It's applicable to any AC generator (more correctly called an
alternator, but commonly referred to as a "generator") driven by any
type of prime mover (torque-producing method). Generators convert torque
into electrical energy (power), which can easily be transmitted long
distance over wires, which can then be converted back into torque by
electric motors. (Come to think of it--that's why electrical energy is
produced: so torque can easily be transmitted over long distances from a
place where it is "abundant" to a place or places where it is not
available or can be used productively--notwithstanding for light and
heat, and for many: air conditioning (which requires torque!). Some of
the earliest large prime movers were hydro turbines, and the electrical
energy they produced was transmitted to factories and cities which were
loacted some distance away from the large rivers and falls.) Where the
torque that is input to the generator comes from is unimportant--turbine
(steam- or gas- or hydro- or wind turbine), reciprocating engine, steam
engine, they're all torque-producing methods.
Generators can be a watt (MW) load on the system--and they can also be a VAR load on the system. If the torque being applied to the generator rotor which is connected to an electrical grid is insufficient to maintain synchronous (rated) speed then the generator acutally becomes a motor. (Any torque produced by the prime mover over and above that necessary to maintain synchronous speed is converted by the generator, when connected to a grid, into watts (MW, depending on the size of the prime mover and generator.) This is sometimes called "motorizing" the generator--or "reverse power" because energy in the forom of watts is flowing INTO the generator and back into the prime mover instead of OUT of the generator. For some prime movers, this is VERY bad (like steam turbines, in particular) and there are reverse power detecting relays which will trip (open) the generator breaker when the reverse power exceeds a pre-set level to protect the prime mover.
In the same way, if the excitation being applied to the generator rotor is insufficient to keep the generator terminal voltage equal to the grid voltage, then VARs will begin to flow into the generator, and the generator will become a VAR load on the grid. (That's why this author doesn't understand why people want to operate their generators in a leading power factor configuration...unless they are trying to reduce the grid voltage by reducing excitation...it would sure be nice if someone would explain the reasoning behind the "necessity").
"Boost" and "buck" (terms certainly put into the lexicon by some Texan...) are sometimes used to describe under- and over-excitation, respectively. When the excitation being applied to the generator exceeds that required to maintain the generator terminal voltage equal to the grid voltage, the generator is said to be "boosting" the grid voltage, or, attempting to raise the grid voltage. The generator is then producing (supplying) VARs to the grid.
When the excitation being applied to the rotor (field) is insufficient to maintain the generator terminal voltage equal to the grid voltage, then the generator is said to be "bucking" the grid voltage, or, in effect, trying to reduce it. The net effect is to cause VARs to flow "into" the generator instead of out of the generator.
Any time current flows through a conductor, a magnetic field is generated. When the generator is connected to the grid and current is flowing through the stator (armature) conductors, magnetic fields associated with the armature windings are generated by virtue of the fact that AC current is flowing.
The VOLTAGE on the generator stator is a function of the excitation being applied, and voltage does NOT--by itself--produce flux. You can have 11,283 volts on a conductor, and if there is no current flowing there will be "no" flux field around the conductor. So, when the generator is NOT connected to the grid, the generator terminal voltage is a function of rotor field strength (and speed! but since alternators--in most parts of the world, anyway--operate at a fairly constant speed it's purely a function of rotor field strength, which is a function of excitation).
As a generator is "loaded", current flowing through the stator increases. As the current flow increases, so does the magnetic flux associated with the stator (armature) windings.
The stator (armature) flux "reacts" with the field flux--and generators are designed so that as long as it's applicable to any AC generator (more correctly called an alternator, but commonly referred to as a "generator") driven by any type of prime mover (torque-producing method). Generators convert torque into electrical energy (power), which can easily be transmitted long distance over wires, which can then be converted back into torque by electric motors. (Come to think of it--that's why electrical energy is produced: so torque can easily be transmitted over long distances from a place where it is "abundant" to a place or places where it is not available or can be used productively--notwithstanding for light and heat, and for many: air conditioning (which requires torque!). Some of the earliest large prime movers were hydro turbines, and the electrical energy they produced was transmitted to factories and cities which were loacted some distance away from the large rivers and falls.) Where the torque that is input to the generator comes from is unimportant--turbine (steam- or gas- or hydro- or wind turbine), reciprocating engine, steam engine, they're all torque-producing methods.
