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How can the field coils of a dc machine be connected with self excitation?
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∙ 9y ago
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∙ 9y ago
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What 3 factors that affect the output of a generator?
1:The strenght of the main magnetic Field. Determined by the strenght of the field magnets in a permanent magnet machine, or by the number of turns of wire on the field coils and the current through the coils in a wound field machine.2: The number of armature conductors connected in series, which cut the main magnetic field. Determined by the number of turns on armature coils and weather the armature is lap or wave wound, which determines the number of armature conductors connected in series.3: The speed at which the armature conductors cut the main magnetic field. The faster the armature cuts the magnetic Field, the higher will be the value of the voltage generated in the machine
What is excitation of DC machine?
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.
What is cross field principle?
A seperately excitd 2pole dc generator consitstng of many cnoductors rotating in magneti2 field producd by field coils with no load connected to it
What is meant by flashing a field in excitation?
A generator needs to have residual magnetism in its field coils to start the generation of electricity. A generator that has not been run in a long time will loose this magnetism. Because the field voltage is a DC supply, a battery across the field wiring will energize the coils instantaneously. Doing this several times will cause sparking when the contact to the battery is broken, hence the flash. This intermittent energizing and de-energizing will bring the residual magnetism back into the field coils. When the generator is started, the voltage output should rise to its normal level. If it does the magnetizing of the field coils to bring back the residual magnetism will have worked.
How the DC generator are classified according to field excitation?
on the basis of field excitation, dc generators are classified into the following types:-1- separetly excited dc generators2-self excited dc generatorsthe behaviour of a dc generator on load depends upon the method of field excitation adopted
How generator operates?
It works with two reactor coils for excitation of the field reactor coil , which in turn provides current to the field. The two reactor coils are connected in shunt and series with the output of the generator stator or armature ( from where load is connected).
How can the field coils of DC machines be connected with self excited machines?
No
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.
What 3 factors that affect the output of a generator?
1:The strenght of the main magnetic Field. Determined by the strenght of the field magnets in a permanent magnet machine, or by the number of turns of wire on the field coils and the current through the coils in a wound field machine.2: The number of armature conductors connected in series, which cut the main magnetic field. Determined by the number of turns on armature coils and weather the armature is lap or wave wound, which determines the number of armature conductors connected in series.3: The speed at which the armature conductors cut the main magnetic field. The faster the armature cuts the magnetic Field, the higher will be the value of the voltage generated in the machine
What is excitation of DC machine?
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.
If a magnet is put inside one coil of wire a voltage is produced. What will happen if the magnet is put inside two coils of wire?
I would expect a voltage in both coils of wire.Note that, if the two coils are connected, the voltages (and corresponding currents) in the coils can interact. Also, if the two coils are NOT connected, they can STILL interact, since a current will produce its own magnetic field.
What is cross field principle?
A seperately excitd 2pole dc generator consitstng of many cnoductors rotating in magneti2 field producd by field coils with no load connected to it
In synchronous motor theory is excitation current the same as field current?
yes. excitation current is same as field current to my knowledge
How do electric generators convert kinetic energy into electrical energy?
They revolve sets of coils of wire across a strong magnetic field, and this induces electrical currents in the coils. NB The current will only flow if thetwo ends of the coils are connected, and this is achieved by whatever circuit is connected to the generator's output.
What is meant by flashing a field in excitation?
A generator needs to have residual magnetism in its field coils to start the generation of electricity. A generator that has not been run in a long time will loose this magnetism. Because the field voltage is a DC supply, a battery across the field wiring will energize the coils instantaneously. Doing this several times will cause sparking when the contact to the battery is broken, hence the flash. This intermittent energizing and de-energizing will bring the residual magnetism back into the field coils. When the generator is started, the voltage output should rise to its normal level. If it does the magnetizing of the field coils to bring back the residual magnetism will have worked.
Explain the working principle of shunt generator?
A shunt generator is a machine with a rotating set of coils of wire embedded in the iron core in its armature (the spinning part), and a 'commutator' and brushes that carry the current from the (spinning) windings on the armature to the stationary external electrical load. It also has a 'field' winding that creates a stationary magnetic field inside the machine, that the armature coils are spun in. As the windings spin, they cut the stationary field and generate an alternating voltage. As well as providing a moving connection to the coils, the commutator and brushes act like a switch, reversing the connections from the coils to the external circuit each time the waveform changes polarity from positive to negative and vice versa. This creates direct current in the external circuit and load. In a shunt generator, the field windings are connected in parallel with the armature ('shunt' is a common term for 'in parallel') and the field gets its power ('excitation') from the armature - the machine is 'self-excited'. A self-excited generator needs a small 'residual field' in the field's iron core so it can generate a small output from the armature when starting, which is fed to the field, boosting the armature output, which is fed to the field.... and so on, until the field iron core saturates with flux, and the field stops strengthening. Shunt generators are the 'workhorse of the small generator market - they are cheap and simple, have an output voltage that 'droops' a little with increasing load, and most shunt generators can safely be short-circuited - this takes the electrical energy away from the field, and the armature can usually develop only a small output current - not enough to damage it.
Generator excitation voltage?
the voltage which is given for creating magnetic field in a generator is known as excitation voltage.
