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Generator Syncing

J

Jim Rojas

Jan 1, 1970
0
Is there an electronic solution to automatically sync AC generators,
motors, or any other AC sources?

At my home I have a micro hydro setup. I have (2) 3 phase AC water pump
motors spinning backwards that each provide 240v 6amps, that I would
like to sync together. At the present time, I run them separately
running 2 different circuit breaker panels, and a set of capacitors as a
low cost line conditioner to smooth out peak surges.

I would like to parallel 2 more pumps as redundant backups in case one
of them fail. They have been running this setup for 2 years now. My grid
electric bill is down to just minimum service charges of about $17 a
month. I average 700KW a month usage.

My setup has a auto transfer switch from grid tie power to my motors and
backup genset.

Any advice would be greatly appreciated.

Thank you

Jim Rojas
 
J

Jim Rojas

Jan 1, 1970
0
Salmon said:
Are these synchronous motors? If they are induction motors, how do you
get the reactive excitation current?

Bill

Yes I believe they are synchronous motors.

Jim Rojas
 
D

Don Kelly

Jan 1, 1970
0
Yes I believe they are synchronous motors.

Jim Rojas

-----
It would be nice to know for sure- water pump motors are likely to be
induction machines- check the nameplate data- rated speed in particular.
Do they generate without the backup genset? In that case do they always
operate them with no connection to the genset (no synchronising with the
genset)? The capacitors may provide some of the reactive needs but how much
conditioning they do is unclear and such conditioning may not actually be
needed other than reactive support. More information is needed- including
the capacitor rating.

By the way 700KW/month is meaningless. I assume that you mean 700KWH a
month.
 
J

Jim Rojas

Jan 1, 1970
0
Don said:
It would be nice to know for sure- water pump motors are likely to be
induction machines- check the nameplate data- rated speed in
particular. Do they generate without the backup genset? In that case do
they always operate them with no connection to the genset (no
synchronising with the genset)? The capacitors may provide some of the
reactive needs but how much conditioning they do is unclear and such
conditioning may not actually be needed other than reactive support.
More information is needed- including the capacitor rating.

By the way 700KW/month is meaningless. I assume that you mean 700KWH a
month.

Ok. I will take a look on the nameplate tomorrow.

700KWH is correct.

Jim Rojas
 
J

Jim Rojas

Jan 1, 1970
0
Don said:
It would be nice to know for sure- water pump motors are likely to be
induction machines- check the nameplate data- rated speed in
particular. Do they generate without the backup genset? In that case do
they always operate them with no connection to the genset (no
synchronising with the genset)? The capacitors may provide some of the
reactive needs but how much conditioning they do is unclear and such
conditioning may not actually be needed other than reactive support.
More information is needed- including the capacitor rating.

By the way 700KW/month is meaningless. I assume that you mean 700KWH a
month.

I stand corrected. It is an induction motor.

The info below comes from an overseas friend who help me set it up:

The motor is 3 phase. In order to reduce it to single-phase, 3
capacitors, one 70 μF and the other 140 μF (two 70 μF capacitors wired
in parallel) were wired in a “C-2C†configuration, this process provides
excitation. 70 μF is on one phase, 140 μF is on the other, and the third
phase having none. We have plans to add a newer controller and a better
ballast load, but this will have to wait until I return to Florida in
the spring. Manually synchronizing these motors is pretty straight
forward, but I would like to do it automatically when I am away. Either
with an electronic circuit or even with a relays...either way it must be
something any homeowner can handle without too much difficulty.

Jim Rojas
 
J

Jim Rojas

Jan 1, 1970
0
Salmon said:
Jim Rojas is in over his head. I personally will not help him get into
deeper problems. He needs to hire competent help.

Bill

My expertise is in electronic security. This is why I am asking for some
help.

Thank you

Jim Rojas
 
J

James Sweet

Jan 1, 1970
0
Salmon said:
Are these synchronous motors? If they are induction motors, how do you
get the reactive excitation current?

Bill


Induction motors can be used as generators, sometimes there's enough
residual magnetism to get them going. I recall reading that if you load
them past a certain point, the output just falls to zero and you have to
start over. I've never actually tried using one for that myself though.
I don't think they're very efficient generators, but they are cheap.
 
J

Jim Rojas

Jan 1, 1970
0
Salmon said:
Jim Rojas is in over his head. I personally will not help him get into
deeper problems. He needs to hire competent help.

Bill

The county I live in has a 5KW per single motor size limit before a
laundry list of special permitting, engineers drawings, and inspections
are required. They do allow paralleling of motors, up to 4, as long as
they are all under 5KW each. I really need 10-15KW in the summer months.
Everything in my home is electric. A 10+KW motor can easily weigh in at
a couple of hundred pounds, to a ton. If a motor goes bad, I want to be
able to replace it easily in a day, and not rent a bobcat, and start a
huge permitting issue just on motor change out.

It took me 3 years, and many letters to get the county to allow me to
use water to power the motor. Once they saw that the diverted water
quickly worked its way back into the water table, without any pollution,
they signed off on it.