Generators can be a watt (MW) load on the system--and they can also be a VAR load on the system. If the torque being applied to the generator rotor which is connected to an electrical grid is insufficient to maintain synchronous (rated) speed then the generator acutally becomes a motor. (Any torque produced by the prime mover over and above that necessary to maintain synchronous speed is converted by the generator, when connected to a grid, into watts (MW, depending on the size of the prime mover and generator.) This is sometimes called "motorizing" the generator--or "reverse power" because energy in the forom of watts is flowing INTO the generator and back into the prime mover instead of OUT of the generator. For some prime movers, this is VERY bad (like steam turbines, in particular) and there are reverse power detecting relays which will trip (open) the generator breaker when the reverse power exceeds a pre-set level to protect the prime mover.
In the same way, if the excitation being applied to the generator rotor is insufficient to keep the generator terminal voltage equal to the grid voltage, then VARs will begin to flow into the generator, and the generator will become a VAR load on the grid. (That's why this author doesn't understand why people want to operate their generators in a leading power factor configuration...unless they are trying to reduce the grid voltage by reducing excitation...it would sure be nice if someone would explain the reasoning behind the "necessity").
"Boost" and "buck" (terms certainly put into the lexicon by some Texan...) are sometimes used to describe under- and over-excitation, respectively. When the excitation being applied to the generator exceeds that required to maintain the generator terminal voltage equal to the grid voltage, the generator is said to be "boosting" the grid voltage, or, attempting to raise the grid voltage. The generator is then producing (supplying) VARs to the grid.
When the excitation being applied to the rotor (field) is insufficient to maintain the generator terminal voltage equal to the grid voltage, then the generator is said to be "bucking" the grid voltage, or, in effect, trying to reduce it. The net effect is to cause VARs to flow "into" the generator instead of out of the generator.
Any time current flows through a conductor, a magnetic field is generated. When the generator is connected to the grid and current is flowing through the stator (armature) conductors, magnetic fields associated with the armature windings are generated by virtue of the fact that AC current is flowing.
The VOLTAGE on the generator stator is a function of the excitation being applied, and voltage does NOT--by itself--produce flux. You can have 11,283 volts on a conductor, and if there is no current flowing there will be "no" flux field around the conductor. So, when the generator is NOT connected to the grid, the generator terminal voltage is a function of rotor field strength (and speed! but since alternators--in most parts of the world, anyway--operate at a fairly constant speed it's purely a function of rotor field strength, which is a function of excitation).
As a generator is "loaded", current flowing through the stator increases. As the current flow increases, so does the magnetic flux associated with the stator (armature) windings.
The stator (armature) flux "reacts" with the field flux--and generators are designed so that as long as the flux reactions remain with a particular range, the generator will operate with minimal destructive heating issues.
However, when the rotor field flux is reduced "excessively" (i.e., the generator is running in an "excessive" underexcited condition), the flux field of the stator "expands" and "overpowers" the flux field of the rotor, and BAD heating happens.
That's what is meant by "armature reaction"--the interaction ("fighting" almost) of the stator flux and the field flux. A perfect example of armature reaction is what happens as a generator is "loaded." Usually, as a generator is loaded if the operator does NOT watch the VAR or power factor meter as the generator load is increased, VARs will be reduced and may even begin flowing into the generator, and the power factor will swing towards unity (1) and may even begin to decrease in the leading direction. This is because the strength of the magnetic field of the armature is increasing as current flow through the armature windings increases--and it tends to "overcome" or reduce the effective strength of the rotor field. Unless the Automatic (AC) voltage regulator is very well adjusted to the grid tendencies, the generator terminal voltage will decrease slightyly because of the reaction between the armature field and the rotor field as the armature field strength increases. So, that's why operators usually have to increase excitation as a generator is loaded--to increase rotor field strength which is being effectively reduced as the stator (armature) field strength increases as current flow through the stator (armature) increases. the flux reactions remain with a particular range, the generator will operate with minimal destructive heating issues.
However, when the rotor field flux is reduced "excessively" (i.e., the generator is running in an "excessive" underexcited condition), the flux field of the stator "expands" and "overpowers" the flux field of the rotor, and BAD heating happens.
That's what is meant by "armature reaction"--the interaction ("fighting" almost) of the stator flux and the field flux. A perfect example of armature reaction is what happens as a generator is "loaded." Usually, as a generator is loaded if the operator does NOT watch the VAR or power factor meter as the generator load is increased, VARs will be reduced and may even begin flowing into the generator, and the power factor will swing towards unity (1) and may even begin to decrease in the leading direction. This is because the strength of the magnetic field of the armature is increasing as current flow through the armature windings increases--and it tends to "overcome" or reduce the effective strength of the rotor field. Unless the Automatic (AC) voltage regulator is very well adjusted to the grid tendencies, the generator terminal voltage will decrease slightyly because of the reaction between the armature field and the rotor field as the armature field strength increases. So, that's why operators usually have to increase excitation as a generator is loaded--to increase rotor field strength which is being effectively reduced as the stator (armature) field strength increases as current flow through the stator (armature) increases.
