Where were the blackouts and why?


Whether you got hit by a rolling blackout when the temperature hit the 20s this week may depend on how much electricity your neighborhood uses when it’s in the 90s.

CenterPoint Energy, which distributes power in the Houston area, uses a neighborhood’s curve — what its power usage looks like on a line graph representing a year — as a starting point in creating a list of which power circuits are subject to rolling blackouts. If your usage doesn’t change much between the winter and the summer, for example, it would be a flat curve.

The process is complicated but here, in general, is how it works:

CenterPoint’s Houston-area customers are divided into four groups for purposes of dealing with statewide power emergencies like the one Wednesday, during which hundreds of thousands of customers endured repeated rolling blackouts lasting up to 45 minutes.

In one group are customers considered critical to public safety — including hospitals, waste-water treatment facilities, the downtown business district where Houston fire and police headquarters are, and the skyscrapers of the Galleria. These are exempted from any voluntary power outages. On the map below those are the gray areas.

In another group are customers served directly by high-voltage transmission lines, such as the large industrial customers along the Houston Ship Channel. They’re off the hook because suddenly cutting power to a chemical plant or refinery can create other serious problems, such as hazardous chemical releases. On the map below those are the yellow areas.

What remains are the hundreds of thousands of mainly residential and small business customers served by above-ground power lines. These are the ones that are called upon to help avoid major, system-wide failures, and they fall into two categories.

CenterPoint engineers first identify one group of circuits — power lines serving 1,000 to 3,000 customers each — that can be turned off immediately in case of a major power plant accident, said company spokesman Floyd LeBlanc. This might be the sudden loss of the huge 3,600 megawatt W.A. Parish power plant in Fort Bend County. On the map below those are the blue areas.

Engineers want the circuits on the blue list to have “flat” usage curves so they can know with some certainty the amount of power that will be cut out in such an emergency, regardless of the time of year, LeBlanc said.

“If you lost a big unit, you could have a sudden spike or drop of voltage or frequency on the system,” LeBlanc said. That could seriously damage equipment for both the customer and the utility.

In the second category are the circuits that were subject to the rolling blackouts on Wednesday, in red on the map.

Red circuit customers experienced multiple outages on Wednesday as CenterPoint rotated blackouts through those circuits.

CenterPoint tries to spread the red and the blue lists throughout its service area to prevent imbalances in the flow of power, LeBlanc said. Engineers also must make sure the rolling outages don’t cut all the power from individual substations, since shutting a substation down can cause equipment problems.

LeBlanc said the red and the blue groups don’t overlap, because catastrophic failure of a major power plant could occur during rolling blackouts, and the system has to be able to handle both simultaneously.
CenterPoint reviews the circuit lists every year, and they’re subject to change as more customers are added to the network and the distribution of power demand changes.

Does CenterPoint get pressure from politicians or wealthy Houstonians to tweak outage lists in favor of certain homes or businesses?

“We get a lot of feedback from customers, a lot of suggestions, after an outage,”LeBlanc said. “But we don’t get a lot of calls asking to be put on one list or another, because most people don’t know we have these lists, or understand how our business works.”

Rolling blackouts like the ones this week are rare.

The last one was in April 2006 when unseasonably warm weather swept the state at a time when 14,000 megawatts of power plant capacity was down for planned maintenance.

And LeBlanc said no major plant failure, of the type that would cut off blue circuits, has occurred in the nearly 30 years that he has been with the company.

CNP_RollingBlackOuts_Feb2_2011 Final

Tom Fowler

18 Responses

  1. Mike cur says:

    You can cite all the technical reasonS why, and nutters like this pdh42 can holler environmental wackos (oh the irony !) from the highest roof tOp in HIS sanitorium, but it still boils down to overdevelopment to an inffratructure that cannot handle it, and overpopulation by a greedy goota have more society.
    When tha right wing religeous nutters and Hollywood tenties both agree on the glorification of rediculously large families( yeah eight is enuf ) we got problems. They call it strange bedfellows. AND THAT’S NEVER A GOOD THING.

  2. dbtexas says:

    Wondered how long before the blame would be place on President Obama. pdh42 (as usual) did not disappoint. Then, there is Bob. Conspiracy theories abound. I am certain that President Obama stopped his concerns with the world and decided to irk a few Texans by ordering rolling blackouts. ERCOT is a high priority of his, I’m certain. Otherwise, Mr. Fowler, thanks for the good explanation. Appreciate the information – and the laughs provided by the the conspiracy mongers.

  3. Rice says:

    pdh42: Please cite some semblance of proof that Obama, Washington D.C., EPA, or ANY federal institution for that matter has jurisdiction over ERCOT. What do you think of Rick Perry? Perhaps he could have done a better job with running the uniquely state-owned and operated institution that is ERCOT?

    bob: A link to a google search with some random words thrown together of course will return search results. But does it constitute as supporting evidence of the implicit comment you posted? Please don’t waste our time. Mr. Fowler’s articles are insightful and this forum is important for those of us that actually care to solve problems.

    Below I’ll link to a few good reads that I’d point out to those interested in realistic dialogue, as we in the industry prepare for another big winter storm in just a few days. Of note is that electric grids generally come under more strain in the winter than in the summer. It’s a lot easier to forecast 4 months of 110 degree heat index than one week of sub-freezing temperatures with gusty winds and gas well freeze-offs in the midst of an otherwise normal, moderate winter in Texas.