Jim Rojas
 
J

Jim Rojas

Jan 1, 1970
0
James said:
Induction motors can be used as generators, sometimes there's enough
residual magnetism to get them going. I recall reading that if you load
them past a certain point, the output just falls to zero and you have to
start over. I've never actually tried using one for that myself though.
I don't think they're very efficient generators, but they are cheap.

This looks like what I need.

http://www.woodward.com/pdf/ic/82383.pdf

Thank you all for your assistance.

Jim Rojas
 
J

Jim Rojas

Jan 1, 1970
0
James said:
Induction motors can be used as generators, sometimes there's enough
residual magnetism to get them going. I recall reading that if you load
them past a certain point, the output just falls to zero and you have to
start over. I've never actually tried using one for that myself though.
I don't think they're very efficient generators, but they are cheap.

I found this one as well...far less complicated and far less to purchase.

http://www.made-in-china.com/showro...rator-Automatic-Synchronizer-SY-SC-202X-.html

Jim Rojas
 
J

James Sweet

Jan 1, 1970
0
The county I live in has a 5KW per single motor size limit before a
laundry list of special permitting, engineers drawings, and inspections
are required. They do allow paralleling of motors, up to 4, as long as
they are all under 5KW each. I really need 10-15KW in the summer months.
Everything in my home is electric. A 10+KW motor can easily weigh in at
a couple of hundred pounds, to a ton. If a motor goes bad, I want to be
able to replace it easily in a day, and not rent a bobcat, and start a
huge permitting issue just on motor change out.

It took me 3 years, and many letters to get the county to allow me to
use water to power the motor. Once they saw that the diverted water
quickly worked its way back into the water table, without any pollution,
they signed off on it.

Jim Rojas



I sure wish there was something of that nature around me, there's no
flowing water anywhere on my property though.

Can you just wire them up in parallel? Certainly connecting a large
generator out of sync to the grid is disastrous, but something of this
nature I would have thought would sync up on its own just by switching
it in, they are motors afterall.
 
J

Jim Rojas

Jan 1, 1970
0
James said:
I sure wish there was something of that nature around me, there's no
flowing water anywhere on my property though.

Can you just wire them up in parallel? Certainly connecting a large
generator out of sync to the grid is disastrous, but something of this
nature I would have thought would sync up on its own just by switching
it in, they are motors afterall.

I am no expert. But just paralleling AC motors would probably break the
armature on one or both. I can also see the motor coils frying. You can
easily parallel with DC motors. But DC motors require expensive
controllers and inverters which makes it alot less appealing dollar wise.

Jim Rojas
 
J

James Sweet

Jan 1, 1970
0
I am no expert. But just paralleling AC motors would probably break the
armature on one or both. I can also see the motor coils frying. You can
easily parallel with DC motors. But DC motors require expensive
controllers and inverters which makes it alot less appealing dollar wise.

Jim Rojas


It could be a real problem if the generators were driven by something
with a lot of torque and rotational mass, like a reciprocating engine,
but I would think a generator in that power range driven by a small
hydro turbine would not have any problems. Remember that in normal use
they are abruptly connected to the AC line when used as a motor, and
they spin up to speed on their own driving a load. The only difference
here is that the motor is already spinning when you connect it to the
grid. You certainly won't fry the coils.
 
D

daestrom

Jan 1, 1970
0
Jim said:
I am no expert. But just paralleling AC motors would probably break the
armature on one or both. I can also see the motor coils frying. You can
easily parallel with DC motors. But DC motors require expensive
controllers and inverters which makes it alot less appealing dollar wise.

What you're saying about AC synchronous generators could be true,
depending on the sizes and such.

But if I understand you so far, these are really induction generators
(AC induction motors driven at greater than synchronous speed).
Induction generators don't 'lock' in to synch with the running supply.

The nature of induction generators can make operating them in parallel a
bit tricky as well. When unloaded, the AC output is very close in
frequency to the synchronous output (f= N*P/120 where N is RPM and P is
number of poles). But as they are loaded, the speed must be raised if
you want to maintain a constant frequency output. This is because the %
slip between output frequency and rotor speed rises with load.

Because induction generators don't have their own internal excitation,
you might find it easiest to connect the incoming machine by just
running it at synchronous speed without any capacitors and connect it to
the line. This is equivalent to connecting an induction motor across
the line when it's already spinning at rated speed. No large surge
currents.

After it's on the line, then connect the capacitors to provide the
excitation needed.

daestrom
 
J

Jim Rojas

Jan 1, 1970
0
daestrom said:
What you're saying about AC synchronous generators could be true,
depending on the sizes and such.

But if I understand you so far, these are really induction generators
(AC induction motors driven at greater than synchronous speed).
Induction generators don't 'lock' in to synch with the running supply.

