protection is important because when a synchronous generator looses field excitation its acts as an induction generator and draws reactive power from the system which heats and damages rotor so as soon as the loss of field excitation is sensed the generator breaker should be opened as the rotor and the stator would both heat up and could damage. Best Regards, Ayaz Ahmed
An alternator is just another name for a synchronous generator. Excitation is needed to create a magnetic field in the rotor. When to rotor is spun with excitation the magnetic field will cut through the stator field and produce an AC voltage in the stator field. In terms of an alternator with built in rectifier the stators AC voltage in the rectified to DC. The strength of excitation will determine the alternators output voltage. The AVR Automatic Voltage Regulator built into almost every alternator controls field current to maintain a constant output voltage.
It is a DC voltage that is applied to the generator's revolving field windings. This produces a magnet field that cuts the generators main coil windings, inducing an electrical current within the main generator windings.