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How does speed affects the generated emf in a self-excited generator?
to start a self excited generator you must remove the load the residual magnetism is the excitation starting with a load demagnetizes the all the iron dc generators are designed to have full field at operating voltage so voltage is constant over a pretty wide range of speeds ac can have permanent magnet embedded the shunt feild in the rotor keeps the voltage constant of course the frequency varies with rpm
Why terminal voltage of the self-excited shunt generator lower than that of the separately excited shunt generato?
Some generators are self excited; this means their terminal voltage is fed back to the excitation system to supply power to the rotor of the generator (which makes it into an electromagnet); the more power that is fed back, the stronger the electromagnet becomes, which makes it harder to turn the generator, which causes the generator to push out more power (simplified, really quick version). If there is a fault electrically near the terminal of a self excited generator, the terminal voltage will sage to near zero; this means the voltage supplied to the excitation system will drop by the same percentage (say the terminal voltage is 30% of what it should be, then the maximum supplied voltage to the excitation system drops to 30% of what it normally is, since P = V*I). Since the input power is less, the output of the generator will decrease (current will decrease). The terminal voltage is determined by the impedance between the generator and the fault such that V = I*Z; As I decreases, V will also continue to fall, causing the terminal voltage to sag even more. A non-self excited generator gets its' excitation power from the grid, specifically from a location that is electrically separated from its' terminal voltage. If the terminal voltage sagged to 30% (same fault location as above example), the excitation system voltage may be impacted slightly (say 2%) so the excitation system power is near maximum (98% for this example). Since the excitation system is much farther removed from the terminal voltage, it is not dependent upon it, thus the terminal voltage will not continue to sag as with a self excited system.
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.
For a 3 phase alternator why there is an AC voltage generated in the absence DC excitation?
due to residual magnetism
What are the reasons for for the decrease in terminal voltage of a seperately excited generator?
The decrease in terminal voltage of a separately excited generator can be attributed to several factors, including increased load demand, which causes a drop in output voltage due to the internal resistance of the generator. Additionally, losses such as copper losses (I²R losses) in the armature and excitation system, as well as core losses, can contribute to a reduction in voltage. Another factor could be a decrease in the excitation current, which reduces the magnetic field strength and subsequently lowers the generated voltage. Lastly, any faults or issues in the electrical connections or components can also lead to decreased terminal voltage.
How does speed affects the generated emf in a self-excited generator?
to start a self excited generator you must remove the load the residual magnetism is the excitation starting with a load demagnetizes the all the iron dc generators are designed to have full field at operating voltage so voltage is constant over a pretty wide range of speeds ac can have permanent magnet embedded the shunt feild in the rotor keeps the voltage constant of course the frequency varies with rpm
Difference between static excitation system?
It is called static excitation when you make use of solid state components like diode and thyristors to convert to pure dc and to use this dc for field excitation of synchronous generators. The field winding of synchronous generators can be excited by dc source only. It is called brushless excitation because use of carbon brushes are not made here.It is called dynamic excitation is when you make use of rotating brushes. Excitation is necessary to produce reactive power and also to regulate the voltage of synchronous generators.
Why terminal voltage of the self-excited shunt generator lower than that of the separately excited shunt generato?
Some generators are self excited; this means their terminal voltage is fed back to the excitation system to supply power to the rotor of the generator (which makes it into an electromagnet); the more power that is fed back, the stronger the electromagnet becomes, which makes it harder to turn the generator, which causes the generator to push out more power (simplified, really quick version). If there is a fault electrically near the terminal of a self excited generator, the terminal voltage will sage to near zero; this means the voltage supplied to the excitation system will drop by the same percentage (say the terminal voltage is 30% of what it should be, then the maximum supplied voltage to the excitation system drops to 30% of what it normally is, since P = V*I). Since the input power is less, the output of the generator will decrease (current will decrease). The terminal voltage is determined by the impedance between the generator and the fault such that V = I*Z; As I decreases, V will also continue to fall, causing the terminal voltage to sag even more. A non-self excited generator gets its' excitation power from the grid, specifically from a location that is electrically separated from its' terminal voltage. If the terminal voltage sagged to 30% (same fault location as above example), the excitation system voltage may be impacted slightly (say 2%) so the excitation system power is near maximum (98% for this example). Since the excitation system is much farther removed from the terminal voltage, it is not dependent upon it, thus the terminal voltage will not continue to sag as with a self excited system.
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.
Why 3 phase diesel generators run undervoltage?
The excitation voltage is too low. Turn the field voltage "pot" to raise the field voltage while watching the output generator voltage.
For a 3 phase alternator why there is an AC voltage generated in the absence DC excitation?
due to residual magnetism
What are the reasons for for the decrease in terminal voltage of a seperately excited generator?
The decrease in terminal voltage of a separately excited generator can be attributed to several factors, including increased load demand, which causes a drop in output voltage due to the internal resistance of the generator. Additionally, losses such as copper losses (I²R losses) in the armature and excitation system, as well as core losses, can contribute to a reduction in voltage. Another factor could be a decrease in the excitation current, which reduces the magnetic field strength and subsequently lowers the generated voltage. Lastly, any faults or issues in the electrical connections or components can also lead to decreased terminal voltage.
Why would a small amount of electricity be generated with no dc excitation?
A small amount of electricity can be generated without DC excitation due to the phenomenon of electromagnetic induction. When a conductor moves through a magnetic field, or when the magnetic field around a stationary conductor changes, an electromotive force (EMF) is induced. This can happen in various systems, such as in generators or even through residual magnetism in the system, allowing for the generation of small amounts of voltage without the need for external DC excitation.
If the excitation of generator changes what happens to the terminal voltage?
By Decreasing the excitation voltage the terminal voltage will decrease and similarly by increasing the excitation voltages the terminal voltage will also increases.
Generator excitation voltage?
the voltage which is given for creating magnetic field in a generator is known as excitation voltage.
How the KVAR supplied by synchronous generator?
Synchronous generators supply reactive power (measured in kilovolt-amperes reactive or KVAR) by adjusting their excitation level. When the excitation is increased, the generator can produce more reactive power, which is essential for voltage regulation in the power system. Conversely, if the excitation is decreased, the generator can absorb reactive power. This ability to control reactive power makes synchronous generators crucial for maintaining system stability and voltage levels in electrical grids.
What is dc separately excited shunt generator?
Either or both can be separately excited. To generate voltage you need a big magnet( the field). Most generators use an electro-magnet. Now the electro-magnet needs a source of power (electricity). We could use the generators own output to excite the field (magnet), this is called self excitation. The problem with self excitation is that we have to wait for the generator to turn and start generating, also to start generating (Building up) there must be some left over magnetism from the last time it was run (called residual magnetism) or not even a little voltage will be generated to start the field current flowing. To solve these problems we could use separately excited. This means we must have a separate source of power to excite the field to produce the magnetism. Sometimes a battery or gasoline driven generator is used to excite the field of a very large generator to get it generating and then we can use some of the generated output to either recharge the battery or switch over to from the battery. In any case we have adjustable control of the generator all the time. This is why most generators are designed to be separately excited. And that is why you car has a voltage regulator. It wakes up the alternator when the engine is started by separately exciting it (the field) with the battery and then regulates the output voltage of the alternator as the engine changes speed with the driver's commands from the gas pedal.
