DIY induction motor as generator for cleaner power?

Guest
More generator stuff. Reading about squirrel cage induction motors I
find that induction motors can be used as generators if driven faster
than what its synchronous speed would be if it could attain that
speed. If connected to ac at the same frequency it is designed to run
at it will produce ac at that same frequency no matter how fast it is
spinning. Apparently some alternative energy folks use this method to
feed power back into the grid and reduce their electricity bill. An
advantage of this is that if the grid power fails the generator also
quits producing power and so cannot dangerously energize the grid. So
I was wondering if a practical generator could be made if an induction
motor was connected to a low wattage clean ac power source, such as a
true sine wave inverter.
Thanks,
Eric
 
On Wed, 20 Jan 2016 11:27:10 -0800, etpm wrote:

More generator stuff. Reading about squirrel cage induction motors I
find that induction motors can be used as generators if driven faster
than what its synchronous speed would be if it could attain that speed.
If connected to ac at the same frequency it is designed to run at it
will produce ac at that same frequency no matter how fast it is
spinning. Apparently some alternative energy folks use this method to
feed power back into the grid and reduce their electricity bill. An
advantage of this is that if the grid power fails the generator also
quits producing power and so cannot dangerously energize the grid. So I
was wondering if a practical generator could be made if an induction
motor was connected to a low wattage clean ac power source, such as a
true sine wave inverter.
Thanks,
Eric
Click to expand...

Yes and no.

An inductive machine hooked up and driven that way will look like either
a capacitor or an inductor (I can't remember which!), and it will produce
power proportional to the drive torque.

So your little clean sine wave inverter will, first, need to have enough
current capacity to drive the reactive VARs to the inductive machine, and
second, would need to have somewhere to put all the excess energy that
would be getting stuffed onto the line any time the mechanical input
power exceeded the electric power being used.

I suspect that if you just took a little 1000W Honda generator and hooked
it up to a 10 horsepower motor spinning at 3800 RPM that the best you
could hope for would be a blown circuit breaker in the generator and no
useful power.

Basically, turning an inductive machine at faster than the synchronous
RPM works when it's connected to a big grid, but when such critters start
dominating the grid then things won't go so well.

You could come up with some exotic VFD that would back-flow power to the
electric line, but one way or another you'd need herky enough electronics
to take the raw stuff coming out of the generator and turn it into
something at 120V, 60Hz.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
 
On Wednesday, January 20, 2016 at 5:33:23 PM UTC-5, Tim Wescott wrote:
On Wed, 20 Jan 2016 11:27:10 -0800, etpm wrote:

More generator stuff. Reading about squirrel cage induction motors I
find that induction motors can be used as generators if driven faster
than what its synchronous speed would be if it could attain that speed.
If connected to ac at the same frequency it is designed to run at it
will produce ac at that same frequency no matter how fast it is
spinning. Apparently some alternative energy folks use this method to
feed power back into the grid and reduce their electricity bill. An
advantage of this is that if the grid power fails the generator also
quits producing power and so cannot dangerously energize the grid. So I
was wondering if a practical generator could be made if an induction
motor was connected to a low wattage clean ac power source, such as a
true sine wave inverter.
Thanks,
Eric

Yes and no.

An inductive machine hooked up and driven that way will look like either
a capacitor or an inductor (I can't remember which!), and it will produce
power proportional to the drive torque.
Click to expand...

I think it looks capacitive... At least that's what I recall from a Helium
liqufier manual.. I ran it for a while back in grad school.
The brake on the expansion engine was such a motor/ generator that sent power
back into the grid.

George H.
So your little clean sine wave inverter will, first, need to have enough
current capacity to drive the reactive VARs to the inductive machine, and
second, would need to have somewhere to put all the excess energy that
would be getting stuffed onto the line any time the mechanical input
power exceeded the electric power being used.

I suspect that if you just took a little 1000W Honda generator and hooked
it up to a 10 horsepower motor spinning at 3800 RPM that the best you
could hope for would be a blown circuit breaker in the generator and no
useful power.

Basically, turning an inductive machine at faster than the synchronous
RPM works when it's connected to a big grid, but when such critters start
dominating the grid then things won't go so well.

You could come up with some exotic VFD that would back-flow power to the
electric line, but one way or another you'd need herky enough electronics
to take the raw stuff coming out of the generator and turn it into
something at 120V, 60Hz.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
Click to expand...
 
