|
Home > Archive > Electrical Engineering > July 2006 > generators
You are viewing an archived Text-only version of the thread.
To view this thread in it's original format and/or if you want to reply to
this thread please [click here]
|
|
|
| I have two 650 w 240v generators i want to use simultaneously, is this
as simple as it sounds, just wiring two output cables into one socket ?
| |
| J. B. Wood 2006-07-07, 1:25 pm |
| In article <1152272306.513899.82330@s53g2000cws.googlegroups.com>, "Motor"
<tadworth178@hotmail.com> wrote:
> I have two 650 w 240v generators i want to use simultaneously, is this
> as simple as it sounds, just wiring two output cables into one socket ?
Hello, and no. Assuming we're talking about two gasoline/diesel
engine-driven A.C. generators, you can't wire their outputs in parallel
unless the equipments are operating at the same frequency (both engines
operating at the same rpm) and have output voltages that are of equal
amplitude and in phase. Even if you could manually set-up these
conditions, the sets would quickly drift out-of-sync. IOW, auxiliary
control circuits are required to provide this capability. Some gensets
have the capability built-in and all you have to do is connect a special
synchronizing cable between the two sets. Sincerely,
John Wood (Code 5550) e-mail: wood@itd.nrl.navy.mil
Naval Research Laboratory
4555 Overlook Avenue, SW
Washington, DC 20375-5337
| |
|
| Hello disaster.
"Motor" <tadworth178@hotmail.com> wrote in message
news:1152272306.513899.82330@s53g2000cws.googlegroups.com...
I have two 650 w 240v generators i want to use simultaneously, is this
as simple as it sounds, just wiring two output cables into one socket ?
| |
| Member, Takoma Park Volunteer Fire Department 2006-07-08, 3:25 am |
| Motor wrote:
> I have two 650 w 240v generators i want to use simultaneously, is this
> as simple as it sounds, just wiring two output cables into one socket ?
>
If they were really generators the answer might be yes but as they are
more likely to be alternators then the answer is no. Is the current
that these two units provide AC or DC?
--
Tom Horne
"This alternating current stuff is just a fad. It is much too dangerous
for general use." Thomas Alva Edison
| |
| VWWall 2006-07-08, 3:25 am |
| Motor wrote:
> I have two 650 w 240v generators i want to use simultaneously, is this
> as simple as it sounds, just wiring two output cables into one socket ?
>
You need what is called an optical isolator. Just wire half the lights
to one unit and half to the other.
--
Virg Wall, PE
| |
| gfretwell@aol.com 2006-07-08, 3:25 am |
| On 7 Jul 2006 04:38:26 -0700, "Motor" <tadworth178@hotmail.com> wrote:
>I have two 650 w 240v generators i want to use simultaneously, is this
>as simple as it sounds, just wiring two output cables into one socket ?
If you can ever get them in sync they will tend to hold each other in
step but I am not really sure how you do that. I suppose if you had
some large resistive load that you could connect between them, with
the other phase conductors connected it would end up pulling them
together. Once the voltage across the load dropped to zero you could
connect them.
| |
| Palindr☻me 2006-07-08, 3:25 am |
| VWWall wrote:
> Motor wrote:
>
> You need what is called an optical isolator. Just wire half the lights
> to one unit and half to the other.
>
LOL
Oh, that brightened a dull morning..
--
Sue
| |
| daestrom 2006-07-08, 9:25 am |
|
<gfretwell@aol.com> wrote in message
news:vagua2dcm99htefs4ovpf0dlfh34e15j3h@4ax.com...
> On 7 Jul 2006 04:38:26 -0700, "Motor" <tadworth178@hotmail.com> wrote:
>
>
> If you can ever get them in sync they will tend to hold each other in
> step but I am not really sure how you do that. I suppose if you had
> some large resistive load that you could connect between them, with
> the other phase conductors connected it would end up pulling them
> together. Once the voltage across the load dropped to zero you could
> connect them.
>
If you have individual control of the governors and voltage regulators, all
you really need is a couple of light-bulbs.
If the two units are separated by a single, double-pole switch; connect one
light bulb from line to load side of one pole, and another light-bulb from
line to load side of the other pole. With both units running at *nearly*
the same speed, the light-bulbs will each 'see' 240V when the two generators
are 180 degrees out of phase and 0V when they are 0 degrees out of phase
(i.e. in synch).
Adjust the unloaded unit's governor so the bulbs are rising/falling in
brightness at a slow pace and shut the disconnect 'midway through the period
of darkness'. Or, install a voltmeter across one of the two bulbs and wait
for 0VAC.
