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How do I fix the speed of a generator?
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If I need to generate power at a specified frequency, then I need to make sure that the rotor of the generator rotates at a specified speed (rpm). But when I am rotating it with steam or water how do I control this speed? It seems to me that the mechanical forces that rotate the generator somehow has to balance to achieve this. How exactly is this done?
electric-machine
asked 47 mins ago
praveen kr
1133
add a comment |Â
up vote
1
down vote
favorite
If I need to generate power at a specified frequency, then I need to make sure that the rotor of the generator rotates at a specified speed (rpm). But when I am rotating it with steam or water how do I control this speed? It seems to me that the mechanical forces that rotate the generator somehow has to balance to achieve this. How exactly is this done?
electric-machine
asked 47 mins ago
praveen kr
1133
With some sort of throttle on the prime mover, adjusted so that power in equals power out (plus internal losses).
– Dave Tweed♦
42 mins ago
I'm pretty sure that large generators attached to mains are forced into synchronicity by the influence of all the other things attached to mains; if the generator slows down any, there would be a motor torque applied by the mains power pulling it back towards synchronous speed, and likewise if it speeds up. This is a problem in itself rather than a solution, though, because if your generator starts running as a motor it's likely to tear itself or things attached to its shaft apart; it's not made to operate like that.
– Felthry
35 mins ago
add a comment |Â
up vote
1
down vote
favorite
up vote
1
down vote
favorite
If I need to generate power at a specified frequency, then I need to make sure that the rotor of the generator rotates at a specified speed (rpm). But when I am rotating it with steam or water how do I control this speed? It seems to me that the mechanical forces that rotate the generator somehow has to balance to achieve this. How exactly is this done?
electric-machine
asked 47 mins ago
praveen kr
1133
If I need to generate power at a specified frequency, then I need to make sure that the rotor of the generator rotates at a specified speed (rpm). But when I am rotating it with steam or water how do I control this speed? It seems to me that the mechanical forces that rotate the generator somehow has to balance to achieve this. How exactly is this done?
electric-machine
electric-machine
asked 47 mins ago
praveen kr
1133
asked 47 mins ago
praveen kr
1133
asked 47 mins ago
praveen kr
1133
asked 47 mins ago
praveen kr
1133
asked 47 mins ago
praveen kr
1133
1133
With some sort of throttle on the prime mover, adjusted so that power in equals power out (plus internal losses).
– Dave Tweed♦
42 mins ago
I'm pretty sure that large generators attached to mains are forced into synchronicity by the influence of all the other things attached to mains; if the generator slows down any, there would be a motor torque applied by the mains power pulling it back towards synchronous speed, and likewise if it speeds up. This is a problem in itself rather than a solution, though, because if your generator starts running as a motor it's likely to tear itself or things attached to its shaft apart; it's not made to operate like that.
– Felthry
35 mins ago
add a comment |Â
With some sort of throttle on the prime mover, adjusted so that power in equals power out (plus internal losses).
– Dave Tweed♦
42 mins ago
I'm pretty sure that large generators attached to mains are forced into synchronicity by the influence of all the other things attached to mains; if the generator slows down any, there would be a motor torque applied by the mains power pulling it back towards synchronous speed, and likewise if it speeds up. This is a problem in itself rather than a solution, though, because if your generator starts running as a motor it's likely to tear itself or things attached to its shaft apart; it's not made to operate like that.
– Felthry
35 mins ago
With some sort of throttle on the prime mover, adjusted so that power in equals power out (plus internal losses).
– Dave Tweed♦
42 mins ago
With some sort of throttle on the prime mover, adjusted so that power in equals power out (plus internal losses).
– Dave Tweed♦
42 mins ago
I'm pretty sure that large generators attached to mains are forced into synchronicity by the influence of all the other things attached to mains; if the generator slows down any, there would be a motor torque applied by the mains power pulling it back towards synchronous speed, and likewise if it speeds up. This is a problem in itself rather than a solution, though, because if your generator starts running as a motor it's likely to tear itself or things attached to its shaft apart; it's not made to operate like that.
