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'[OT]:how are hydroelectric power stations synchron'
2011\05\08@005626 by Justin Richards

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The question has come up regarding syncronising hyrdoelectric power stations.

I can see how a diesel fired station is controlled but I cant see how
you could control a hydro powered turbine.

I guess they generate ac and variable freq convert to dc and convert to ac.'


However, the converts would have to handle a huge amount of power and
perhaps not possible to build such a device.

Any ideas.

The web didn't want to play.

Cheers Justi

2011\05\08@031234 by Sean Breheny

face picon face
Hi Justin,

I googled "hydroelectric generator synchronization" and after trying a
few of the hits, I came upon this little gem of a paper:

http://andrewferguson.net/wp-content/uploads/2008/04/boulder-hydro-paper.pdf

At least in this one example of a relatively small (20MW)
hydroelectric power station, they synchronize the generators by
varying the water flow rate through the turbine which then speeds up
or slows-down the generator. A fly-ball governor performs this
adjustment continuously.

I did also see that there are SOME cases where they do convert to DC
and then back to AC but those seem to be only for very small hydro
plants.

The converters which you mention do exist but the only really high
power use I know of for these units is in long-distance DC power
transmission. The advantages of using DC for such long distances is
reduced losses (due to capacitive coupling and EM radiation) and
relieving the need to synchronize phase (which is difficult to do
between two ends of a very long transmission line with a varying
load). I believe that these converters are made using large stacks of
semiconductor devices in series, carefully driven and matched to
ensure that they share the voltage equally. They are very expensive as
you suggest.

Sean


On Sun, May 8, 2011 at 12:56 AM, Justin Richards
<spam_OUTjustin.richardsTakeThisOuTspamgmail.com> wrote:
{Quote hidden}

>

2011\05\08@080627 by Olin Lathrop

face picon face
Justin Richards wrote:
> I can see how a diesel fired station is controlled but I cant see how
> you could control a hydro powered turbine.

The water flow is controlled.

I once saw a generator being switched on line at a hydro power station in
northern Washington.  This was in the mid 1970s, so things are probably more
automated now.  They had a big dial on the wall, which must have been
showing the phase angle between the generator and the grid.  People were
manually fuzting with things trying to make the needle stay on straight up.
When it got close and steady enough for their judgement, someone flipped a
switch.  There was sortof a thud, and then that was it.

It seems to me that could have been done better and more reliably with servo
electronics, even in the 1970s.  Maybe there was some of that behind what
the people were controlling, but there was a surprising amount of manual
interaction.


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2011\05\08@081227 by Olin Lathrop

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Sean Breheny wrote:
> The advantages of using DC for such long distances is
> reduced losses (due to capacitive coupling and EM radiation) and
> relieving the need to synchronize phase (which is difficult to do
> between two ends of a very long transmission line with a varying
> load).

And no skin effect.  That means the conductors can be used more efficiently..

As you say, DC is usually reserved for long distance transmission.  The
power feed from Hydro Quebec is 100s of miles long, and is DC.  It ends at a
special power conversion station in Ayer, not far from my house.


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2011\05\08@094002 by Carl Denk

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Far from an expert in this area, but: I heard something recently, that once that switch was thrown to bring the generator online to the grid, the the electromagnetic forces took over. If the generator was trying to run too fast (governor set higher RPM), the load increased slowing the generator and bringing into phase, and if too slow, then the load was lessened and speed increased. There is probably a better explanation of the phenomena. The main generating station compares the clock to a standard time piece, and adjusts their speed to provide us with correct time within a second or so.

On 05/08/2011 08:07 AM, Olin Lathrop wrote:
{Quote hidden}

> (978) 742-9014.  Gold level PIC consultants since 2000

2011\05\08@100142 by Dave Tweed

face
flavicon
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Carl Denk wrote:
> Far from an expert in this area, but: I heard something recently, that once
> that switch was thrown to bring the generator online to the grid, the the
> electromagnetic forces took over. If the generator was trying to run too
> fast (governor set higher RPM), the load increased slowing the generator
> and bringing into phase, and if too slow, then the load was lessened and
> speed increased. There is probably a better explanation of the phenomena.

