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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.
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.
Effect of changing load on alternator?
by changing load its terminal voltage changes.
Why the rotor of an alternator at rated power dissipates more heat at a low power factor load?
In an alternator, the load current is supplied by the stator and the excitation is applied to the rotor. When the power factor is low (lagging), more excitation is required to maintain rated output voltage at rated current. More excitation is also required to maintain rated output voltage with increased output current. Increased excitation current means increased rotor losses that must be dissipated as heat. (akash)
What is the effect of change in load resistance on output voltage?
No.
Why does external voltage U decrease more with shunt than with separate excitation?
In shunt excitation, the field winding is connected in parallel with the armature, which means that the field current is influenced by the armature current. As load increases, the armature current rises, leading to a higher voltage drop across the armature resistance, which reduces the terminal voltage more significantly than in separate excitation. In separate excitation, the field winding has a constant supply independent of the armature current, maintaining a more stable voltage output under varying loads. Therefore, shunt excitation results in a greater decrease in external voltage due to the combined effects of increased armature current and associated voltage drop.
How do we usually think of voltage as the cause and currents the effect?
You apply a voltage across a load and the result is that a current flows through the load. So you must have the voltage present, the cause, before current flow, the effect. Think of voltage as pressure and current as flow.
What components comprise the excitation current of a transformer?
A transformer's excitation current can be resolved into two components. The first is in phase with the primary voltage, and is responsible for the losses. The second lags the supply voltage by 90 degrees, and is responsible for magnetising the core.
What does inductive load effect on High Voltage transmission line?
the inductive load which is generally use in high voltage transmission line known as transformer. the transformer transform the high voltage to low voltage.
How capacitor and resitor in a circuit effect the phase of input voltage?
A capacitor and a resistor has no effect on the supply voltage; however, this particular load combination will cause the load current to lead the supply voltage by some angle termed the 'phase angle'.
What is use of avr in excitation control system?
An Automatic Voltage Regulator (AVR) in an excitation control system is used to maintain a consistent output voltage level from a generator. It automatically adjusts the excitation current supplied to the generator's rotor, ensuring stable voltage under varying load conditions. This helps in enhancing the reliability and stability of electrical power systems by preventing voltage fluctuations and improving overall system performance. Additionally, AVRs can contribute to reactive power management and system efficiency.
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.
