Texas Rolling Brownouts 4

[electricpete]

What's the scoop with the rolling brownouts statewide on 2/2/11?

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[electricpete]

http://www.chron.com/disp/story.mpl/business/energy/7427513.html

While 8,000 megawatts was the peak outage, over the course of the day 82 power plants with a combined generating capacity of 11,000 megawatts went off line.

Forty percent of the plants that went down were powered by coal, 59 percent by natural gas and 1 percent by wind

....Many shutdowns were due to the failure of equipment monitoring different aspects of the plants, such as temperatures, pressures and water levels, as well as the failure of some control systems.

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[bacon4life]

I am still interested to know how the “ wind power units ... produced at levels they were expected to" compared to nameplate ratings of the turbines. Since not much wind is expected after a cold front settles in, it might be a matter of living up to some low expectations.

 

[rmw]

The cold front was still marching southward steadily when the blackouts occurred. Strong winds behind a cold front are a typical weather condition in this area as I think they are in most. This was a fairly strong front. I don't have any doubts about the reports of wind performance and I am not a very big fan of wind otherwise.

rmw

 

[tlrols]

Quote <You cannot "ship" electricity further than 900 miles without losing over 70% to heat losses in the power lines>


Wow...when did THAT happen? I had NO idea that Texas losses are so much bigger than anywhere else. I find it interesting that Portland General and Puget Sound Energy have had great success with scheduling energy from Colstrip, MT to their respective load centers...last I looked Colstrip was around 900 miles away!

Now, to be fair, I will agree that a 500 kV line with no intermediate stations (with compensation) isn't going to work so well after 300 or so miles...However, a claim of 70% losses (presumably on a transmission line) is a laughable statement. A typical 500 kV line at 700 miles would have a resistance of around 22 ohms--hardly a scenario where 70% losses would occur.

Just for fun I took a look at a WECC model, and found that no 500 kV line had losses greater than 3%.

 

[bacon4life]

Here are links to some wind speed data for February 2, 2011. Looks like the wind stayed blowing like rmw pointed out.

Dallas

http://www.wunderground.com/history/airport/KDFW/2011/2/2/DailyHistory.html

Odessa

http://www.wunderground.com/history...tml?req_city=NA&req_state=NA&req_statename=NA

Lubbock

http://www.wunderground.com/history...tml?req_city=NA&req_state=NA&req_statename=NA

San Antonio

http://www.wunderground.com/history...tml?req_city=NA&req_state=NA&req_statename=NA

 

[rmw]

I was present for the event and a victim too, I might add.

tlrols,

Could this be a semantics problem? RaCook goes on to comment about power being pushed (exchanged) rather than transmitted.

Now, in the interest of full disclosure, I am an ME. We just make the stuff - the power that is - then the EE's transmit and distribute it after performing some magic on it out in the switch yard.

But the way it was explained to me years ago is that when power was sold by a gulf coast utility to say, New York for example, that the power wasn't sent from the gulf coast to New York, it was just sent to the next utility north which then sent an equal amount off of their system to the next utility north until some utility delivered an equal amount of power to New York.

Was that over simplified, or did I miss something. And if it is an adequate description, was the power generated at Colstrip actually transmitted all the way to the west coast or just put on the grid there to be exchanged off the grid in Oregon?

I will still readily admit that about all I know about electricity is that it can kill you. But I am still teachable. So go for it if needed.

rmw

 

[electricpete]

Texas is an independent grid and not synchronized to the other grids. The only power interchange from Texas to East US, to West US and to Mexico is via DC tie lines. If you tried to put in just one or two long AC lines between Texas and East or West, it could cause stability problems during transients... the stability problems are related to the to the real power limit of the line: real power transmitted thru an inductance is approx P = |V^2|*sin(delta) / XL. When delta hits 90, you can see it's sort of an unstable situation since the line starts losing capacity...causing rapid excursions similar to out of synchronization condition. You'd need a whole lot of tie lines in parallel for stability.

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[electricpete]

As others have pointed out, the distance is not insurmountable...many other grids span much larger areas, but the system has evolved and grown without those rich interconnections, so establishing them now would require a lot of parallel lines.

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[rmw]

Pete,

What question are you answering?

There are small parts of Texas connected to grids other than ERCOT, so a power plant in Beaumont for example could "ship" power to New York City.

The 3 or so DC connections are fairly inconsequential with respect to the size of ERCOT and on the day in question, the grids that the DC connections are connected to were having their own issues and doubtful that they were a reliable resource for some stand-by power, but that is just a guess, not based on any facts.