– Felthry
35 mins ago
I'm pretty sure that large generators attached to mains are forced into synchronicity by the influence of all the other things attached to mains; if the generator slows down any, there would be a motor torque applied by the mains power pulling it back towards synchronous speed, and likewise if it speeds up. This is a problem in itself rather than a solution, though, because if your generator starts running as a motor it's likely to tear itself or things attached to its shaft apart; it's not made to operate like that.
– Felthry
35 mins ago
add a comment |Â
4 Answers
4
active
oldest
votes
up vote
2
down vote
accepted
Electrically
Some systems do this electrically. The generator either generates DC, or the variable-frequency AC is rectified to make DC, and then an inverted makes the desired AC frequency. Common on more modern small wind turbines.
Mechanically
Other systems are mechanically controlled to get the desired frequency. The mechanism used would be called a governor. Most simple mechanical governors are not very accurate, so this would not be good enough for a grid connected device. It is also possible to make more accurate governors which work mechanically in a similar way to the paragraph below, these are commonly used on internal combustion engines.
With Feedback
Another approach, and probably the most common is to have some form of feedback. A microcontroller monitors the frequency being generated, and adjusts the mechanical system via some form of servo to get the right frequency. For example, it could open and close a sluice gate to adjust the water flow through a turbine. A more complicated system could adjust both a sluice gate and the turbine blades to keep the correct frequency while also varying the output power.
Grid Synchronous operation
In some cases, it might not be necessary at all. If you have a small wind turbine, connected to the mains grid near a coal power station, you could just hook it up and forget about it. The huge turbines in the power station will stabilise the grid frequency, and fix the rotation speed of the wind turbine. If the wind blows harder, you'll just get more current, and a slight power factor shift. Note that as more and more wind turbines get added, the folks who run the power station will get less and less happy about this, so the grid operator will eventually ban it.
answered 36 mins ago
Jack B
9,72612136
It's probably worth mentioning doubly-fed induction machines here. They use an induction machine simultaneously as both a generator and a rotary converter to keep the output frequency constant with varying input frequencies.
– Felthry
32 mins ago
@Felthry I didn't include them because I'm not sufficiently familiar with them. Feel free to propose an edit though.
– Jack B
29 mins ago
I would, but Andy's answer already takes care of that.
– Felthry
5 mins ago
add a comment |Â
up vote
2
down vote
A lot of wind generators use a doubly fed induction generator (DFIG): -
They can convert power at one frequency to another frequency i.e. they can produce 50/60 Hz even though the rotor may be running too slowly. This is done by injection of an AC current into the rotor coils. The control system that acheives this may also be able to alter pitch angle of the turbine as another means of increasing or decreasing mechanical rotation speed.
For more information please read this EE answer.
answered 28 mins ago
Andy aka
233k10172397
add a comment |Â
up vote
1
down vote
That is what a governor is for.
The mechanical version is a device that will use centrifugal force or a blower to actuate the throttle/intake to slow down the engine when the speed climbs too much.
You can make it electronic with an RPM sensor and a electronically controlled throttle/intake.
answered 43 mins ago
ratchet freak
2,4401011
add a comment |Â
up vote
1
down vote
In my (limited) experience of generator design, you have to look at multiple factors:
Speed of mechanical input (turbine, wheel etc)
Power of mechanical input
Output voltage
Output current
Output power (which depends on voltage and current, but you usually want to maximise this, at a peak power point)
In many cases what you want to maintain is a constant voltage output, which will vary with the electrical load; higher current would make the output drop.
In your set up, you only care about the speed of the shaft (for whatever reason that is). There are two ways to do this: control input power or control output power.
If you know that your mechanical power will always be more than the output power, you could use a governor or similar, which will limit the shaft power to keep the speed constant. This will control the input power in a simple manner.
If you can't guarantee that your mechanical input is higher, you'll need to limit your output power in some way. I have done it where we controlled the output current via a PID feedback controller to keep the shaft speed at fixed values. But that was in a DC system, where we had a large battery to push the current into during high supply times, and draw from during lower supply times.
answered 30 mins ago
Puffafish
835111
add a comment |Â
4 Answers
4
active
oldest
votes
4 Answers
4
active
oldest
votes
active
oldest
votes
active
oldest
votes
up vote
2
down vote
accepted
Electrically
Some systems do this electrically. The generator either generates DC, or the variable-frequency AC is rectified to make DC, and then an inverted makes the desired AC frequency. Common on more modern small wind turbines.