On Thu, 21 Jan 2016 06:35:46 -0800 (PST), George Herold
<gherold@teachspin.com> wrote:

On Wednesday, January 20, 2016 at 5:33:23 PM UTC-5, Tim Wescott wrote:
On Wed, 20 Jan 2016 11:27:10 -0800, etpm wrote:

More generator stuff. Reading about squirrel cage induction motors I
find that induction motors can be used as generators if driven faster
than what its synchronous speed would be if it could attain that speed.
If connected to ac at the same frequency it is designed to run at it
will produce ac at that same frequency no matter how fast it is
spinning. Apparently some alternative energy folks use this method to
feed power back into the grid and reduce their electricity bill. An
advantage of this is that if the grid power fails the generator also
quits producing power and so cannot dangerously energize the grid. So I
was wondering if a practical generator could be made if an induction
motor was connected to a low wattage clean ac power source, such as a
true sine wave inverter.
Thanks,
Eric

Yes and no.

An inductive machine hooked up and driven that way will look like either
a capacitor or an inductor (I can't remember which!), and it will produce
power proportional to the drive torque.

I think it looks capacitive... At least that's what I recall from a Helium
liqufier manual.. I ran it for a while back in grad school.
The brake on the expansion engine was such a motor/ generator that sent power
back into the grid.

George H.
Click to expand...

Many years ago I worked for Cadillac Motor Car in Detroit,
who had their own on-site power plant. The coolest thing
there was a "rotating capacitor", which was an enormous
slow-turning flywheel maybe 20 feet in diameter, axle at
floor level so the bottom half of the wheel went below the
floor.

They used this to get a better rate from the local utility
company, by making the largely-inductive load of the factory
look neutral or capacitive to the utility.

Best regards,


Bob Masta

DAQARTA v8.00
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Scope, Spectrum, Spectrogram, Sound Level Meter
Frequency Counter, Pitch Track, Pitch-to-MIDI
FREE 8-channel Signal Generator, DaqMusiq generator
Science with your sound card!
 
On Fri, 22 Jan 2016 13:28:15 +0000, Bob Masta wrote:

On Thu, 21 Jan 2016 06:35:46 -0800 (PST), George Herold
gherold@teachspin.com> wrote:

On Wednesday, January 20, 2016 at 5:33:23 PM UTC-5, Tim Wescott wrote:
On Wed, 20 Jan 2016 11:27:10 -0800, etpm wrote:

More generator stuff. Reading about squirrel cage induction motors I
find that induction motors can be used as generators if driven
faster than what its synchronous speed would be if it could attain
that speed.
If connected to ac at the same frequency it is designed to run at it
will produce ac at that same frequency no matter how fast it is
spinning. Apparently some alternative energy folks use this method
to feed power back into the grid and reduce their electricity bill.
An advantage of this is that if the grid power fails the generator
also quits producing power and so cannot dangerously energize the
grid. So I was wondering if a practical generator could be made if
an induction motor was connected to a low wattage clean ac power
source, such as a true sine wave inverter.
Thanks,
Eric

Yes and no.

An inductive machine hooked up and driven that way will look like
either a capacitor or an inductor (I can't remember which!), and it
will produce power proportional to the drive torque.

I think it looks capacitive... At least that's what I recall from a
Helium liqufier manual.. I ran it for a while back in grad school.
The brake on the expansion engine was such a motor/ generator that sent
power back into the grid.

George H.

Many years ago I worked for Cadillac Motor Car in Detroit, who had their
own on-site power plant. The coolest thing there was a "rotating
capacitor", which was an enormous slow-turning flywheel maybe 20 feet in
diameter, axle at floor level so the bottom half of the wheel went below
the floor.

They used this to get a better rate from the local utility company, by
making the largely-inductive load of the factory look neutral or
capacitive to the utility.
Click to expand...

If you have a synchronous machine with a variable field you can trim
whether the thing looks inductive, capacitive, or neutral by trimming the
intensity on the field winding.

So it could be done with "just" a honkin' big synchronous motor and a
flywheel. I don't know if devices were made specifically for the task,
though.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
 
On Fri, 22 Jan 2016 14:39:42 -0600, Tim Wescott
<seemywebsite@myfooter.really> wrote:

On Fri, 22 Jan 2016 13:28:15 +0000, Bob Masta wrote:

On Thu, 21 Jan 2016 06:35:46 -0800 (PST), George Herold
gherold@teachspin.com> wrote:

On Wednesday, January 20, 2016 at 5:33:23 PM UTC-5, Tim Wescott wrote:
On Wed, 20 Jan 2016 11:27:10 -0800, etpm wrote:

More generator stuff. Reading about squirrel cage induction motors I
find that induction motors can be used as generators if driven
faster than what its synchronous speed would be if it could attain
that speed.
If connected to ac at the same frequency it is designed to run at it
will produce ac at that same frequency no matter how fast it is
spinning. Apparently some alternative energy folks use this method
to feed power back into the grid and reduce their electricity bill.
An advantage of this is that if the grid power fails the generator
also quits producing power and so cannot dangerously energize the
grid. So I was wondering if a practical generator could be made if
an induction motor was connected to a low wattage clean ac power
source, such as a true sine wave inverter.
Thanks,
Eric

Yes and no.

