Re: Removing impedance protection from MOEPED #3

From: daestrom (daestrom_at_NO_SPAM_HEREtwcny.rr.com)
Date: 12/22/04 

Date: Wed, 22 Dec 2004 17:04:34 GMT

"Ignoramus29457" <ignoramus29457@NOSPAM.29457.invalid> wrote in message
news:cq9vi9$45k$0@pita.alt.net...
>I am confused about something. Even if a power plant requires external
> power to start (say, fuel pumps should be operating for some time
> before water heats up and boils), it would require a lot less power
> than it produces. Probably many many times less. If so, then a power
> plant can buy a generator of adequate size, say 1000 kW. It should
> cost a relatively minuscule amount compared to the cost of the power
> plant itself.
>
> This is completely analogous to having an electric starter on an
> engine. A small, cheap piece that can get stuff moving before the main
> power plant starts up in a self sustained mode.
>
> So, just what is the problem?Have them buy adequate generators and
> that's all.
>

Once a plant has started up, it certainly does produce more electricity than
it uses. A lot more. One plant I've worked at has a gross output of 880MW
electric. The 'hotel load' (the power needed to run the plant at full
power) is app. 30MW. So the net is 850MW.

But to start up, it needs about 15 - 20MW. And the main turbine is
producing zilch. Can you imagine how many diesel generator sets that would
take? A nice EMD V-16 can produce about 4MW. So, get about 5 or 6 of
those, connect them together with the correct switch-gear and controls and
have at it. But you will need this setup about once every 20 years, when a
major blackout such as 8/14/2003 occurs. That's a lot of hardware and
preventative maintenance for something you only need every 20 years. And 5
or 6 EMD V-16's with 4160V 4000kW output are not 'small, cheap pieces'.

So quite a lot of plants are not 'black startup' capable. The local grid
has to be 'up' to supply them with power to enable them to startup. Once
they *do* get on-line, it's a different story. But getting there is where
they need external power.

Take that nice diesel gen set you recently got. It's output is something
like 10kW right? And it just needs a nice 12V battery and electric starter
to get going. That's certainly affordable as opposed to a pull-rope. But
now imagine it scaled up by a factor of 100 000 so that you have a 1000MW
plant. In such a case even the 'cheap pieces' to start it would be very
expensive.

Some types of plants are much more easily made black start capable than
others. Hydro is perhaps the easiest. But even they need some
standby/emergency power for lubrication, gate-controls, cooling and such.
Modern gas turbines are probably also pretty easy to black-start. Steam
plants are some of the most demanding since they require a lot of pumping
power for the feed-water, and the boilers need quite a bit of auxilaries.

Then of course since most plants were built in the era of monopolistic
utilities with state regulation, you have to justify your plant's cost to
the regulators. The public service commission acknowledges that not *all*
the plants in a region need to be black start capable. They would not allow
such an 'extravagance' to be past on to the rate payers.

daestrom

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