Mechanically
Other systems are mechanically controlled to get the desired frequency. The mechanism used would be called a governor. Most simple mechanical governors are not very accurate, so this would not be good enough for a grid connected device. It is also possible to make more accurate governors which work mechanically in a similar way to the paragraph below, these are commonly used on internal combustion engines.
With Feedback
Another approach, and probably the most common is to have some form of feedback. A microcontroller monitors the frequency being generated, and adjusts the mechanical system via some form of servo to get the right frequency. For example, it could open and close a sluice gate to adjust the water flow through a turbine. A more complicated system could adjust both a sluice gate and the turbine blades to keep the correct frequency while also varying the output power.
Grid Synchronous operation
In some cases, it might not be necessary at all. If you have a small wind turbine, connected to the mains grid near a coal power station, you could just hook it up and forget about it. The huge turbines in the power station will stabilise the grid frequency, and fix the rotation speed of the wind turbine. If the wind blows harder, you'll just get more current, and a slight power factor shift. Note that as more and more wind turbines get added, the folks who run the power station will get less and less happy about this, so the grid operator will eventually ban it.
answered 36 mins ago
Jack B
9,72612136
It's probably worth mentioning doubly-fed induction machines here. They use an induction machine simultaneously as both a generator and a rotary converter to keep the output frequency constant with varying input frequencies.
– Felthry
32 mins ago
@Felthry I didn't include them because I'm not sufficiently familiar with them. Feel free to propose an edit though.
– Jack B
29 mins ago
I would, but Andy's answer already takes care of that.
– Felthry
5 mins ago
add a comment |Â
up vote
2
down vote
accepted
Electrically
Some systems do this electrically. The generator either generates DC, or the variable-frequency AC is rectified to make DC, and then an inverted makes the desired AC frequency. Common on more modern small wind turbines.
Mechanically
Other systems are mechanically controlled to get the desired frequency. The mechanism used would be called a governor. Most simple mechanical governors are not very accurate, so this would not be good enough for a grid connected device. It is also possible to make more accurate governors which work mechanically in a similar way to the paragraph below, these are commonly used on internal combustion engines.
With Feedback
Another approach, and probably the most common is to have some form of feedback. A microcontroller monitors the frequency being generated, and adjusts the mechanical system via some form of servo to get the right frequency. For example, it could open and close a sluice gate to adjust the water flow through a turbine. A more complicated system could adjust both a sluice gate and the turbine blades to keep the correct frequency while also varying the output power.
Grid Synchronous operation
In some cases, it might not be necessary at all. If you have a small wind turbine, connected to the mains grid near a coal power station, you could just hook it up and forget about it. The huge turbines in the power station will stabilise the grid frequency, and fix the rotation speed of the wind turbine. If the wind blows harder, you'll just get more current, and a slight power factor shift. Note that as more and more wind turbines get added, the folks who run the power station will get less and less happy about this, so the grid operator will eventually ban it.
answered 36 mins ago
Jack B
9,72612136
It's probably worth mentioning doubly-fed induction machines here. They use an induction machine simultaneously as both a generator and a rotary converter to keep the output frequency constant with varying input frequencies.
– Felthry
32 mins ago
@Felthry I didn't include them because I'm not sufficiently familiar with them. Feel free to propose an edit though.
– Jack B
29 mins ago
I would, but Andy's answer already takes care of that.
– Felthry
5 mins ago
add a comment |Â
up vote
2
down vote
accepted
up vote
2
down vote
accepted
Electrically
Some systems do this electrically. The generator either generates DC, or the variable-frequency AC is rectified to make DC, and then an inverted makes the desired AC frequency. Common on more modern small wind turbines.
Mechanically
Other systems are mechanically controlled to get the desired frequency. The mechanism used would be called a governor. Most simple mechanical governors are not very accurate, so this would not be good enough for a grid connected device. It is also possible to make more accurate governors which work mechanically in a similar way to the paragraph below, these are commonly used on internal combustion engines.
