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Why does the no-load characteristic differ for increasing and decreasing excitation current?
The no-load characteristic of a generator differs for increasing and decreasing excitation current due to magnetic hysteresis, residual magnetism, and core saturation effects.
When the excitation current increases, the magnetic domains in the iron core gradually align with the applied magnetic field, resulting in a higher generated electromotive force (EMF). However, as the excitation current decreases, these magnetic domains do not immediately return to their original unaligned state. This lag in realignment causes the generated voltage to remain higher during the decreasing phase of excitation than during the increasing phase at the same level of excitation current. This phenomenon is known as magnetic hysteresis.
Even when the excitation current is zero, the magnetic core retains some level of magnetisation, known as residual magnetism. This residual magnetic field means that when the excitation current starts increasing again, it takes additional current to overcome this residual alignment before the generated voltage rises significantly. As a result, the voltage is initially lower when increasing the excitation current from zero. Conversely, during the decreasing phase, the residual magnetism keeps the voltage higher than it would be if the core were fully demagnetised, further contributing to the difference between the increasing and decreasing curves.
As the excitation current increases, the magnetic core of the generator approaches saturation. Near saturation, any further increase in excitation current results in only a small increase in generated voltage because the core's magnetic domains are almost fully aligned. When the excitation current decreases from this saturated state, the magnetic domains gradually return to a less aligned state. This gradual realignment causes the generated voltage to decrease differently than it increased, contributing to the asymmetry between the increasing and decreasing excitation phases.
What else can I help you with?
What is the excitation system in a generator used for?
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.
What is transformer turns ratio excitation current?
This is the current level needed to energize a transformer to its rated voltageThe clue is in the name! 'Excitation' means to create a magnetic field. So the excitation current is the current drawn from the supply which sets up the magnetic field around the core.
If you increase or decrease the frequency what effect on electrical machin?
If you're talking about an electric motor, increasing the frequency will increase the speed of rotation of the motor, and decreasing the frequency will decrease the speed of rotation of the motor. The other way of controlling a motor is to control the current; increasing the current increases speed, decreasing current decreases speed.
Why do the readings differ for increasing and decreasing values of the incandescent lamp voltages?
...what readings? current? voltage? power? lux?
What is the difference between generator over excitation versus under excitation when attached to the grid?
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
Why does the no-load characteristic differ for increasing and decreasing excitation current in dc generator?
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What effects causes the difference in terminal voltage between the increasing and decreasing field excitation current?
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Why the armature current is increasing when the terminal voltage is decreasing?
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What is the excitation system in a generator used for?
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.
How can the current in a conductor be increased?
The current in a conductor can be increased by either increasing the voltage applied across the conductor or decreasing the resistance of the conductor.
How can you increase a current in a wire?
Ohm's law. Current is directly proportional to the applied emf and inversely proportional to the resistance in the circuit.
What are the factors that influence the speed of the direct-current shunt motor with increasing load?
.The magnitude of the voltage and current of both the armature and shunt field coil. To decrease the speed when the load is increasing then increase the shunt field current while decreasing the armature voltage or current. To increase the speed while the load is increasing then increase the armature current while decreasing the shunt field current. The decreasing and increasing of these currents and voltages can be done by connecting a variable resistor in series or parallel with each of the armature and/or shunt field coil.
How can you make an electric current stronger?
An electric current through a resistive circuit can be increased by decreasing the resistive load or increasing the voltage of the circuit.
What is transformer turns ratio excitation current?
This is the current level needed to energize a transformer to its rated voltageThe clue is in the name! 'Excitation' means to create a magnetic field. So the excitation current is the current drawn from the supply which sets up the magnetic field around the core.
What is meant by regulation or an alternator?
Regulation of an alternator is varying or adjusting the d.c. current flow (excitation current) in the revolving field coil to control the output voltage. When an alternator is subject to varying load conditions, and therefore changing load resistance at the output, the output voltage will vary in response. When output voltage is reduced in response to increased load (reduced output resistance), the "voltage regulator" will respond by increasing the excitation current to increase the voltage output. If load is reduced, the generator will momentarily become over-excited and the ouput voltage will increase. The voltage regulator responds by decreasing excitation current, returning the generator output voltage to its nominal level.
If you increase or decrease the frequency what effect on electrical machin?
If you're talking about an electric motor, increasing the frequency will increase the speed of rotation of the motor, and decreasing the frequency will decrease the speed of rotation of the motor. The other way of controlling a motor is to control the current; increasing the current increases speed, decreasing current decreases speed.
What would induce a greater electric current in a wire?
A greater electric current in a wire can be induced by increasing the voltage applied across the wire or decreasing the resistance of the wire. Both factors contribute to Ohm's Law (V=IR), where V is voltage, I is current, and R is resistance. Increasing the voltage or decreasing the resistance will lead to a higher current flowing through the wire.