Of course, now that they are paralleled, you have the bigger issue of
keeping them paralleled and sharing the loading (both real and reactive).
We could write a couple of chapters about governor droop settings, voltage
regulator droop settings, instrumentation to monitor real and reactive load
sharing, reactive compensation circuits, unit protection schemes, etc...
etc... etc...
Getting them in synch and paralleled, that's the easy part. As Paul Harvey
might say, "It's the rest of the story...."
daestrom
| |
| Rheilly Phoull 2006-07-08, 9:25 am |
| daestrom wrote:
> <gfretwell@aol.com> wrote in message
> news:vagua2dcm99htefs4ovpf0dlfh34e15j3h@4ax.com...
>
> If you have individual control of the governors and voltage
> regulators, all you really need is a couple of light-bulbs.
>
> If the two units are separated by a single, double-pole switch;
> connect one light bulb from line to load side of one pole, and
> another light-bulb from line to load side of the other pole. With
> both units running at *nearly* the same speed, the light-bulbs will
> each 'see' 240V when the two generators are 180 degrees out of phase
> and 0V when they are 0 degrees out of phase (i.e. in synch).
>
> Adjust the unloaded unit's governor so the bulbs are rising/falling in
> brightness at a slow pace and shut the disconnect 'midway through the
> period of darkness'. Or, install a voltmeter across one of the two
> bulbs and wait for 0VAC.
>
>
> Of course, now that they are paralleled, you have the bigger issue of
> keeping them paralleled and sharing the loading (both real and
> reactive). We could write a couple of chapters about governor droop
> settings, voltage regulator droop settings, instrumentation to
> monitor real and reactive load sharing, reactive compensation
> circuits, unit protection schemes, etc... etc... etc...
>
> Getting them in synch and paralleled, that's the easy part. As Paul
> Harvey might say, "It's the rest of the story...."
>
> daestrom
Sure is !!
--
Cheers ......... Rheilly P
Where theres a will, I want to be in it.
| |
|
| These two gensets are ac petrol driven units, that i would hope to run
a 1200 w saw table ( commutator motor) from.
Rheilly Phoull wrote:
> daestrom wrote:
>
> Sure is !!
> --
>
> Cheers ......... Rheilly P
>
> Where theres a will, I want to be in it.
| |
| daestrom 2006-07-11, 8:25 pm |
|
"Motor" <tadworth178@hotmail.com> wrote in message
news:1152611557.589366.129860@35g2000cwc.googlegroups.com...
> These two gensets are ac petrol driven units, that i would hope to run
> a 1200 w saw table ( commutator motor) from.
Okay, the *short*, *short* answer.
NO!!
daestrom
| |
| John G 2006-07-12, 3:25 am |
|
"daestrom" <daestrom@NO_SPAM_HEREtwcny.rr.com> wrote in message
news:nrXsg.84873$3B.52635@twister.nyroc.rr.com...
>
> "Motor" <tadworth178@hotmail.com> wrote in message
> news:1152611557.589366.129860@35g2000cwc.googlegroups.com...
>
> Okay, the *short*, *short* answer.
>
> NO!!
>
> daestrom
The real *short* answer may be a *Short(Circuit)* if things go just
slightly wrong.
--
John G
Wot's Your Real Problem?
| |
|
| There's no such thing as ' NO ' in my book, i'm interested to know why.
John G wrote:
> "daestrom" <daestrom@NO_SPAM_HEREtwcny.rr.com> wrote in message
> news:nrXsg.84873$3B.52635@twister.nyroc.rr.com...
>
>
> The real *short* answer may be a *Short(Circuit)* if things go just
> slightly wrong.
> --
> John G
>
> Wot's Your Real Problem?
| |
| daestrom 2006-07-12, 5:25 pm |
|
"Motor" <tadworth178@hotmail.com> wrote in message
news:1152702317.598794.84560@75g2000cwc.googlegroups.com...
> There's no such thing as ' NO ' in my book, i'm interested to know why.
I discussed some of it in a previous post. Did you read it? Here's the
long answer....
In order for the two generators to be connected together, they must both
reach the maximum positive voltage at the same instant. They must also
reach their maximum negative voltage at the same instant. This is called
being 'in synch' (short for operating in synchronism with each other).
