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Why field windings of synchronous alternator are excited by dc?
Wiki User
∙ 8y ago
The 'field'winding is in the rotor which rotates at the synchronous speed generating AC powerat the right frequency in the stator. That requires DC in the rotor. It is convenient because the DC is supplied to the rotor through slip rings, smooth polished rings which allow the carbon brushes to last a long time.
Wiki User
∙ 8y ago
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Does a induction motor need excitation?
The induction motor is the special kind of motor which runs below and above the synchronous speed. which the synchronous motor runs nearly equal the synchronous speed. The operation of synchronous motor runs with dc field excited hence separate dc field current is given to the field circuit. where as the induction motor the field and main field is drawn from the same supply hence no excitation is required. But due to this separate starting mechanism has to be required in case of the single phase induction motor.
Can you use the separately excited shunt generator machine as self excited generator?
You have a seperately excited generator and then you have a shunt generator which has the field winding in parallel with the armature terminals. In DC machines a separately excited generator could be run as a shunt generator provided the field winding is designed to work on the generated voltage. A separately excited alternator needs a DC supply for the field winding. In car alternators that is taken from the main winding via a rectifier and a voltage regulator.
What is a exciter generator?
its creates the magnetic field trough the electricity,which we called exciter for it.we send some electric shocks to the field coils,then it will magnetized the stater of the generator. When Diesel or petrol engine rotates the rotter of the generator, EXCITED stater act as a magnet. Depend on alternator`s design,rotter or stater one always EXITED to be a magnet. When engine turns the Alternator against the magnetic field,electricity is produced.
Where does the voltage that is necessary for field excitation on the rotor originates from?
The excitation current is provided by a small self-excited pilot generator, attached to the same shaft as the alternator's rotor.
What is excitation and why is it needed for start up in an AC generator?
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.
How Synchronous motor work with principal?
A synchronous motor comprises of a stator windings and a rotor with a squirrel cage and inside that is windings(coils). At starting, this motor is an induction motor running with slip. After the rotor has reached a certain speed, a DC current is applied to the windings inside the squirrel cage. A fixed field is induced in these windings. This field locks in with the synchronous rotating magnetic flux of the stator windings. The rotating stator windings then pull the rotor along. The amount of excitation current can be used to control the power factor of the motor, making this a popular type of motor for high power use with a constant mechanical load.
Why the synchronous machine rotate at synchronous speed?
The spatial distribution of the windings in the armature is designed in a way such that it produce a rotating field when a three phase source is applied to its terminals. The field windings have a DC field applied to it and it is rotated mechanically by a prime mover. If the prime mover tried to rotate the synchronous machine at speed higher than its synchronous value then the power output of the generator will increase and this causes the speed to "lock" again to the synchronous one. If the prime mover applied less torque then the machine will slow down but the power output will decrease DUE TO DECEASE in the applied torque and this cause the machine to "lock" again to synchronous speed of the grid. The same principle can be applied to synchronous motors except that torque is negative (i.e. the prime mover is applying negative torque)
Working principle of synchronus motor?
A synchronous motor is a three phase motor, which uses a magnetic field created by permanent magnets or a DC electromagnet on the rotor (usually). The stator windings have 3 phase voltages applied, and coupled with the DC field, create a rotating magnetic field that drives the motor at synchronous speed.
Working principle of 3 phase alternator?
A three-phase alternator has three sets of windings that produce three currents. The three currents make up the three phases. Together these produce the total AC output of the stator. An alternator is made up of a stator and a magnet rotor which is also known as the flywheel.
Does a induction motor need excitation?
The induction motor is the special kind of motor which runs below and above the synchronous speed. which the synchronous motor runs nearly equal the synchronous speed. The operation of synchronous motor runs with dc field excited hence separate dc field current is given to the field circuit. where as the induction motor the field and main field is drawn from the same supply hence no excitation is required. But due to this separate starting mechanism has to be required in case of the single phase induction motor.
What is the working principal of 3 phase alternator?
A 3 phase alternator is an AC electrical generator with 3 sets of windings in the stator. These windings overlap each other in phase angle, or timing relationship, by 120 degrees with respect to each other. The rotor (field or excitation) current is DC, and is adjusted to regulate the output power.
How a brush type 3 phase alternator works?
A pair of slip rings on the rotor carries current from the stationary brushes to the rotor windings in order to establish a magnetic field. As the alternator rotates, the magnetic field sweeps across the stator windings inducing an electric current in these windings. This current is an alternating current which is rectified via diodes and passed out of the alternator by means of the battery lead and (usually) the grounded alternator case. The battery voltage is sensed and used to vary the amount of current fed to the rotor in order to adjust the amount of current generated.
What keeps an alternator from overcharging?
An alternator is controlled by a voltage regulator. The regulator can be part of the alt., the computer, or a stand alone unit. The regulator controls the amount of current in the field windings which then controls the voltage output.
What is inductor alternator?
The armature and the field windings of an inductor alternator are both accommodated in the stator. The three phase ac armature windings are distributed in small slots and the dc field windings are concentrated in two slots in the stator. Each field coil spans half the total number of stator slots. Armature coils are connected in star and field coils are connected in series. The rotor resembles a cogged wheel, with no winding. The core of the stator, which is completely embraced by the field coils, will retain a residual magnetism if excited once. When the rotor is rotated, the passage of the rotor teeth alternatively under the field offers a varying reluctance path for the flux produced by the field coils. This flux, which varies periodically, links with the armature coils and induces an emf in them. The frequency of the induced emf depends on the speed of the rotor. The magnitude depends on the speed of the rotor as well as on the level of excitation. The armature and the field windings of an inductor alternator are both accommodated in the stator. The three phase ac armature windings are distributed in small slots and the dc field windings are concentrated in two slots in the stator. Each field coil spans half the total number of stator slots. Armature coils are connected in star and field coils are connected in series. The rotor resembles a cogged wheel, with no winding. The core of the stator, which is completely embraced by the field coils, will retain a residual magnetism if excited once. When the rotor is rotated, the passage of the rotor teeth alternatively under the field offers a varying reluctance path for the flux produced by the field coils. This flux, which varies periodically, links with the armature coils and induces an emf in them. The frequency of the induced emf depends on the speed of the rotor. The magnitude depends on the speed of the rotor as well as on the level of excitation.
Why sleep is occurs in three phase induction motor?
Slip is the relative difference between the speed of the rotating magnetic field of the stator windings and the speed of the rotor. The rotor must always run at a speed lower than the synchronous speed otherwise the rotor windings will not be cut by the magnetic field and hence no induced emf,no torque and the rotor will stand idle.
Why is speed not normally used to control the armature voltage of a synchronous alternator?
Because if speed was used, the power system frequency would be changed. A synchronous generator spins at synchronous speeds. Synchronous generators 101: A typical synchronous generator will have a field winding (typically on the rotor, or rotating part) and a stator winding (the stationary part where power is supplied to the power grid). Current is injected into the field winding, turning it into an electromagnet. This field current is controlled by the Automatic Voltage Regulator (AVR). The more current supplied to the field winding, the stronger the electromagnet becomes, and the more power is required from the prime mover (whatever is supplying the power - steam turbine, for example) to keep the generator spinning at synchronous speeds.
High voltage field windings are connected series or parallel?
high voltage field windings are connected in parallel
