Balancing the load - On a grand scale

[John Newman, Jr.]

The subject of load balancing has been discussed here numerous times and for most of us it usually involves keeping both legs of a 240 / 120 system within their rated capacity, or in other cases managing a 3 phase system.
Another consideration is the amount of 'droop' the system can handle when a large load is dropped onto the generator.
Imagine having to manage a system where, within a few minutes time, a 3GigaWatt (That's 3000 MegaWatts) load would be switched on and you have to keep the grid stable.
That is this guy's job:
http://www.wimp.com/britskettles/

[IanR]

That is relly impressive. Huh, no pressure at that job
The funny thing is, I would have thought, in this day and age, it would have been more automated.

[armandh]

mostly it is automated, such that the most expensive is dropped first and least expensive added first with due consideration to transmission loss and transmission capabilities.

a utility engineer from our street told me in the 1960s that the fellow running the board could save or loose his yearly salary in a few minutes.

back then it was all coal and hydro.

today it is that plus nuke for the big load and gas turbine for the spot needs

[armandh]

PS

dropped or added includes the output power raised or lowered

[Elden DuRand]

John:

Add to the pressure ..... It takes several minutes to get the largest turbines up to speed so the startup time must be considered.

I guess that they start the units they think they'll need ahead of time so they are ready to go online when needed. I also suppose they could have them online and idling at zero power output 'til needed, then they could either increase the voltage or the input to make them push kilowatts into the grid.

Interesting stuff.

Take care - Elden
http://www.oldengine.org/members/durand

[armandh]

I remember that with the two main steam turbine generators operating seperate busses and going to one in port required first paralleling then picking up the load on one as the other shed load. then tripping the lightly loaded gen off line. repete the proceedure shifting to shore power

[snowcountryfarmer]

Hmmm....I would say that a bit of drama has been added here. Certainly this is not a problem unique to Britain either.

Usually, about 5 o'clock in the morning, as chillers cycle on, lighting, etc. the power demand of large cities is staggering, in terms of block loading. This is a major problem in older cities, or older parts of cities. For example, in lower manhattan, in New York City, it is fairly typical to experience a voltage drop of 10% or more between 5 and 6 am.

The interesting thing to me, is that Britain actually has frequency deviation issues. Here in the US, the electrical grid is so large, that the frequency is VERY stiff. Voltage can fluctuate quite a bit based on the stiffness, or weakness of an area's lines, distance from transmission lines, etc. Put a fluke meter in any receptacle at any time in America, and you WILL measure 60hz, unless the power is going out about .5 second from when you are measuring...

[Andrew Mackey]

Here in the US of A, most of the control is automatic. This can lead to huge headaches for the power companies, if there is a problem. A few years ago, a Solar Flare created a power surge that blew out a substation. The domino effect knocked out the entire east coast and part of Canada, before manual control stopped it. We are told it won't happen again, BUT???
Andrew

[m_thompson]

A few years ago, a Solar Flare created a power surge that blew out a substation. The domino effect knocked out the entire east coast and part of Canada, before manual control stopped it.

Not the entire east coast. A very sharp operator in Rhode Island saw the cascade heading east and disconnected Rhode Island from the grid. We never even saw the lights flicker.

[snowcountryfarmer]

Well...actually most of the grid in the US is somewhat automated, but is completely overseen by live operators.

Basically, large transmission and distribution systems have complex mechanisms to trip automatically, for safety reasons (mostly equipment safety, not necessarily life safety), and to protect the integrity of the grid as a whole. Breaker reclosure is automated on a very limited basis for the same reasons. When reclosing and reenergizing a city block, for example, the inrush current can be staggering, and often large customers have to manually open their load breakers and reclose them after the line voltage returns in an organized and sequential manner, to avoid tripping their utility feeder breakers.

As far as steam and gas turbines go, their warm up times are not minutes but hours, and need to be carefully brought up to temperature to avoid problems with expansion and contraction of the very large casings and shafts, among other things. Like our generators at home though, these units also have governors and can be run at varying load levels (and varying fuel consumption levels) At any given time, there are hundreds of megawatts of generation capacity, steam and gas turbines running in spinning online idle, which means they are hot, connected to the grid and running under minimal load, but ready to kick the governors if the power is needed.

I doubt very much that any operators anywhere were able to isolate their area in the northeast blackout, these things move very quickly and are hard to anticipate. The area I live in didn't have any outage during the blackout, (northern NY) but we have lots of hydro plants in the area, not a lot of population/load and presumably the protective features of the grid in the area did their jobs properly. The problem arises when an area can't disconnect itself from the grid and maintain its load through local generation. For example, if your local utility has base load of 500 MW, and only 250MW of generation, it doesn't matter if they isolate themselves or not, they simply cannot support local load with local generation.

The real root cause of the northeast blackout, was that the large loads are basically centered in the large cities (new york, boston, etc) and the generating plants that feed these areas are ohio, pennsylvania, far northern NY, canada, etc. Decentralized local generation would have certainly helped out a lot.

Another interesting thing on the horizon is actually load regulation. Try looking up 'smart grid'. Up until this point, the generators and grid are adjusted to account for the load, which is completely variable. The new idea is to send signals over the power lines to shut off your water heater, or send your washing machine or dryer a signal to run (after you load it and put it in a sort of standby mode) in the middle of the night, when the load normally drops down considerably.

Interesting stuff.

[Gunny]

Nice movie clip but that ain't how it works.

Mostly automated.