Generators can be a watt (MW) load on the system--and they can also be a VAR load on the system. If the torque being applied to the generator rotor which is connected to an electrical grid is insufficient to maintain synchronous (rated) speed then the generator acutally becomes a motor. (Any torque produced by the prime mover over and above that necessary to maintain synchronous speed is converted by the generator, when connected to a grid, into watts (MW, depending on the size of the prime mover and generator.) This is sometimes called "motorizing" the generator--or "reverse power" because energy in the forom of watts is flowing INTO the generator and back into the prime mover instead of OUT of the generator. For some prime movers, this is VERY bad (like steam turbines, in particular) and there are reverse power detecting relays which will trip (open) the generator breaker when the reverse power exceeds a pre-set level to protect the prime mover.
In the same way, if the excitation being applied to the generator rotor is insufficient to keep the generator terminal voltage equal to the grid voltage, then VARs will begin to flow into the generator, and the generator will become a VAR load on the grid. (That's why this author doesn't understand why people want to operate their generators in a leading power factor configuration...unless they are trying to reduce the grid voltage by reducing excitation...it would sure be nice if someone would explain the reasoning behind the "necessity").
"Boost" and "buck" (terms certainly put into the lexicon by some Texan...) are sometimes used to describe under- and over-excitation, respectively. When the excitation being applied to the generator exceeds that required to maintain the generator terminal voltage equal to the grid voltage, the generator is said to be "boosting" the grid voltage, or, attempting to raise the grid voltage. The generator is then producing (supplying) VARs to the grid.
When the excitation being applied to the rotor (field) is insufficient to maintain the generator terminal voltage equal to the grid voltage, then the generator is said to be "bucking" the grid voltage, or, in effect, trying to reduce it. The net effect is to cause VARs to flow "into" the generator instead of out of the generator.
Any time current flows through a conductor, a magnetic field is generated. When the generator is connected to the grid and current is flowing through the stator (armature) conductors, magnetic fields associated with the armature windings are generated by virtue of the fact that AC current is flowing.
The VOLTAGE on the generator stator is a function of the excitation being applied, and voltage does NOT--by itself--produce flux. You can have 11,283 volts on a conductor, and if there is no current flowing there will be "no" flux field around the conductor. So, when the generator is NOT connected to the grid, the generator terminal voltage is a function of rotor field strength (and speed! but since alternators--in most parts of the world, anyway--operate at a fairly constant speed it's purely a function of rotor field strength, which is a function of excitation).
As a generator is "loaded", current flowing through the stator increases. As the current flow increases, so does the magnetic flux associated with the stator (armature) windings.
The stator (armature) flux "reacts" with the field flux--and generators are designed so that as long as it's applicable to any AC generator (more correctly called an alternator, but commonly referred to as a "generator") driven by any type of prime mover (torque-producing method). Generators convert torque into electrical energy (power), which can easily be transmitted long distance over wires, which can then be converted back into torque by electric motors. (Come to think of it--that's why electrical energy is produced: so torque can easily be transmitted over long distances from a place where it is "abundant" to a place or places where it is not available or can be used productively--notwithstanding for light and heat, and for many: air conditioning (which requires torque!). Some of the earliest large prime movers were hydro turbines, and the electrical energy they produced was transmitted to factories and cities which were loacted some distance away from the large rivers and falls.) Where the torque that is input to the generator comes from is unimportant--turbine (steam- or gas- or hydro- or wind turbine), reciprocating engine, steam engine, they're all torque-producing methods.
Generators can be a watt (MW) load on the system--and they can also be a VAR load on the system. If the torque being applied to the generator rotor which is connected to an electrical grid is insufficient to maintain synchronous (rated) speed then the generator acutally becomes a motor. (Any torque produced by the prime mover over and above that necessary to maintain synchronous speed is converted by the generator, when connected to a grid, into watts (MW, depending on the size of the prime mover and generator.) This is sometimes called "motorizing" the generator--or "reverse power" because energy in the forom of watts is flowing INTO the generator and back into the prime mover instead of OUT of the generator. For some prime movers, this is VERY bad (like steam turbines, in particular) and there are reverse power detecting relays which will trip (open) the generator breaker when the reverse power exceeds a pre-set level to protect the prime mover.