With Feedback
Another approach, and probably the most common is to have some form of feedback. A microcontroller monitors the frequency being generated, and adjusts the mechanical system via some form of servo to get the right frequency. For example, it could open and close a sluice gate to adjust the water flow through a turbine. A more complicated system could adjust both a sluice gate and the turbine blades to keep the correct frequency while also varying the output power.
Grid Synchronous operation
In some cases, it might not be necessary at all. If you have a small wind turbine, connected to the mains grid near a coal power station, you could just hook it up and forget about it. The huge turbines in the power station will stabilise the grid frequency, and fix the rotation speed of the wind turbine. If the wind blows harder, you'll just get more current, and a slight power factor shift. Note that as more and more wind turbines get added, the folks who run the power station will get less and less happy about this, so the grid operator will eventually ban it.
answered 36 mins ago
Jack B
9,72612136
Electrically
Some systems do this electrically. The generator either generates DC, or the variable-frequency AC is rectified to make DC, and then an inverted makes the desired AC frequency. Common on more modern small wind turbines.
Mechanically
Other systems are mechanically controlled to get the desired frequency. The mechanism used would be called a governor. Most simple mechanical governors are not very accurate, so this would not be good enough for a grid connected device. It is also possible to make more accurate governors which work mechanically in a similar way to the paragraph below, these are commonly used on internal combustion engines.
With Feedback
Another approach, and probably the most common is to have some form of feedback. A microcontroller monitors the frequency being generated, and adjusts the mechanical system via some form of servo to get the right frequency. For example, it could open and close a sluice gate to adjust the water flow through a turbine. A more complicated system could adjust both a sluice gate and the turbine blades to keep the correct frequency while also varying the output power.
Grid Synchronous operation
In some cases, it might not be necessary at all. If you have a small wind turbine, connected to the mains grid near a coal power station, you could just hook it up and forget about it. The huge turbines in the power station will stabilise the grid frequency, and fix the rotation speed of the wind turbine. If the wind blows harder, you'll just get more current, and a slight power factor shift. Note that as more and more wind turbines get added, the folks who run the power station will get less and less happy about this, so the grid operator will eventually ban it.
answered 36 mins ago
Jack B
9,72612136
edited 27 mins ago
answered 36 mins ago
Jack B
9,72612136
answered 36 mins ago
Jack B
9,72612136
answered 36 mins ago
Jack B
9,72612136
9,72612136
It's probably worth mentioning doubly-fed induction machines here. They use an induction machine simultaneously as both a generator and a rotary converter to keep the output frequency constant with varying input frequencies.
– Felthry
32 mins ago
@Felthry I didn't include them because I'm not sufficiently familiar with them. Feel free to propose an edit though.
– Jack B
29 mins ago
I would, but Andy's answer already takes care of that.
– Felthry
5 mins ago
add a comment |Â
It's probably worth mentioning doubly-fed induction machines here. They use an induction machine simultaneously as both a generator and a rotary converter to keep the output frequency constant with varying input frequencies.
– Felthry
32 mins ago
@Felthry I didn't include them because I'm not sufficiently familiar with them. Feel free to propose an edit though.
– Jack B
29 mins ago
I would, but Andy's answer already takes care of that.
– Felthry
5 mins ago
It's probably worth mentioning doubly-fed induction machines here. They use an induction machine simultaneously as both a generator and a rotary converter to keep the output frequency constant with varying input frequencies.
– Felthry
32 mins ago
It's probably worth mentioning doubly-fed induction machines here. They use an induction machine simultaneously as both a generator and a rotary converter to keep the output frequency constant with varying input frequencies.
– Felthry
32 mins ago
@Felthry I didn't include them because I'm not sufficiently familiar with them. Feel free to propose an edit though.
– Jack B
29 mins ago
@Felthry I didn't include them because I'm not sufficiently familiar with them. Feel free to propose an edit though.
– Jack B
29 mins ago
I would, but Andy's answer already takes care of that.
– Felthry
5 mins ago
I would, but Andy's answer already takes care of that.