Yes, that's essentially correct. The entire grid and all of the synchronous
machines (generators and motors) attached to it function as though all those
shafts were physically linked together.

> The main generating station compares the clock to a standard time piece,
> and adjusts their speed to provide us with correct time within a second
> or so.

Well, there's no one "main" station, but the larger stations do adjust their
energy-input "throttles" periodically (on the order of minutes) in order to
keep the the grid's cycle count over the long term in agreement with UTC.
They don't worry too much about short-term variations, but a wall clock that
counts line cycles will be a couple of orders of magnitude more accurate over
the course of a year than a crystal-based one.

-- Dave Twee

2011\05\08@101613 by peter green

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face
Justin Richards wrote:
> The question has come up regarding syncronising hyrdoelectric power stations.
>
> I can see how a diesel fired station is controlled but I cant see how
> you could control a hydro powered turbine.
Are we talking conventional dam based hydro or "run of the river" hydro here?

To sync a generator to a grid you need way of varying the rotation speed.

In a conventional hydro plant with a dam and a turbine in a tunnel you would do this by adjusting the valve that feeds water down the tunnel to the turbine just as you would adjust the throttle on a fossil fuel powered engine.

In a "run of the river" plant things are trickier, if you wanted speed control you would probablly have to either have some kind of brake on the shaft or some way of feathering the blade. I suspect many of them aren't synced at all and use electronic approaches to get power to the grid but I dunno for sure.

There are various ways to tell if you are synchronised, a crude but simple method that works for small generators is to connect three lamps between the outputs of your generator and the grid. When all three lamps go off then you are syncronised. Bigger and/or better generators presumablly have something to measure the phase directly.

Once the switch is thrown the electromagnetics take over the synchronisation. The generators try to push the frequency up, the loads try to drag it down and a balance is reached. Someone (or something) in a central control room adjusts the total power generated and hence the overall frequency that the grid runs  at.

{Quote hidden}

>

2011\05\08@102448 by Justin Richards

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>
> http://andrewferguson.net/wp-content/uploads/2008/04/boulder-hydro-paper.pdf
>
Great article. Thanks.  My searches failed dismally

2011\05\08@102553 by Justin Richards

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> I once saw a generator being switched on line at a hydro power station in

I would like to see that

2011\05\08@103253 by Justin Richards

face picon face
>> The advantages of using DC for such long distances is
>> reduced losses (due to capacitive coupling and EM radiation) and
>> relieving the need to synchronize phase (which is difficult to do
>> between two ends of a very long transmission line with a varying
>> load).
I have pondered phase issues with long transmission lines particularly
when an area is fed by 2 different paths for redundancy, if they do
such a thing.

I always considered a varying signal to travel with less loss.  My
reasoning elludes me know

2011\05\08@104006 by Justin Richards

face picon face
> would do this by adjusting the valve that feeds water down the tunnel to

Intuitively, this would have issues dealling with sudden demand
changes.  Perhaps the majority of these system upsets are small
compared with the overall system capacity

2011\05\08@104734 by Sean Breheny

face picon face
I have often had the same problem - all it takes sometimes is one
person to think up just the right search terms and this list is great
for that :)

I looked at the article again and I do still think it is a good
article, but it also has a number of embarrassing mistakes. It has
many typographical errors and a few grammar errors. Worst of all,
though, in discussing 3-phase power it says "the net energy delivered
sums to zero" when I believe they meant to say "the net CURRENT
delivered sums to zero".

Sean


On Sun, May 8, 2011 at 10:24 AM, Justin Richards
<.....justin.richardsKILLspamspam@spam@gmail.com> wrote:
>>
>> andrewferguson.net/wp-content/uploads/2008/04/boulder-hydro-paper..pdf
>>
> Great article. Thanks.  My searches failed dismally.
>

2011\05\08@104817 by Sean Breheny

face picon face
oops, yes, skin effect would be significant, too.

