[Lowfer] Power Outages

Tue, 19 Aug 2003 22:10:02 -0400

(I know I'm deviating from the Lowfer subject here, but this is good stuff!)

Jay,

Summed up briefly this is how we connect to the grid...

-Boiler steam pressure approaches 700 PSIG, we start pulling vacuum via the
condenser. At this time boiler fires are continuing to increase boiler load
up to max operating pressure; 1925 PSIG throttle. We typically light off the
boiler with No. 2 oil followed by No. 6 oil for max BTU's. We then phase in
pulverized coal when approaching maximum generator load then switch out the
oil. Of course, electrostatic precipitators are in operation to keep
surrounding neighbors happy.

-While the unit is on turning gear, the turbine lead valve is opened, main
steam stop valve is bypassed and we begin to roll the turbine via Full-Arc
admission. That is all governor valves of the turbine are fully opened
allowing steam to enter the turbine. Once we are on line and control load,
we switch to Partial-Arc admission. This method controls the governor valves
sequentially.

-Once we begin rolling the turbine, the DCS control system brings up turbine
speed up to 3600 RPM. This is performed by following a speed profile to
reduce turbine vibrations as it passes through critical speed points.
Bringing speed up too fast will have potential for initiating a vibration
trip or turbine rub due to thermal expansion differences. When normal
operating speed has been reached, the turbine/generator is held and allowed
to temperature soak.

-The generator is then synched to the power grid to match the grid frequency
via a synchroscope. Once matched, the main generator OCB is closed and we
are on the power grid. We notify ISO New England and start increasing load.

Denis

-----Original Message-----
From:	[email protected] [mailto:[email protected]] On
Behalf Of Jay Rusgrove
Sent:	Monday, August 18, 2003 6:04 PM
To:	[email protected]
Subject:	Re: [Lowfer] Power Outages

Denis

Very interesting. And how do you bring it back on line and "sync up"?

Any ideas on what really happened last week?

Jay Rusgrove, W1VD

Denis Cote wrote:

> Hi Pete,
>
> I'm employed at a coal fired power plant in Somerset, MA. Our facility has
> (1) 100 MW steam powered generator and (1) 22.5 MW jet driven unit for
black
> start capability.
>
> To help answer some of your questions without going into a lot of
detail...
>
> Generators are taken off line or "tripped" by the opening of the main
> breaker commonly referred to an OCB (Oil Circuit Breaker) connecting the
> generator to the power grid. All in all, think of it as a large knife
switch
> that is thrown. This typically happens with a sudden or emergency shut
down
> followed by the closing of the main steam stop valve feeding steam to the
> turbine from the boiler. Overall, plants like to discourage this type of
> event because it is a sudden and abrupt event, but in the case with the
> cascading effect of the blackout most plants were probably caught in this.
> Plants also trip due to phase changes detected on the grid itself, such as
> the line phase or load swings. The plant I work for is designed to trip if
> the line phase goes above or below a couple of Hz.
>
> A controlled trip is usually performed by slowly phasing the generator off
> the grid (hence, reducing MW output while maintaining 60 Hz line
frequency),
> followed by reducing fuel to the boiler producing steam. Once load has
been
> reduced down to a couple of megawatts, the main OCB is opened and the unit
> is tripped by initiating the MFT known as the Master Fuel Trip. This
> shutdown ceases all fuel to the boiler, putting the fire out, and closing
> the main steam stop valve to the turbine. Once this occurs, the
> generator/turbine is allowed to freewheel from 3600 RPM down to a few RPM
> and the unit is placed on turning gear. Turning gear is performed to allow
> the unit to rotate and cool down uniformly due to high turbine
temperatures
> near 1000 degrees. Last to mention and prior to the unit trip is that
> auxiliary systems such as pumps, control systems, computers and lighting
> still require power to function. Breakers are switched over so that the
> power grid can back feed the plant and no interruption of power occurs
> during shutdown.
>
> Typically, power generators are 3-phase AC and output 14-15KV. The
generator
> field or stationary windings are excited with an external DC voltage
supply
> known as an exciter. This voltage of approximately 375 volts is fed
through
> commutator or slip rings via carbon brushes mounted on the generator
shaft.
> This is the typical case with our plant generator, Unit 6, which is a 1959
> General Electric 120 MW hydrogen cooled generator. Following the main
> generator output leads, 14KV is fed parallel to two (2) separate
> transformers. One being a 14KV-115KV step up transformer which feeds
through
> the main OCB followed onto the power grid for transmission. Note that
larger
> power plants step up power to 345KV and higher dependent upon transmission
> requirements. The second transformer is a step down transformer that
reduces
> the generator output voltage to 2300 volts needed for plant station
service.
> This power supplies all pumps, fans, auxiliary systems and lighting
> necessary for the plant to operate.
>
> FYI, if we did not have any phone or radio comm in our control room, we
> would have never known of the blackout. No bumps or brown outs were
> encountered on our end.
>
> Denis - W1WV
> Swansea, MA
>
> -----Original Message-----
> From:   [email protected] [mailto:[email protected]]
On
> Behalf Of Peter Barick
> Sent:   Monday, August 18, 2003 3:14 PM
> To:     [email protected]
> Subject:        Re: [Lowfer] Power Outages
>
> >>> [email protected] 08/15/03 09:24PM >>>
> >> Okay it's not you. What about Mitch?
>
> >Bit of an update - Lost power here ( in my neighborhood ) for 11
> hours.
>
> >MP update - back on the air   137.780  today ( Friday 9PM EDT ).
> >Mitch
> ----------------------------------
> Heh-heh, good that's important. Yah, thought about Mitch Thurs., the
> last day I was Web connected, he being right on top of the "Lake Erie
> Grid." That's the first I heard of that artifact too.
>
> Being near the Chicagoland area and nearer to one of the power nukes I
> am aware of the power distribution fields that emanate west and head
> east into a network, but didn't know where that extended: to Ohio? PA?
> NY? Didn't know and, like most, didn't care before 8-14. Now,
> post-Thursday, it's the talk: The Power Grid! Ipso facto, guess the IL
> one extents to Indiana and foregoes that Erie "round-about." Nice
> concept when it works ... hmm. I have a few questions from the past few
> days of news accounts and some reporting gaps. Maybe some on the list
> are power industry savvy and could answer.
>
> 1) How is a power generator taken off (or put back on) the power grid?
> I think some envision a large knife-switch being operated, which I
> reject, but somewhere contacts have to be broken, no? (Ha, maybe this is
> where the concept of electric welding began.)
>
> 2) Do all plants generate 3-phase? What are they timed to?
>
> 3) What controls the period, currently 60cps? Is it the armature speed
> at some integral of 60?
>
> 4) Can a generating plant have it's load removed (say by some event
> outside the plant, unplanned) without consequence to the generator, ie,
> one moment pushing mega electrons, the next not?
>
> 5) Knowing of this recent "cascading effect" of the generators going
> down, as on Thursday, is that a very robust system or an engineering
> crap shoot? If the latter, how'd they get away with dumping it on the
> public and their national security?
>
> Enuf, any care to shed some "light" on this socio-engineering issue?
>
> Peter
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