The nature of induction generators can make operating them in parallel a
bit tricky as well. When unloaded, the AC output is very close in
frequency to the synchronous output (f= N*P/120 where N is RPM and P is
number of poles). But as they are loaded, the speed must be raised if
you want to maintain a constant frequency output. This is because the %
slip between output frequency and rotor speed rises with load.

Because induction generators don't have their own internal excitation,
you might find it easiest to connect the incoming machine by just
running it at synchronous speed without any capacitors and connect it to
the line. This is equivalent to connecting an induction motor across
the line when it's already spinning at rated speed. No large surge
currents.

After it's on the line, then connect the capacitors to provide the
excitation needed.

daestrom

Thank you for the advice.

Jim Rojas
 
D

Don Kelly

Jan 1, 1970
0
Jim Rojas said:
Thank you for the advice.

Jim Rojas
As Daestrom indicates, induction motors are easy and synchronization is not
needed. However, for best operation, they should be connected to the system
as the system must provide reactive (and this will be appreciable).
With the system connection, the system dictates the frequency independently
of the speed of the motor but, if it can't supply the needed reactive, the
voltage will be low. Capacitors in parallel will help provide this
reactive. Parallel operation shouldn't be a problem if there is sufficient
capacity, system + capacitors to supply the reactive.
In more remote parts of Scotland, induction motors have been used in that
way.
Daestrom's statements appear to be based on stand-alone setups and there
could be problems there as you then do get into control of the sources
driving the two motors to try and maintain the same frequency (if not
quite the same, there will be some messy circulating currents as one motor
may try to accelerate the other until they are at the same speed This may
not fit the conditions imposed by the prime movers and water flow).
In your case it appears that you do have a standby generator (substitute for
the grid system and governed to control frequency which can provide the
necessary frequency control and take care of excitation and load reactive
with the assistance of parallel capacitors. How much? As a rough measure-
the no load current and KVA (volt-amps) which would be near 50% of the
motor rating.

In any case the more information available - the better an answer can be.
For example, you don't specify how much of your load is single phase nor the
rating of your backup generator. What is the maximum power load that you
want to deal with? Do you run the two induction generators independently of
this backup generator? If so, how well do they hold frequency? It all
boils down to what you actually have and how you are using this at present.
 
D

Don Kelly

Jan 1, 1970
0
It is intended for synchronous machines- both phase (speed of prime mover)
and voltage control. On the basis of the description given- don't bother
wasting your money.

You don't have either when dealing with induction motors. If you are
connected to the grid, and they allow it, then you can simply open the gates
to let the water run and then connect the induction machine to the grid. The
amount of power produced is at grid frequency and is dependent on the "slip
speed" of the machine. This also means that excess is fed back to the grid.
For example, a motor rated at 10KW (input) at 5% slip (say 1710 rpm for a 60
Hz 4 pole machine) will produce something near (but under) 10KW at 1890
rpm. What you actually get is dependent on the prime mover as well as the
motor/generator used.
-
Don Kelly
cross out to reply
 
A

Archimedes' Lever

Jan 1, 1970
0
I remember having to do that manually on our emergency generators when I
first started work. Watch the syncroscope and operate the breaker at about
"5 to the hour". This allows time for the breaker to actually close. I
can't remember the output of the generators but rated in 100s of kW The
motive power was an "English Electric" 6L marine diesel, running at
375rpm; compressed air start.

Speed of generator 2 was always adjusted such that the syncroscope was
rotating slowly clockwise.


Which is why it ran at 375, instead of 360.
 
D

daestrom

Jan 1, 1970
0
Stuart said:
I remember having to do that manually on our emergency generators when I
first started work. Watch the syncroscope and operate the breaker at about
"5 to the hour". This allows time for the breaker to actually close.

You may find it interesting, but this is *exactly* how a 1000 MW nuclear
plant (BWR) syncs onto the grid as well.

We use the governor in speed-control mode to get the 'scope going very
slowly in the 'fast' direction (clockwise). And we wait a little closer
to 'midnight', but the basic steps are the same.

Then we run the governor 'up out of the way' and let the pressure
controls for the plant control the loading. (in BWR's the turbine is
slaved to follow reactor power instead of like PWR's where it's the
other way 'round)

We do have 'synch-check' relays, that interlock the closing circuit, so
that if an operator screws up, he *can't* close the breaker more than a
few degrees out of phase.

daestrom
P.S. But these are synchronous generators, not the induction generators
the OP mentioned.
 
D

daestrom

Jan 1, 1970
0
Archimedes' Lever said:
Which is why it ran at 375, instead of 360.

Nah, that don't sound right. If synchronous speed were 360, that would
be a 20 pole machine. At 375, that would be 62.5 Hz instead of 60. You
can't parallel with 2.5 Hz difference. Most synchroscopes won't even
rotate continuously with that much frequency difference, they just
'stutter'/wiggle back and forth.

To get the 'scope to rotate 'slowly in the 'fast' direction' takes only
about 0.2 Hz or less difference.

More likely it ran at 375 because it was a 16 pole *50* Hz machine
('English Electric' might be British).

daestrom
 
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