So first, you have to hook up some 'instruments' to figure out exactly when
the two are 'in-synch' in order to connect them together. If you screw this
up and connect them when one generator is at its maximum positive part of
the sine wave, and the other is at its maximum negative point, you have 240V
of the two generators and nothing but copper wire between them. Massive
amounts of current, sparks, 'magic smoke leaking out'.
But even once you have them 'in sync' and connected together, you have
another set of problems. What if one generator's maximum positive voltage
is just a little bit higher than the other? Generators designed to be in
parallel have a special circuit built into their voltage regulators to
handle this situation (it's called a 'reactive droop' circuit). If your
machines don't have one, then any mismatch in the voltages between the two
machines results in 'circulating currents'. Those are currents flowing out
of one machine and into the other. They too can reach very high values,
overheat the windings and cause the 'magic smoke' to leak out.
Next, even if you get the voltage regulators to work together and avoid
circulating currents, you next have to look at the way that the load is
shared between the two machines. What is there to keep one machine from
supplying all the real power to the load, and the other machine to just sit
there idling? Or worse, what keeps one machine from supplying power into
the other machine and actually turning it into a motor? The governors of
the two machines prevent this if they are set up right. By adjusting the
governors of both machines to deliberately slow down the engine *slightly*
when there is more load on the generator. So if they started out equally
sharing the load and some fluke of nature caused one to assume a little more
load, its governor would slow its machine down *very slightly* and that
would cause some of the load to be shifted from itself over to the other
machine. This adjustment is called 'speed droop' and its important that
both machines have comparable settings.
Now, do your two gensets have reactive droop circuits in the voltage
regulators to prevent circulating currents? Almost certainly not. Do your
two gensets have governors that are calibrated and adjusted to provide the
same amount of speed droop on the two machines? Probably not.
A few gensets out there are built to be operated in parallel. The Honda EU
series is one that comes to mind. But most gensets this size are designed
as backup power for some small number of loads. *Not* for parallel
operation as a generating unit.
daestrom
| |
|
| Thank you sir, i'm getting it now.
daestrom wrote:
> "Motor" <tadworth178@hotmail.com> wrote in message
> news:1152702317.598794.84560@75g2000cwc.googlegroups.com...
>
> I discussed some of it in a previous post. Did you read it? Here's the
> long answer....
>
> In order for the two generators to be connected together, they must both
> reach the maximum positive voltage at the same instant. They must also
> reach their maximum negative voltage at the same instant. This is called
> being 'in synch' (short for operating in synchronism with each other).
>
> So first, you have to hook up some 'instruments' to figure out exactly when
> the two are 'in-synch' in order to connect them together. If you screw this
> up and connect them when one generator is at its maximum positive part of
> the sine wave, and the other is at its maximum negative point, you have 240V
> of the two generators and nothing but copper wire between them. Massive
> amounts of current, sparks, 'magic smoke leaking out'.
>
> But even once you have them 'in sync' and connected together, you have
> another set of problems. What if one generator's maximum positive voltage
> is just a little bit higher than the other? Generators designed to be in
> parallel have a special circuit built into their voltage regulators to
> handle this situation (it's called a 'reactive droop' circuit). If your
> machines don't have one, then any mismatch in the voltages between the two
> machines results in 'circulating currents'. Those are currents flowing out
> of one machine and into the other. They too can reach very high values,
> overheat the windings and cause the 'magic smoke' to leak out.
>
> Next, even if you get the voltage regulators to work together and avoid
> circulating currents, you next have to look at the way that the load is
> shared between the two machines. What is there to keep one machine from
> supplying all the real power to the load, and the other machine to just sit
> there idling? Or worse, what keeps one machine from supplying power into
> the other machine and actually turning it into a motor? The governors of
> the two machines prevent this if they are set up right. By adjusting the
> governors of both machines to deliberately slow down the engine *slightly*
> when there is more load on the generator. So if they started out equally
> sharing the load and some fluke of nature caused one to assume a little more
> load, its governor would slow its machine down *very slightly* and that
> would cause some of the load to be shifted from itself over to the other
> machine. This adjustment is called 'speed droop' and its important that
> both machines have comparable settings.
>
> Now, do your two gensets have reactive droop circuits in the voltage
> regulators to prevent circulating currents? Almost certainly not. Do your
> two gensets have governors that are calibrated and adjusted to provide the
> same amount of speed droop on the two machines? Probably not.
>
> A few gensets out there are built to be operated in parallel. The Honda EU
> series is one that comes to mind. But most gensets this size are designed
> as backup power for some small number of loads. *Not* for parallel
> operation as a generating unit.
>
> daestrom
|
|
|
|
|