On Sun, May 8, 2011 at 8:13 AM, Olin Lathrop <olin_piclistspamKILLspamembedinc.com> wrote:
> Sean Breheny wrote:
>> The advantages of using DC for such long distances is
>> reduced losses (due to capacitive coupling and EM radiation) and
>> relieving the need to synchronize phase (which is difficult to do
>> between two ends of a very long transmission line with a varying
>> load).
>
> And no skin effect.  That means the conductors can be used more efficiently.
>
> As you say, DC is usually reserved for long distance transmission.  The
> power feed from Hydro Quebec is 100s of miles long, and is DC.  It ends at a
> special power conversion station in Ayer, not far from my house.
>
>
> ********************************************************************
> Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
> (978) 742-9014.  Gold level PIC consultants since 2000.
>

2011\05\08@134147 by Olin Lathrop

face picon face
Justin Richards wrote:
>> I once saw a generator being switched on line at a hydro power
>> station in
>
> I would like to see that.

The one I saw was in or near the North Cascades National Park in Washington..
I just looked on a map, and it was probably either at the dam of Ross Lake
or Diablo Lake.  I got lucky that they were switching a generator on line
just when I happened to be there.  I don't know if they still run tours.

There are hydro plants all over the place.  Check around near you and maybe
some of them run tours.  Other plants I've been to include Grand Couley,
Bonneyville, and a coal/oil fired plant in Salem MA.

I'd like to see the Northfield Mt reservoir plant here in MA, but so far I
haven't been there when they were open for tours.  That one is really cool
in that they pump water a few 100 feet up from the river when there is
excess electricity, then have it drive the turbines during higher demand.


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Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
(978) 742-9014.  Gold level PIC consultants since 2000

2011\05\08@134926 by Olin Lathrop

face picon face
Justin Richards wrote:
>> would do this by adjusting the valve that feeds water down the
>> tunnel to
>
> Intuitively, this would have issues dealling with sudden demand
> changes.  Perhaps the majority of these system upsets are small
> compared with the overall system capacity.

Some types of hydro plants are actually reasonably fast adjusting to demand,
on the order of 10s of seconds.  Nukes take much longer than that, and
therefore generally provide the baseline power.

The current standard has the regional control authority sending requests for
power every 4 seconds.  The generally slow response of most electricity
generation is one reason having short term fast responding systems on the
grid makes sense.  These guys make large 100KWH flywheels with the
electronics to quickly store or retrieve power:
http://www.beaconpower.com/products/about-flywheels.asp

2011\05\08@145111 by John Gardner

picon face
Good book, but has gotten awfully expensive...

http://www.amazon.com/Electrical-Machines-Drives-Power-Systems/dp/0131776916/ref=sr_1_1?s=books&ie=UTF8&qid=1304880472&sr=1-1

Jac

2011\05\08@203825 by Bob Ammerman

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----- Original Message ----- From: "Justin Richards" <.....justin.richardsKILLspamspam.....gmail.com>
To: "Microcontroller discussion list - Public." <EraseMEpiclistspam_OUTspamTakeThisOuTmit.edu>
Sent: Sunday, May 08, 2011 10:25 AM
Subject: Re: [OT]:how are hydroelectric power stations synchronised


>> I once saw a generator being switched on line at a hydro power station in
>
> I would like to see that.

I used to develop control software for hydroelectric plants. The basic way a generator is synced in manually has been well described here: a device called a synchroscope displays the phase relationship between the grid and the generator. The 'scope looks something like a clock with a single hand. When the hand is at twelve o'clock the generator is in phase with the grid. The user's adjust the generator speed (for a hydro generator this is done by manipulating the 'wicket gates' that control the water through the turbine) until the frequency is nearly the same as the grid's frequency. This can be seen in the synchroscope because the hand will be rotating slowly around the dial. Then, as the hand crosses twelve the operator closes in the circuit breaker for the generator. Once closed in, the generator is forced to track the grid.

Automatic synchronizers work on the same principal, except that a computer (or in the past an electro-mechanical rube-goldberg system!) watches the phase relationship as it adjusts the wicket gates. When the frequency is close and the phase is going through 0 degrees it again closes in the breaker.

