Comments about technological history, system fractures, and human resilience from James R. Chiles, the author of Inviting Disaster: Lessons from the Edge of Technology (HarperBusiness 2001; paperback 2002) and The God Machine: From Boomerangs to Black Hawks, the Story of the Helicopter (Random House, 2007, paperback 2008)

Saturday, February 5, 2011

Texas Sheds a Load: ERCOT and rolling outages

Watching with interest the slow trickle of information from trade magazines and the Electricity Reliability Council of Texas (ERCOT) about how 50-odd power plants in the Texas grid could have tripped in a short time, requiring load shedding of distribution sectors that cut off millions. Some zones lost power repeatedly, some just a single time for 45 minutes. Some zones never lost power.

The official story continues to evolve and emerge. A few operators like Luminant have identified plants that went offline. One of those was Oak Grove, a lignite-powered 1,600 MWe facility that won an award from POWER Magazine in 2010 for Plant of the Year.

Meanwhile, most of the 50-odd plants that tripped remain anonymous ... says ERCOT, they can't tell because that's proprietary information under "market rules." 

Market rules? Texas is one of those states that began deregulating its electricity market in the pre-Enron-fraud age of optimism. Post-Enron (centered in Houston, by the way), few regulated-market states continued down the path of full deregulation; the current trend is more of a hybrid. Some fully-deregulated states have been unpleasantly surprised by retail price hikes.

So in the last few days ERCOT-bashing has been underway, but in such a crisis, load shedding is the right thing to do. A federal report analyzing the August 2003 Northeast blackout determined that had FirstEnergy or the ISO quickly shed about 1,500 MW of power going to the Akron-Cleveland area, a full blackout probably wouldn't have happened. (FirstEnergy responded that a bigger factor was a lack of reactive power across the region, a phenomenon unique to alternating-current systems that can be analogized to the momentum of a moving body.) 

Load-shedding is disruptive and should have been avoidable, but it was a big storm and it's a lot better than losing a major portion of the grid, which can happen if the 60-hz frequency drops too low. In such situations big plants can take the better part of a day to come back up. 

Load shedding orders having gone out under a declared emergency, ERCOT did what it could to summon all available electrons to service: allowing some plants to run beyond their normal rating given air pollution control equipment; it drew a few hundred megawatts from Northern Mexico through the brand-new Sharyland direct-current intertie crossing the Rio Grande, and even requested black start generators to join the busbars. (Black start generators are relatively small and inefficient plants, normally used only to energize big power plants and get them going ... something like the little gasoline starter-motors that diesel-powered bulldozers used to employ.)

In 1985 I wrote an article about blackouts that noted DC interties can be critical in sharing power that prevents massive blackouts. They're "asynchronous," meaning that a disturbance in one grid doesn't spread to the other. 

Many theories have been echoing around the Net about possible causes: frozen water pipes, too little gas getting to gas-fired generators because of dastardly old state regulations that favored residential accounts, wind not providing enough power because some were idled due to ice on the blades, and unexpected demand that swamped ERCOT's day-ahead planning. 

Hmm. ERCOT and all such independent system operators say they are obsessed with weather reports, and this blizzard was well advertised. Here's an article from 2003 about ERCOT's control room and how they have the Weather Channel up at all times. 

Even more than what happened in ERCOT's control room, I'm  intrigued about why dozens of plants would go off line about the same time. Gas shortages don't go far in explaining it. 

Here's one theory I find plausible for some of the generator trips: the control systems. Specifically, water vapor freezing in unheated instrument-air lines and gas-pipeline valves. Water vapor can play havoc with instrument-air lines. See this article for a detailed explanation of how water that got into instrument-air lines initiated a chain of events leading to the Three Mile Island Unit 2 near-meltdown.

1 comment:

  1. Atmos Energy did say that gas fired generating plants have lower gas priority than commercial buildings in one press release. Yet, how many commercial businesses can run without commercial electric power?

    I do think building more DC interties is a good idea for electrical reliability. A HVDC Regional intertie might have made the Western Intertie overstress Blackouts of August 1996 less likely.

    Yet, the simple task of keeping tree limbs from touching powerlines could do wonders. Several large power failures (10 August 1996, 14 August 2003) have had this problem as one of the root causes (no pun intended).