Every rotating electrical machine works based on Faraday's law. Every electrical machine requires a magnetic field and a coil (known as armature) with relative movement between them. In the case of an alternator, we supply electricity to the pole to produce a magnetic field and the output energy is removed from the armature. Due to the relative movement between the field and the armature, the armature conductor cuts off the flow of the magnetic field and, therefore, there would be changes in the flow connection with these armature conductors. According to Faraday's law of electromagnetic induction, there would be an induced emf in the armature. Thus, as soon as the load is connected to the armature terminals, there is a current flowing in the armature coil.
As soon as the current begins to flow through the armature conductor, there is a reverse effect of this current on the flow of the alternator's main field (or synchronous generator). This reverse effect is called an armature reaction in the alternator or synchronous generator. In other words, the effect of the armature flow (stator) on the flow produced by the poles in the rotor field is called the armature reaction.
We already know that a current conductor produces its own magnetic field, and that magnetic field affects the alternator's main magnetic field.
It has two undesirable effects: it distorts the main field or reduces the flow of the main field or both. They deteriorate the performance of the machine. When the field is distorted, it is known as a cross magnetization effect. And when the field flow is reduced, it is known as a demagnetizing effect.
The conversion of electromechanical energy takes place through the magnetic field as a medium. Due to the relative movement between the armature conductors and the main field, an emf is induced in the armature windings whose magnitude depends on the relative speed and magnetic flux. Due to the reaction of the armature, the flow is reduced or distorted, the induced net fraction is also affected and, therefore, the performance of the machine decreases.
Alternator armature reaction
In an alternator like all other synchronous machines, the effect of the armature reaction depends on the power factor, that is, the phase relationship between the terminal voltage and the armature current.
Reactive power (delay) is the energy of the magnetic field; therefore, if the generator supplies a delayed load, it implies that it is supplying the load with magnetic energy. As this energy comes from the excitation of the synchronous machine, the net reactive energy is reduced in the generator.
Therefore, the reaction of the armature is demagnetizing. Likewise, the armature reaction has a magnetizing effect when the generator supplies an initial charge (as the main charge carries the main VAR) and, in return, supplies delayed VAR (magnetic energy) to the generator. In the case of a purely resistive load, the armature reaction is only cross-magnetized.
The reaction of the alternator armature or synchronous generator depends on the phase angle between the stator armature current and the voltage induced in the alternator armature winding.
The phase difference between these two quantities, that is, current and voltage of the armature, can vary from - 90o to + 90o
If that angle is θ, then
To understand the real effect of this angle on the alternator armature reaction, we’ll consider three standard cases,
When θ = 0
When θ = 90o
When θ = - 90o
The reaction of alternator armature in unit power factor
In the power factor of the unit, the angle between the armature current I and the induced emf E is zero. This means that the armature current and the induced emf are in the same phase. But we know theoretically that the EMF induced in the armature is due to the change in the flow of the main field, connected to the armature conductor.
As the field is excited by DC, the main flow of the field is constant with the field magnets, but it would be alternated with the armature, as there is a relative movement between the field and the armature in the alternator. If the flow of the alternator's main field with the armature can be represented as
Then the induced emf through the armature is proportional to dɸf / dt.
Therefore, from these equations (1) and (2) above, it is clear that the angle between, φf and the induced emf will be 90o.
Now, the armature flow φa is proportional to the armature current I. Therefore, the armature flow is in phase with the armature current I.
Again, in the unit, the electric power factors I and E are in the same phase. Therefore, in the power factor of the unit, is in phase with E. Therefore, in this condition, the armature flow is in phase with the induced EMF and the field flow is in quadrature with E. Therefore, the armature flow φa is square to the main field flow φf.
As these two flows are perpendicular to each other, the reaction of the alternator armature in the power factor of the unit is of the type of distortion or cross magnetization.
As the armature flow pushes the main field flow perpendicularly, the main field flow distribution under one face of the pole does not remain uniformly distributed. The density of the flow under the tips of the poles on the right increases slightly, while under the tips of the poles in front it decreases.
Alternator armature reaction in delayed zero power factor
At the zero delay power factor, the armature current is 90o for the emulsion induced in the armature.
Like the emf induced in the armature coil due to the main field flow, the emf takes the main field flow by 90o. From equation (1) we obtain the field flow,
Therefore, at ωt = 0, E is maximum and φf is zero.
At ωt = 90o, E is zero and φf has the maximum value.
At ωt = 180o, E is maximum and φf zero.
At ωt = 270o, E is zero and φf has a maximum negative value.
Here, got the maximum value 90 ° before E. Therefore leads E by 90 °.
Now, the armature current I is proportional to the armature flow φa and I is E at 90o. Therefore, is E at 90o.
Thus, it can be concluded that the flux of field flow takes E at 90o.
Therefore, the armature flow and the field flow act directly opposite to each other. Thus, the alternator armature reaction in the zero delay power factor is a purely demagnetizing type. This means that the flow of the armature directly weakens the flow of the main field.
The reaction of alternator armature in the main power factor
In the condition of the main power factor, the armature current "I" induces the fem E by an angle of 90o. Again, we show only the derived leads field flow, induced by EME by 90o.
Again, the armature flow φa is proportional to the armature current I. Therefore, φa is in phase with I. Therefore, the armature flow φa also takes E, at 90o, as I conduct E, at 90o.
As in this case, both the flux of the armature and the lead of the flux of the field, induced by the fem E by 90o, it can be said that the flux of the field and the flux of the armature are in the same direction. Therefore, the resulting flow is simply the arithmetic sum of the field flow and the armature flow. Therefore, finally, it can be said that the alternator armature reaction due to a purely main electrical power factor is the type of magnetization.