Closing in a generator that is out of phase can be very exciting.

A story...

In the 1980's we were developing a control system for the Niagara Falls Robert Moses power plant. The customer wanted us to implement a semi-automatic mode for synchronization: the operator would use the computer system to generate raise-and-lower pulses to the wicket gates, and, watching the synchroscope would then press a key on the keyboard to close in the generator breaker. We tried to explain to the customer why this was a bad idea (tm) but they wouldn't hear about it (more on that later). They insisted that we implement the mode.

During acceptance test the customer proceeded to test the semi-automatic sync mode, with the operator pressing the keyboard key as the synchroscope went past twelve o'clock. Unfortunately what the customer refused to understand was that there were inherent delays between pressing the keyboard key and the actual command to close the breaker being sent out (see analysis below). The net result is that a 160 MW generator was closed in approximately 30 degrees out of phase. It was like a large bomb went off! Luckily there was no permanent damage to the unit, although I understand the breaker needed some work.

Where did the delay come from? Well...

The microprocessor in the keyboard had to get around to scanning the key...
Then the keyboard had to send the keystroke over a serial link to the display processor, which...
Communicated via a multiplexed X.25 link with a communication processor, which...
Communicated over a bus interface with the main processor, which...
Examined the request and decided to close the breaker. So it...
Sent the breaker close command over a network to the front-end processor, which...
Communicated over a bus interface with a communication processor, which...
Communicated over a multiplexed communication link to the RTU, which...
Set a digital output to command the breaker to close.

The upshot: The customer insisted that we remove the semi-automatic sync capability from the software.

-- Bob Ammerman
RAm Systems

2011\05\08@210115 by Richard Prosser

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On 9 May 2011 12:38, Bob Ammerman <rvammermanspamspam_OUTroadrunner.com> wrote:
> ----- Original Message -----
> From: "Justin Richards" <@spam@justin.richardsKILLspamspamgmail.com>
> To: "Microcontroller discussion list - Public." <KILLspampiclistKILLspamspammit.edu>
> Sent: Sunday, May 08, 2011 10:25 AM
> Subject: Re: [OT]:how are hydroelectric power stations synchronised
>
>
>>> I once saw a generator being switched on line at a hydro power station in
>>
>> I would like to see that.
>
> I used to develop control software for hydroelectric plants. The basic way a
> generator is synced in manually has been well described here: a device
> called a synchroscope displays the phase relationship between the grid and
> the generator. The 'scope looks something like a clock with a single hand..

...snip.......
>
> -- Bob Ammerman
> RAm Systems
>
>
>


IIRC the earlier model of the "synchoscope" used two schyncronous
motors  - one driven from the grid and the other from the local plant.
The motors were coupled to a differential gear (like a cars diff - but
smaller) which driectly connected to the indicator. Frequency
difference was indicated by a moving indicator and phase difference
could be read directly as an offset from vertical provided the motors
were near - identical.

R

2011\05\08@212518 by Isaac Marino Bavaresco

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face
I have seen a simpler system: simply a (higher voltage) light bulb
across the same phase of the two generators.

When the generators are at different frequencies, the light flickers.
When the frequencies are closer, the flicker slows down.
When both are at the same frequency but different phases the light stays
steady.
When at the same frequency and phase, the light stays off.


Isaac


Em 8/5/2011 22:00, Richard Prosser escreveu:
> On 9 May 2011 12:38, Bob Ammerman <RemoveMErvammermanTakeThisOuTspamroadrunner.com> wrote:
>> {Original Message removed}

2011\05\08@215006 by Justin Richards

face picon face
> called a synchroscope displays the phase relationship between the grid and
> the generator. The 'scope looks something like a clock with a single hand..

Is this a mechanical device.  How does it use the two generator
sources to drive such a scope.

I guess a CRO on XY may be useful but what you describe does not
appear to be a CRO.


