[Lowfer] Power Outages

Wed, 20 Aug 2003 06:15:36 -0400

Denis

Interesting stuff. Thanks for taking the time to explain the startup and
shutdown. Sounds like the control room would be a great place to spend some time!

Jay

Denis Cote wrote:

> (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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