As soon as the current begins to flow through the armature conductor, there is a reverse effect of this current on the flow of the alternator's main field (or synchronous generator). This reverse effect is called an armature reaction in the alternator or synchronous generator. In other words, the effect of the armature flow (stator) on the flow produced by the poles in the rotor field is called the armature reaction.
We already know that a current conductor produces its own magnetic field, and that magnetic field affects the alternator's main magnetic field.
It has two undesirable effects: it distorts the main field or reduces the flow of the main field or both. They deteriorate the performance of the machine. When the field is distorted, it is known as a cross magnetization effect. And when the field flow is reduced, it is known as a demagnetizing effect.
The conversion of electromechanical energy takes place through the magnetic field as a medium. Due to the relative movement between the armature conductors and the main field, an emf is induced in the armature windings whose magnitude depends on the relative speed and magnetic flux. Due to the reaction of the armature, the flow is reduced or distorted, the induced net fraction is also affected and, therefore, the performance of the machine decreases.
Alternator armature reaction
In an alternator like all other synchronous machines, the effect of the armature reaction depends on the power factor, that is, the phase relationship between the terminal voltage and the armature current.
Reactive power (delay) is the energy of the magnetic field; therefore, if the generator supplies a delayed load, it implies that it is supplying the load with magnetic energy. As this energy comes from the excitation of the synchronous machine, the net reactive energy is reduced in the generator.
Therefore, the reaction of the armature is demagnetizing. Likewise, the armature reaction has a magnetizing effect when the generator supplies an initial charge (as the main charge carries the main VAR) and, in return, supplies delayed VAR (magnetic energy) to the generator. In the case of a purely resistive load, the armature reaction is only cross-magnetized.
The reaction of the alternator armature or synchronous generator depends on the phase angle between the stator armature current and the voltage induced in the alternator armature winding.
The phase difference between these two quantities, that is, current and voltage of the armature, can vary from - 90o to + 90o
If that angle is θ, then
To understand the real effect of this angle on the alternator armature reaction, we’ll consider three standard cases,
When θ = 0
When θ = 90o
When θ = - 90o
The reaction of alternator armature in unit power factor
In the power factor of the unit, the angle between the armature current I and the induced emf E is zero. This means that the armature current and the induced emf are in the same phase. But we know theoretically that the EMF induced in the armature is due to the change in the flow of the main field, connected to the armature conductor.
As the field is excited by DC, the main flow of the field is constant with the field magnets, but it would be alternated with the armature, as there is a relative movement between the field and the armature in the alternator. If the flow of the alternator's main field with the armature can be represented as
Then the induced emf through the armature is proportional to dɸf / dt.
Therefore, from these equations (1) and (2) above, it is clear that the angle between, φf and the induced emf will be 90o.
Now, the armature flow φa is proportional to the armature current I. Therefore, the armature flow is in phase with the armature current I.
Again, in the unit, the electric power factors I and E are in the same phase. Therefore, in the power factor of the unit, is in phase with E. Therefore, in this condition, the armature flow is in phase with the induced EMF and the field flow is in quadrature with E. Therefore, the armature flow φa is square to the main field flow φf.
As these two flows are perpendicular to each other, the reaction of the alternator armature in the power factor of the unit is of the type of distortion or cross magnetization.
As the armature flow pushes the main field flow perpendicularly, the main field flow distribution under one face of the pole does not remain uniformly distributed. The density of the flow under the tips of the poles on the right increases slightly, while under the tips of the poles in front it decreases.
Alternator armature reaction in delayed zero power factor
At the zero delay power factor, the armature current is 90o for the emulsion induced in the armature.
Like the emf induced in the armature coil due to the main field flow, the emf takes the main field flow by 90o. From equation (1) we obtain the field flow,
Therefore, at ωt = 0, E is maximum and φf is zero.
At ωt = 90o, E is zero and φf has the maximum value.
At ωt = 180o, E is maximum and φf zero.
At ωt = 270o, E is zero and φf has a maximum negative value.
Here, got the maximum value 90 ° before E. Therefore leads E by 90 °.
Now, the armature current I is proportional to the armature flow φa and I is E at 90o. Therefore, is E at 90o.
Thus, it can be concluded that the flux of field flow takes E at 90o.
Therefore, the armature flow and the field flow act directly opposite to each other. Thus, the alternator armature reaction in the zero delay power factor is a purely demagnetizing type. This means that the flow of the armature directly weakens the flow of the main field.
The reaction of alternator armature in the main power factor
In the condition of the main power factor, the armature current "I" induces the fem E by an angle of 90o. Again, we show only the derived leads field flow, induced by EME by 90o.
Again, the armature flow φa is proportional to the armature current I. Therefore, φa is in phase with I. Therefore, the armature flow φa also takes E, at 90o, as I conduct E, at 90o.
As in this case, both the flux of the armature and the lead of the flux of the field, induced by the fem E by 90o, it can be said that the flux of the field and the flux of the armature are in the same direction. Therefore, the resulting flow is simply the arithmetic sum of the field flow and the armature flow. Therefore, finally, it can be said that the alternator armature reaction due to a purely main electrical power factor is the type of magnetization.
Nature of the armature reaction
- The reaction flow of the armature is constant in magnitude and rotates at synchronous speed.
- The armature reaction is cross-magnetized when the generator provides a load on the unit's power factor.
- When the generator provides a load on the main power factor, the armature reaction is partially demagnetized and partially crossed magnetized.
- When the generator provides a load on the main power factor, the armature reaction is partially magnetized and partially crossed magnetized.
- The armature flow acts independently of the main field flow.
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