> The upshot: The customer insisted that we remove the semi-automatic sync
> capability from the software.
>

Nothing like a well executed demonstration to get the point across

2011\05\08@220715 by Bob Ammerman

flavicon
face
>> called a synchroscope displays the phase relationship between the grid
>> and
>> the generator. The 'scope looks something like a clock with a single
>> hand.
>
> Is this a mechanical device.  How does it use the two generator
> sources to drive such a scope.
>
> I guess a CRO on XY may be useful but what you describe does not
> appear to be a CRO.

The traditional synchroscope is electro-mechanical in nature. I am not sure how it is physically implemented, although I expect it might involve two synchros (or selsyns) or something like them coupled together. See http://en.wikipedia.org/wiki/Selsyn

See also: http://en.wikipedia.org/wiki/Synchroscope

-- Bob Ammerman

2011\05\08@220959 by Denny Esterline

picon face
Much good has been said, but all seem to have missed an important aspect of
the control equation - the generators have field coils.



-Denn

2011\05\09@000951 by David Challis

face picon face

> I have seen a simpler system: simply a (higher voltage) light bulb across
the
> same phase of the two generators.
>
> When the generators are at different frequencies, the light flickers.
> When the frequencies are closer, the flicker slows down.
> When both are at the same frequency but different phases the light stays
> steady.
> When at the same frequency and phase, the light stays off.
>
This mechanism is also used on the Boeing 727.  The flight engineer (the guy
sitting sideways in the cockpit) would switch in three ac generators onto a
common bus.  There was one generator per engine connect via a variable speed
drive unit.  The FE would adjust the speed of the drive until the flashing
yellow lights went out, and then close the circuit breaker on that generator
to add it to the AC bus.

Dave Challis

2011\05\09@071254 by Herbert Graf

picon face
On Sun, 2011-05-08 at 12:56 +0800, Justin Richards wrote:
> The question has come up regarding syncronising hyrdoelectric power stations.
>
> I can see how a diesel fired station is controlled but I cant see how
> you could control a hydro powered turbine.
>
> I guess they generate ac and variable freq convert to dc and convert to ac.'
>
>
> However, the converts would have to handle a huge amount of power and
> perhaps not possible to build such a device.
>
> Any ideas.

Pretty much the same as any generation source.

You bring everything up off the grid, synchronize to the grid, and then
"throw the switch" putting your generation on the grid.

The generator will then remain synchronized to the grid, acting as a
generator when you put more water through it, acting as a motor when you
don't put enough water through it.

Kinda simplistic description, but the reality is fundamentally just
that.

There is no conversion to DC and back or anything like that. Only cases
where that is true is either Solar (where the generation is DC) or some
(most?) wind generation.

TTYL

2011\05\09@072008 by Herbert Graf

picon face
On Sun, 2011-05-08 at 09:40 -0400, Carl Denk wrote:
> Far from an expert in this area, but: I heard something recently, that
> once that switch was thrown to bring the generator online to the grid,
> the the electromagnetic forces took over. If the generator was trying to
> run too fast (governor set higher RPM), the load increased slowing the
> generator and bringing into phase, and if too slow, then the load was
> lessened and speed increased. There is probably a better explanation of
> the phenomena. The main generating station compares the clock to a
> standard time piece, and adjusts their speed to provide us with correct
> time within a second or so.

That's correct.

In my 3rd (or 4th, can't remember) power electronics course we actually
did that. We had a setup where we had a motor turning a generator with a
light bulb between it and the grid. Our aim was to adjust the motor
speed so that the light bulb remained as close to "off" as possible
(constant mean we'd matched frequency, off meant we'd matched phase).
Once we were close we'd throw the switch and the generator would be on
the grid.

Some students didn't really understand how things worked, lab time was
ending and they still hadn't gotten their generator on the grid. In an
act of desperation, despite their lightbulb blinking quite quickly they
threw their switch.

A huge thud, and breakers blowing were the only things heard in the
room.

Very "real" way to learn about these things! :)

TTYL

2011\05\09@074842 by Olin Lathrop

face picon face
Denny Esterline wrote:
> Much good has been said, but all seem to have missed an important
> aspect of the control equation - the generators have field coils.

