[Lowfer] Power Outages

Mon, 18 Aug 2003 19:10:46 -0400

Thanks, Dennis! Great explanation.

FYI, Nuke plants work pretty much the same. The major differences are:

- it takes a lot longer to get the boiler back to operation once the reactor
scrams and the rods drop. Usually about two days.

- Nukes have two dark start generators assigned: One on-site (usually gas
fired) and one off-site. Both must be operational before a reactor can spin
the generators back up.

- For nuke plants, primary site power MUST come from a separate off-site
feed. Back feeding is not permitted. The remote source must be from a
different zone on the grid. I have seen plants run lines for 300 miles to
get site power.

Mike
wa1ptc

> -----Original Message-----
> From: [email protected]
> [mailto:[email protected]]On Behalf Of Denis Cote
> Sent: Monday, August 18, 2003 5:21 PM
> To: Lowfer@Mailman. Net (E-mail)
> Subject: RE: [Lowfer] Power Outages
>
>
> 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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