The DC generator converts mechanical power into electrical power. The magnetic flux in a DC machine is produced by the field coils carry current. The circulating current in the field windings produces a magnetic flux, and the phenomenon is known as Excitation.
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.
What is an excitation system?
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.
What is excitation voltage?
An excitation voltage or current is the amount of electric energy ( D.C ) feed into the field winding of an alternator rotor to produce magnetic flux / field. … This lead to generate even more field strength and so more output voltage and so on and so on.
What is under excitation in generator?
Under-excitation limiter prevents the decrease of generator field current to the values lower than the stability margin or the thermal limit of end side of the stator core. … Tuning these limiters can be performed in different ways by considering the generator’s capability curves.
What are the 3 types of DC motors?
Main Types of DC Motors
- Permanent Magnet DC Motors. The permanent magnet motor uses a permanent magnet to create field flux. …
- Series DC Motors. In a series DC motor, the field is wound with a few turns of a large wire carrying the full armature current. …
- Shunt DC Motors. …
- Compound DC Motors.
What is back emf in dc motor?
When the armature of the DC motor rotates under the influence of driving torque, the armature of the conductors moves through a magnetic field inducing an emf in them. The induced emf is in the opposite direction to the applied voltage and is known as the back emf.
Why is excitation needed?
This varying magnetic flux induces AC currents in the stator windings of the synchronous machine. An excitation system is necessary since, without excitation current, the machine operates without field current and consequently, no voltage is generated (induced) in the stator windings of the machine.
What are the types of excitation system?
Three main types can be distinguished:
- DC excitation system,
- AC excitation system,
- Static excitation system.
- Block Schematic of Excitation Control:
- STATIC EXCITATION SYSTEM.
- BRUSHLESS EXCITATION SCHEME.
- AC EXCITATION SYSTEM.
- DC EXCITATION SYSTEM.
How does excitation system work?
The excitation system creates the electromagnetic field in the rotor. The stator has the armature winding that has the electrical energy induced. The stronger the magnetic field created, the stronger the electrical power produced. The strength of the magnetic field is adjusted by controlling the current to the rotor.
Why is excitation DC?
Excitation means producing a electrical magnetic field. If we rotate a wire in a constant magnetic field only then a electric current is produced. To get a constant magnetic field we have to apply a DC voltage to a coil. … The rotor needs to have a constant flux and that’s why the dc excitation is provided.
What is AVR?
An automatic voltage regulator (AVR) is an electronic device that maintains a constant voltage level to electrical equipment on the same load. The AVR regulates voltage variations to deliver constant, reliable power supply.
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 preset nominal level while running at its rated speed. So, without an excitation system, an AC alternator would be useless for its purpose.
What happen when generator loss excitation?
When a generator loses its excitation, the rotor current gradually decreases and the field voltage decays by the field time constant as well. In this case, the generator operates as an induction generator and draws reactive power from the power system instead of generating reactive power.
Which is the case of under excitation?
Hence in this case the motor is said to operate under lagging power factor and the is said to be under excited. CASE 3: If the field current is more than the normal field current, motor is said to be over excited.
Which is the case of under excitation EB V?
(i) Under excitation
be easily explained. Since Eb < V, the net voltage Er is decreased and turns clockwise. As angle ( δ δ = 90°) between Er and Ia is constant, therefore, phasor Ia also turns clockwise i.e., current Ia lags behind the supply voltage. Consequently, the motor has a lagging power factor.