No, it wasn't missed since it wasn't relevant to the discussion.  The output
voltage is a function of the excitation field strength, but has no bearing
on the speed of a unloaded generator.


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(978) 742-9014.  Gold level PIC consultants since 2000

2011\05\09@123704 by zipwize

picon face
The stator has the ability to " rotate" the excitation field so that the rotor produces output in phase with the Mains. The stator does not rotate, just the magnetic field. There are many windings connected to many cabinets and there is a phase meter on the main control panel that must match with in a degree before the generator is put on line. The stator is really impressive to see with the amount of separate field windings stacked in a giant ring. The stator cooling is done from the outside diameter.
Cheers,
Fred
{Original Message removed}

2011\05\09@151942 by Denny Esterline

picon face
>
> Denny Esterline wrote:
> > Much good has been said, but all seem to have missed an important
> > aspect of the control equation - the generators have field coils.
>
> No, it wasn't missed since it wasn't relevant to the discussion.  The
> output
> voltage is a function of the excitation field strength, but has no bearing
> on the speed of a unloaded generator.
>
> Respectfully disagree.
There's two parts (at least) to this conversation - How they _initially_
synchronize an individual generator to the grid, and how they _maintain_ a
generator matched to the grid.

Initially, yes, an unloaded generators' frequency can only be controlled by
the prime mover, but once it's connected to the grid and there's
load available it becomes a bit more complex.

-Denn

2011\05\09@155902 by Carlos Marcano

picon face
2011/5/9 Olin Lathrop <spamBeGoneolin_piclistspamBeGonespamembedinc.com>

> No, it wasn't missed since it wasn't relevant to the discussion.  The
> output
> voltage is a function of the excitation field strength, but has no bearing
> on the speed of a unloaded generator.
>
>
Yes it does. Increasing RPM will raise the terminal voltage of the unloaded
generator. We used to do this (although I agree it is not recommended) with
very old Westinghouse 230MW hydrogenators that were electro-mechanically
controlled  and sometimes the excitation system (dynamic systems)  was
unable to raise the voltage to the desired 18KV so we just pumped up a
little the speed through the governor system and get a few hundred more
voltages, to the expense of raising a couple more RPMs.

These are very antique gens, which need a lot of "tweaking" to get them
going.

Regards,

Carlos

2011\05\09@170347 by Olin Lathrop

face picon face
Denny Esterline wrote:
>>> Much good has been said, but all seem to have missed an important
>>> aspect of the control equation - the generators have field coils.
>>
>> No, it wasn't missed since it wasn't relevant to the discussion.  The
>> output
>> voltage is a function of the excitation field strength, but has no
>> bearing on the speed of a unloaded generator.
>>
>> Respectfully disagree.

You need to be more careful about what you quote.  I didn't say that last
part "Respectfully disagree".


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Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
(978) 742-9014.  Gold level PIC consultants since 2000

2011\05\09@172037 by Olin Lathrop

face picon face
Carlos Marcano wrote:
>> No, it wasn't missed since it wasn't relevant to the discussion.  The
>> output
>> voltage is a function of the excitation field strength, but has no
>> bearing on the speed of a unloaded generator.
>
> Yes it does. Increasing RPM will raise the terminal voltage of the
> unloaded generator.

You are confusing cause and effect.  The output voltage is a function of the
speed and exitation current.  Voltage is roughly caused by speed times
exitation current.  However, for a unloaded generator this does not feed
back to different load on the shaft since the load is zero by definition of
"unloaded".

Generators aren't perfect, so there will be some friction losses, eddy
current losses, etc.  Some of these will be effected by the exitation field
strength, but not much.  If a generator is 90% efficient, then these effects
are only issues to the 10% inefficient part.


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Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
(978) 742-9014.  Gold level PIC consultants since 2000

2011\05\09@182918 by Denny Esterline

picon face
<snip>

> >> Respectfully disagree.
>
> You need to be more careful about what you quote.  I didn't say that last
> part "Respectfully disagree".
>
>
<snip>
Curious, when I look at my post in Gmail - it doesn't include that as part
of the quote. Looks like we've found another e-mail client bug.

-Denn

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