An inductive machine hooked up and driven that way will look like
either a capacitor or an inductor (I can't remember which!), and it
will produce power proportional to the drive torque.

I think it looks capacitive... At least that's what I recall from a
Helium liqufier manual.. I ran it for a while back in grad school.
The brake on the expansion engine was such a motor/ generator that sent
power back into the grid.

George H.

Many years ago I worked for Cadillac Motor Car in Detroit, who had their
own on-site power plant. The coolest thing there was a "rotating
capacitor", which was an enormous slow-turning flywheel maybe 20 feet in
diameter, axle at floor level so the bottom half of the wheel went below
the floor.

They used this to get a better rate from the local utility company, by
making the largely-inductive load of the factory look neutral or
capacitive to the utility.

If you have a synchronous machine with a variable field you can trim
whether the thing looks inductive, capacitive, or neutral by trimming the
intensity on the field winding.

So it could be done with "just" a honkin' big synchronous motor and a
flywheel. I don't know if devices were made specifically for the task,
though.
Click to expand...

As far as I know this was specifically for PFC. (They also
had a separate conventional coal-fired generator for power
backup.) Back then, if not still today, factories almost
always presented inductive loads, and there were no
industries or customers that provided loads that were
naturally capacitive. So the utility company was happy to
offer reduced rates to get PFC.

Best regards,


Bob Masta

DAQARTA v8.00
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Scope, Spectrum, Spectrogram, Sound Level Meter
Frequency Counter, Pitch Track, Pitch-to-MIDI
FREE 8-channel Signal Generator, DaqMusiq generator
Science with your sound card!
 
Tim Wescott <seemywebsite@myfooter.really> wrote:
On Fri, 22 Jan 2016 13:28:15 +0000, Bob Masta wrote:

On Thu, 21 Jan 2016 06:35:46 -0800 (PST), George Herold
gherold@teachspin.com> wrote:

On Wednesday, January 20, 2016 at 5:33:23 PM UTC-5, Tim Wescott wrote:
On Wed, 20 Jan 2016 11:27:10 -0800, etpm wrote:

More generator stuff. Reading about squirrel cage induction motors I
find that induction motors can be used as generators if driven
faster than what its synchronous speed would be if it could attain
that speed.
If connected to ac at the same frequency it is designed to run at it
will produce ac at that same frequency no matter how fast it is
spinning. Apparently some alternative energy folks use this method
to feed power back into the grid and reduce their electricity bill.
An advantage of this is that if the grid power fails the generator
also quits producing power and so cannot dangerously energize the
grid. So I was wondering if a practical generator could be made if
an induction motor was connected to a low wattage clean ac power
source, such as a true sine wave inverter.
Thanks,
Eric

Yes and no.

An inductive machine hooked up and driven that way will look like
either a capacitor or an inductor (I can't remember which!), and it
will produce power proportional to the drive torque.

I think it looks capacitive... At least that's what I recall from a
Helium liqufier manual.. I ran it for a while back in grad school.
The brake on the expansion engine was such a motor/ generator that sent
power back into the grid.

George H.

Many years ago I worked for Cadillac Motor Car in Detroit, who had their
own on-site power plant. The coolest thing there was a "rotating
capacitor", which was an enormous slow-turning flywheel maybe 20 feet in
diameter, axle at floor level so the bottom half of the wheel went below
the floor.

They used this to get a better rate from the local utility company, by
making the largely-inductive load of the factory look neutral or
capacitive to the utility.

If you have a synchronous machine with a variable field you can trim
whether the thing looks inductive, capacitive, or neutral by trimming the
intensity on the field winding.

So it could be done with "just" a honkin' big synchronous motor and a
flywheel. I don't know if devices were made specifically for the task,
though.
Click to expand...

Could be a device to guarantee power when switching power sources to the
plant as well. There's alot energy in a large flywheel.

They make "small" as in not 20 foot diameter inertial UPS devices just for
this purpose- a cheap way to store less than a minute of power. If you
lose even a cycle or two of power, gas discharge lighting shuts off and
has to cool for x minutes to restart. that's a showstopper in large
factory.
 
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