  4. Breeze says:

    How come companies like Texas New Mexico didnt have to participate in the rolling blackouts? Or is your map just showing Centerpointe data?

  5. Jcrocker says:

    Wow, those of us that reside out here south of Magnolia off Nichols Sawmill Rd & Butera Rd must be horrible in the summer then as our power went out at 0630 and did not return till 1600 hrs.

  6. Kittyg says:

    Again….as usual…it is the ordinary little taxpayer who is asked to pay the piper! Big Industry…corprorations…etc. win again! What is the benefit of being a middle-class legal citizen in this country? Well, gee you get to fund all the rest of the country….including the illegals and you get no support and no assistance whatever! Time for a revolution!

  7. pdh42 says:

    If anyone wants to know why we are having rolling blackouts you might want to look at the EPA and Nobama…. Between them they are killing the energy sector whether you are talking about oil drilling, refining, coal mining or electrical producers…. They are doing everything that they can to decrease the amount of energy that we are using so that the price goes up radically so that “green” energy can compete…. With out that “gren” energy can NEVER compete against hydrocarbons…. If you ever listened to Nobama during the 2008 campaign you would have heard him say that gas prices NEEDED to go up to force people to conserve and electricity needed to triple or quadruple to again force people to conserve and to make it where “green” energy could compete…. This is what Nobama and his henchmen have wanted since the beginning….

  8. Contrary Dave says:

    I worked in chemical plants up north for a number of years. Always amazing that after going through some days when it never went above zero the prior year, first freeze of the next winter there were always problems. Steam traps malfunctioning, air line freezeups and the like. Just a matter of luck whether any of these caused real problems. And the first cold weather for a new plant always caused problems no matter how well designed or how many people scrambled around looking for them.

    Been back in Houston for 25 years now. Can’t recall any rolling winter blackouts. Maybe I’ve forgotten. At any rate, I asked myself what I would be willing o pay extra to avoid ever having them again. The answer was zero. Ask me what I would pay extra to be sure there was never a one to two week outage in my neighborhood in the summer, very different answer.

    So I had the 3d blackout in 5 hours start just as I was putting my leftover chicken noodle soup in the microwave. Oh, woe is me, life is terrible (sarcasm intended).

  9. RunningBear says:

    Nonsense, this is about the “boys” playing with their new toy, the smart grid! No regulations, no controls, Ye-Haw ridem’ Cowboy!! Wait till we have a real problem and they turn the lights out, then the govt. folks will be askin’ why the electric power boys didn’t know what they were doing.

  10. Tex says:

    I would be much more concerned with all the substandard housing than a rolling blackout.

    You would not be discussing rolling blackouts if we had qualified builders and a system where building inspectors were doing their jobs rather than being in the pockets of the builders and the developers.

    Takes more than two by fours and stuccko to build a house these days.

  11. jukester says:

    I am much more interested in how the Houston area rolling blackouts, compared to those which were applied ELSEWHERE in the State of Texas. e.g. was there equity in these applied blackouts, or did Houston recieve a disproportionate degree of reductions? I am wondering if the Super Bowl created a ‘priority’ for Dallas area as example, which Houston had to sacrifice to keep them ‘up and running’ in the media spotlight?

    • Tom Fowler says:

      I believe the request for power cuts were proportional to the amount of power demand a certain area has on the overall grid. Houston is roughly one-quarter CenterPoint was asked to curtail about 1,050 megawatts out of the 4,000 megawatts. North Texas (Dallas/Ft. Worth) also had to curtail but I couldn’t quickly find an article that mentioned it. San Antonio and Austin’s shares were much smaller. I think the Arlington Stadium complex did stay online but my bet is it had more to do wiht the fact that it’s probably served by high voltage transmission lines (not the lower voltage lines you see behind your house) that aren’t usually included in rolling blackout plans. Since these plans are pre-determined, I could see them leaving a stadium out of rolling blackout plans since it could be pretty dangerous to leave a building full of 60,000 people suddenly without power.

  12. Bill Duff says:


    The biggest ‘blackout’ was poor regulatory and market rules for cold weather conditions.

    The Natural Gas companies curtailed service to electrical generation plants under the contractual provisions for low price interruptable service.

    The Oncor/ERCOT curtailed electrical power to Natural Gas companies under the contractual provisions for low price interruptable service.

    They ‘killed each other’.

    Thus Texas and Texans were suddenly short on Natural Gas AND Electrical Power; though there is an abundance of both in the Lone Star State.


  13. Diane Baker says:

    I’m confused. My power rolled off 4 times and I am trying to understand why. So, the article states that areas with a flat curve (blue) were not rolled. Does this mean the red areas (which were rolled) have a curve that is NOT flat? After reading the article, I’m still not clear.

    • Tom Fowler says:

      It means the red areas are prob. not as flat. The blue areas likely aren’t completely flat, and some of the individual users could actually have extreme curves. It’s really the curve of the entire circuit you’re a part of and if it’s more even/flat. Sorry it wasn’t more clear. It’s hard to simplify this stuff down to made it concise and accurate. I think engineers would still have plenty to quibble about with the descriptions, and rightly so.

  14. Energy Moron says:

    Thanks Neighbor.

    Confirms we are a blue area.

    Is this like being a blue state?