I did wonder what the Tenaska units in Rusk County and Gateway were doing that day in that they have the ability to connect on an either/or basis to SWPP or ERCOT. Either grid at the time was more than likely having the same struggles.

The grids you mention are larger, but they have units spread all over them. Some units are sited specifically with respect to the grid's needs for real or reactive power as might be the case. Others are sited for reasons of fuel, water access, etc.

rmw

 

[electricpete]

What question are you answering?

racooke made some statements: "You cannot ship electricity further than 900 miles without losing over 70% to heat losses in the power lines". I took the statement in context of explaining why Texas is isolated... which is really the question/aspect I was addressing.

trols took exception with that exact same comment.

You responded to trols asking whether it was just semantics. Perhaps you were addressing a different aspect (beats me), but when you stated "Was that over simplified, or did I miss something", I thought something very important was missing with respect to the reasons the ERCOT grid is separate... hence my response.

I apologize if I misunderstood your comment or told you something you already knew.

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[tlrols]

Electricity CAN be transmitted over great distances using alternating current. It is simply a matter of voltage and series/shunt compensation. The assertion that the losses are 70% for a 900 mile long circuit is simply WRONG!!! However, would you build and operate a 900 mile long AC line with no intermediate stations--no. This is what you do with HVDC lines. AC lines should be looped into stations for compensation purposes at a minimum.

Texas, or more correctly speaking ERCOT, is not intercoonected to the rest of the United States (at least via AC links) for one simple reason...politics. FERC has NO jurisdiction over the commerical electrical activities within the ERCOT footprint since ERCOT does not cross state boundaries. In other words, the commerce clause of the US Consitution is not invoked, therefore, ERCOT (i.e. the State of Texas) defines the laws for doing commerical wholesale electrical business in Texas. Call it a Texas thing.

Racooke's assertion is not correct. You can operate an electrical system (note the word system) with the distance between any two points being several hundred miles. In general, the very rough rule of thumb for transmission distance (without intermediate stations) is 1 kV per mile. So, if you want to transmit power 500 kV, you would probably start looking at a voltage of at least 500 kV.

In the WECC northern Mexico is electrically connected to northern British Columbia as well as eastern Montana. Those distances are huge, approaching 1500 miles from Mexico into northern BC. This system works just fine by the way, everyday...and it is much, much larger than Texas!

 

[electricpete]

I agree the distance is not a huge issue. I understand that political factors have influenced the evolution of the current system.

I am also under the impression that providing an AC tie to the current system is not simple because of stability issues (you can't interconnect two big systems using only one or two long lines). To make an ac interconnection work requires several parallel lines like 5 or 6 or more as I heard once (I can't find any reference).

To my knowledge that's why all the interconnections that have been added are DC (east, west and Mexico), and the new interconnection is also planned as DC:

http://en.wikipedia.org/wiki/Tres_Amigas_SuperStation

Am I way off base on this?

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[rmw]

Just because Northern Mexico is synchronously connected to Manitoba, Canada does that mean that power is transmitted from Northern Mexico to Manitoba, CA?

I'm not much up on WECC. Beaumont, TX (the part of the Entergy system not in ERCOT) is electrically and synchronously connected to points way north of anything I know to mention in Eastern Canada, but I can't picture that they "ship" power that far even though I know that they sell power that far. I have been in plants in the Entergy system when they took on the contracts to supply the power. I can picture them putting power on Entergy's system (SWPP) and Entergy putting power on TVA at its NE corner on the way to points north and several grids later.

Isn't that what the term "wheeling" power means?

I'm not being argumentative, just asking.

rmw

 

[electricpete]

I agree, for the most part, power flows where it wants within the grid. We can identify precisely the power flow along a given line. But in a grid, who's to say which MW is going to which load. It is subjective, although there is plenty of bookkeeping that goes with it. It is certainly possible with proper bookkeeping to put power in at one location and take power out at another location and treat it as a transaction. Such transaction may or may not have a cost to the grid and may or may not be passed on the the people involved in the transaction.

Setting the bookkeeping aside, it is in my understanding an unstable situation to interconnect two large systems with one or two weak (long) ac transmission lines because transients can force large power flow through those lines which can exceed their stability limits. Most grids tend not to have that feature (2 large blocks connected by a weak connection of few lines), instead they are much more interconnected which generally improves stability.

Sorry if I have brushed aside your issue. Two different issues. Both interesting.

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[bacon4life]

Here is the FERC/NERC report on the outages.

http://www.ferc.gov/legal/staff-reports/08-16-11-report.pdf