– Felthry
5 mins ago
add a comment |Â
up vote
2
down vote
A lot of wind generators use a doubly fed induction generator (DFIG): -
They can convert power at one frequency to another frequency i.e. they can produce 50/60 Hz even though the rotor may be running too slowly. This is done by injection of an AC current into the rotor coils. The control system that acheives this may also be able to alter pitch angle of the turbine as another means of increasing or decreasing mechanical rotation speed.
For more information please read this EE answer.
answered 28 mins ago
Andy aka
233k10172397
add a comment |Â
up vote
2
down vote
A lot of wind generators use a doubly fed induction generator (DFIG): -
They can convert power at one frequency to another frequency i.e. they can produce 50/60 Hz even though the rotor may be running too slowly. This is done by injection of an AC current into the rotor coils. The control system that acheives this may also be able to alter pitch angle of the turbine as another means of increasing or decreasing mechanical rotation speed.
For more information please read this EE answer.
answered 28 mins ago
Andy aka
233k10172397
add a comment |Â
up vote
2
down vote
up vote
2
down vote
A lot of wind generators use a doubly fed induction generator (DFIG): -
They can convert power at one frequency to another frequency i.e. they can produce 50/60 Hz even though the rotor may be running too slowly. This is done by injection of an AC current into the rotor coils. The control system that acheives this may also be able to alter pitch angle of the turbine as another means of increasing or decreasing mechanical rotation speed.
For more information please read this EE answer.
answered 28 mins ago
Andy aka
233k10172397
A lot of wind generators use a doubly fed induction generator (DFIG): -
They can convert power at one frequency to another frequency i.e. they can produce 50/60 Hz even though the rotor may be running too slowly. This is done by injection of an AC current into the rotor coils. The control system that acheives this may also be able to alter pitch angle of the turbine as another means of increasing or decreasing mechanical rotation speed.
For more information please read this EE answer.
answered 28 mins ago
Andy aka
233k10172397
answered 28 mins ago
Andy aka
233k10172397
answered 28 mins ago
Andy aka
233k10172397
answered 28 mins ago
Andy aka
233k10172397
233k10172397
add a comment |Â
add a comment |Â
up vote
1
down vote
That is what a governor is for.
The mechanical version is a device that will use centrifugal force or a blower to actuate the throttle/intake to slow down the engine when the speed climbs too much.
You can make it electronic with an RPM sensor and a electronically controlled throttle/intake.
answered 43 mins ago
ratchet freak
2,4401011
add a comment |Â
up vote
1
down vote
That is what a governor is for.
The mechanical version is a device that will use centrifugal force or a blower to actuate the throttle/intake to slow down the engine when the speed climbs too much.
You can make it electronic with an RPM sensor and a electronically controlled throttle/intake.
answered 43 mins ago
ratchet freak
2,4401011
add a comment |Â
up vote
1
down vote
up vote
1
down vote
That is what a governor is for.
The mechanical version is a device that will use centrifugal force or a blower to actuate the throttle/intake to slow down the engine when the speed climbs too much.
You can make it electronic with an RPM sensor and a electronically controlled throttle/intake.
answered 43 mins ago
ratchet freak
2,4401011
That is what a governor is for.
The mechanical version is a device that will use centrifugal force or a blower to actuate the throttle/intake to slow down the engine when the speed climbs too much.
You can make it electronic with an RPM sensor and a electronically controlled throttle/intake.
answered 43 mins ago
ratchet freak
2,4401011
answered 43 mins ago
ratchet freak
2,4401011
answered 43 mins ago
ratchet freak
2,4401011
answered 43 mins ago
ratchet freak
2,4401011
2,4401011
add a comment |Â
add a comment |Â
up vote
1
down vote
In my (limited) experience of generator design, you have to look at multiple factors:
Speed of mechanical input (turbine, wheel etc)
Power of mechanical input
Output voltage
Output current
Output power (which depends on voltage and current, but you usually want to maximise this, at a peak power point)
In many cases what you want to maintain is a constant voltage output, which will vary with the electrical load; higher current would make the output drop.
In your set up, you only care about the speed of the shaft (for whatever reason that is). There are two ways to do this: control input power or control output power.
