MadSci Network: Engineering

Re: Re: Re: Why does it take so long to restart power generators/electrical stations?

Date: Tue Aug 19 00:24:41 2003
Posted By: Donald Howard,
Area of science: Engineering
ID: 1061077336.Eg

A complicated question about a complicated subject probably best covered 
face to face, however, that is not an option here.  

First, an outage is a controlled blackout.  You are questioning the recent 
repeat of the 1965 "Northeast Blackout."  First, most plants do not 
have "Black Start" capability - they depend on grid power to start the 
fans, pumps, and controls needed to fire up the boilers, roll the 
turbines, and synchronize the generators to the grid.  Steam may or may 
not be available at the proper pressures for a restart, but that is only 
part of the problem with an areawide grid outage.

Each plant can only supply a portion of the load, and as you say, they 
should be able to supply a small "island" if it can be assured that a. the 
required transmission lines are intact, and b. the generator won't be 
overloaded the second it is synced to the local grid.  That takes a 
verification by Distribution Engineering that the total connected load for 
the circuits to be recovered is less than the capacity of the generator(s) 
to be reconnected.  Then it must be verified that ONLY those circuits are 
connected and NOT any others - sometimes that requires a visual inspection 
of the breakers at the local substation.  Somebody has to go out and 
look.  Usually, this happens in foul weather, so that isn't the easiest 
thing to do.

Since all of this is far from routine operation, even if the utility has 
procedures for performing the required actions, the rule is that the first 
time you do something it takes five times longer than if it is something 
you do every day.  Since the last time this happened was 38 years ago, I 
would assume that anyone involved in the recover from that blackout has 
retired, so this is all being done by a "green" crew who will proceed 

Plants and systems along the edge of the blackout area usually are the 
first to recover as they can connect to an operating system on the other 
side of that edge to borrow power to start those pumps and fans required 
for boiler/turbine restart.  Of course, that's once the necessary 
transmission lines have been verified as operable.

Most of the nuclear plants are capable of Black Start, but are restricted 
from doing so by a license requirement specifying the amount and type of 
off-site power they need to begin to startup.  Plus they suffer from 
a "paper interlock" that requires extensive forms and checklists to be 
completed and verified, and one of the obvious requirement of those forms 
is to identify the cause of the shutdown.  A fact that nobody knows as of 
this writing.

I have been involved in one plant blackout caused by a heavy, wet 
snowstorm.  That plant had 11 transmission lines connected to it's sub 
station, and they all came down as a result of icing.  In places those 
lines were covered with ice a foot in diameter.  

This particular plant was old enough to have black start capability, and 
plenty of steam.  The only person there who had ever participated in a 
black start was the plant superintendent.  He operated the auxiliary 
equipment necessary.  He had one main turbine almost up to speed to be 
able to carry "House Load," and to start the auxiliaries for the other 
boilers and turbines when the line crews finished repairing one 
transmission line and power was supplied from off-site.  The remainder of 
the restart was then routine, and the crisis was over.

From what I saw in satellite photos, there were "islands" of light visible 
within the blackout area a few hours after sunset, so some of the plants 
and systems were more easily restored than others.


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