In the same way, if the excitation being applied to the generator rotor is insufficient to keep the generator terminal voltage equal to the grid voltage, then VARs will begin to flow into the generator, and the generator will become a VAR load on the grid. (That's why this author doesn't understand why people want to operate their generators in a leading power factor configuration...unless they are trying to reduce the grid voltage by reducing excitation...it would sure be nice if someone would explain the reasoning behind the "necessity").
"Boost" and "buck" (terms certainly put into the lexicon by some Texan...) are sometimes used to describe under- and over-excitation, respectively. When the excitation being applied to the generator exceeds that required to maintain the generator terminal voltage equal to the grid voltage, the generator is said to be "boosting" the grid voltage, or, attempting to raise the grid voltage. The generator is then producing (supplying) VARs to the grid.
When the excitation being applied to the rotor (field) is insufficient to maintain the generator terminal voltage equal to the grid voltage, then the generator is said to be "bucking" the grid voltage, or, in effect, trying to reduce it. The net effect is to cause VARs to flow "into" the generator instead of out of the generator.
Any time current flows through a conductor, a magnetic field is generated. When the generator is connected to the grid and current is flowing through the stator (armature) conductors, magnetic fields associated with the armature windings are generated by virtue of the fact that AC current is flowing.
The VOLTAGE on the generator stator is a function of the excitation being applied, and voltage does NOT--by itself--produce flux. You can have 11,283 volts on a conductor, and if there is no current flowing there will be "no" flux field around the conductor. So, when the generator is NOT connected to the grid, the generator terminal voltage is a function of rotor field strength (and speed! but since alternators--in most parts of the world, anyway--operate at a fairly constant speed it's purely a function of rotor field strength, which is a function of excitation).
As a generator is "loaded", current flowing through the stator increases. As the current flow increases, so does the magnetic flux associated with the stator (armature) windings.
The stator (armature) flux "reacts" with the field flux--and generators are designed so that as long as the flux reactions remain with a particular range, the generator will operate with minimal destructive heating issues.
However, when the rotor field flux is reduced "excessively" (i.e., the generator is running in an "excessive" underexcited condition), the flux field of the stator "expands" and "overpowers" the flux field of the rotor, and BAD heating happens.
That's what is meant by "armature reaction"--the interaction ("fighting" almost) of the stator flux and the field flux. A perfect example of armature reaction is what happens as a generator is "loaded." Usually, as a generator is loaded if the operator does NOT watch the VAR or power factor meter as the generator load is increased, VARs will be reduced and may even begin flowing into the generator, and the power factor will swing towards unity (1) and may even begin to decrease in the leading direction. This is because the strength of the magnetic field of the armature is increasing as current flow through the armature windings increases--and it tends to "overcome" or reduce the effective strength of the rotor field. Unless the Automatic (AC) voltage regulator is very well adjusted to the grid tendencies, the generator terminal voltage will decrease slightyly because of the reaction between the armature field and the rotor field as the armature field strength increases. So, that's why operators usually have to increase excitation as a generator is loaded--to increase rotor field strength which is being effectively reduced as the stator (armature) field strength increases as current flow through the stator (armature) increases. the flux reactions remain with a particular range, the generator will operate with minimal destructive heating issues.
However, when the rotor field flux is reduced "excessively" (i.e., the generator is running in an "excessive" underexcited condition), the flux field of the stator "expands" and "overpowers" the flux field of the rotor, and BAD heating happens.
That's what is meant by "armature reaction"--the interaction ("fighting" almost) of the stator flux and the field flux. A perfect example of armature reaction is what happens as a generator is "loaded." Usually, as a generator is loaded if the operator does NOT watch the VAR or power factor meter as the generator load is increased, VARs will be reduced and may even begin flowing into the generator, and the power factor will swing towards unity (1) and may even begin to decrease in the leading direction. This is because the strength of the magnetic field of the armature is increasing as current flow through the armature windings increases--and it tends to "overcome" or reduce the effective strength of the rotor field. Unless the Automatic (AC) voltage regulator is very well adjusted to the grid tendencies, the generator terminal voltage will decrease slightyly because of the reaction between the armature field and the rotor field as the armature field strength increases. So, that's why operators usually have to increase excitation as a generator is loaded--to increase rotor field strength which is being effectively reduced as the stator (armature) field strength increases as current flow through the stator (armature) increases.
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