If you know that your mechanical power will always be more than the output power, you could use a governor or similar, which will limit the shaft power to keep the speed constant. This will control the input power in a simple manner.
If you can't guarantee that your mechanical input is higher, you'll need to limit your output power in some way. I have done it where we controlled the output current via a PID feedback controller to keep the shaft speed at fixed values. But that was in a DC system, where we had a large battery to push the current into during high supply times, and draw from during lower supply times.
answered 30 mins ago
Puffafish
835111
add a comment |Â
up vote
1
down vote
In my (limited) experience of generator design, you have to look at multiple factors:
Speed of mechanical input (turbine, wheel etc)
Power of mechanical input
Output voltage
Output current
Output power (which depends on voltage and current, but you usually want to maximise this, at a peak power point)
In many cases what you want to maintain is a constant voltage output, which will vary with the electrical load; higher current would make the output drop.
In your set up, you only care about the speed of the shaft (for whatever reason that is). There are two ways to do this: control input power or control output power.
If you know that your mechanical power will always be more than the output power, you could use a governor or similar, which will limit the shaft power to keep the speed constant. This will control the input power in a simple manner.
If you can't guarantee that your mechanical input is higher, you'll need to limit your output power in some way. I have done it where we controlled the output current via a PID feedback controller to keep the shaft speed at fixed values. But that was in a DC system, where we had a large battery to push the current into during high supply times, and draw from during lower supply times.
answered 30 mins ago
Puffafish
835111
add a comment |Â
up vote
1
down vote
up vote
1
down vote
In my (limited) experience of generator design, you have to look at multiple factors:
Speed of mechanical input (turbine, wheel etc)
Power of mechanical input
Output voltage
Output current
Output power (which depends on voltage and current, but you usually want to maximise this, at a peak power point)
In many cases what you want to maintain is a constant voltage output, which will vary with the electrical load; higher current would make the output drop.
In your set up, you only care about the speed of the shaft (for whatever reason that is). There are two ways to do this: control input power or control output power.
If you know that your mechanical power will always be more than the output power, you could use a governor or similar, which will limit the shaft power to keep the speed constant. This will control the input power in a simple manner.
If you can't guarantee that your mechanical input is higher, you'll need to limit your output power in some way. I have done it where we controlled the output current via a PID feedback controller to keep the shaft speed at fixed values. But that was in a DC system, where we had a large battery to push the current into during high supply times, and draw from during lower supply times.
answered 30 mins ago
Puffafish
835111
In my (limited) experience of generator design, you have to look at multiple factors:
Speed of mechanical input (turbine, wheel etc)
Power of mechanical input
Output voltage
Output current
Output power (which depends on voltage and current, but you usually want to maximise this, at a peak power point)
In many cases what you want to maintain is a constant voltage output, which will vary with the electrical load; higher current would make the output drop.
In your set up, you only care about the speed of the shaft (for whatever reason that is). There are two ways to do this: control input power or control output power.
If you know that your mechanical power will always be more than the output power, you could use a governor or similar, which will limit the shaft power to keep the speed constant. This will control the input power in a simple manner.
If you can't guarantee that your mechanical input is higher, you'll need to limit your output power in some way. I have done it where we controlled the output current via a PID feedback controller to keep the shaft speed at fixed values. But that was in a DC system, where we had a large battery to push the current into during high supply times, and draw from during lower supply times.
answered 30 mins ago
Puffafish
835111
answered 30 mins ago
Puffafish
835111
answered 30 mins ago
Puffafish
835111
answered 30 mins ago
Puffafish
835111
835111
add a comment |Â
add a comment |Â
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With some sort of throttle on the prime mover, adjusted so that power in equals power out (plus internal losses).
– Dave Tweed♦
42 mins ago
I'm pretty sure that large generators attached to mains are forced into synchronicity by the influence of all the other things attached to mains; if the generator slows down any, there would be a motor torque applied by the mains power pulling it back towards synchronous speed, and likewise if it speeds up. This is a problem in itself rather than a solution, though, because if your generator starts running as a motor it's likely to tear itself or things attached to its shaft apart; it's not made to operate like that.
– Felthry
35 mins ago