April 17, 2006 News Media Release

Austin Required to Implement Rolling Blackouts

The Electric Reliability Council of Texas (ERCOT) – which manages the statewide electric grid – ordered rotating blackouts Monday afternoon, April 17, 2006 across Texas. Cities across the state were each assigned a portion of 1,000 megawatts (MW) that needed to be turned off or “shed” to keep the statewide electric grid in balance.  

The short supply situation was created by a combination of factors: Record temperatures that caused record electric demand for April and  14,000 MW of power plants off line undergoing annual maintenance and repair work. March and April are two of the months when this work is typically scheduled because electric demand is usually lowest during fall and spring months due to mild temperatures. In addition,  five generating units in the state tripped off line shortly after 4:00 pm, creating a shortfall in generation that required immediate load shedding statewide to prevent a total blackout of the statewide electric grid. If the statewide electric grid shuts down, it would take 3-5 days to get the system back up.

ERCOT Process
When a generation shortage appears possible statewide, ERCOT begins a four-step process.

Step 1:  Ask utilities across the state to start-up additional generating units, if available. If, after that, it appears the shortage might continue or grow worse, ERCOT initiates Step 2. At Step 2, large industries that have agreed to shut down when power supplies are low - are ordered to shut down.

Step 1 was implemented by ERCOT at 3:00 p.m. Step 2 was implemented at 4:00 p.m. After implementing Step 2, ERCOT expected the state to have sufficient power through the remainder of the afternoon. 

However, at about 4:05 p.m., five power plants in Texas -- two in north Texas, two in central Texas, and one in West Texas - tripped off line within minutes of one another. Total capacity of these plants: 1,685 MW. This sudden loss of power put an immediate and dramatic strain on the statewide electric grid.

ERCOT Orders Blackouts
After the five power plants tripped, ERCOT ordered rotating blackouts statewide sufficient to “shed” 1,000 megawatts (MW) of demand throughout the state. The order to shed load went out at about 4:13 p.m. Load shedding is actually Step 4 in the emergency process. Because of the unexpected loss of five power plants all at once, ERCOT had to skip Step 3.

Step 3 is for public notification. During Step 3, the public is informed through the media of the potential statewide shortage of power. An appeal is issued asking all citizens and businesses to reduce their demand for electricity to the extent possible. At Step 3, Austin Energy would activate Incident Command - initiating a process that would include email or telephone notification of Key Account customers by Austin Energy Key Account Reps who are on call 24/7.
 
ERCOT Load Projections
ERCOT had projected a peak load of 49,018 MW for April 17th, with 53,920 MW of available generation. At 5:00 p.m. the statewide load peaked at about 51,714 MW, and that was after shedding 1,000 MW of load statewide. Why the underestimate? No historic data for 100- to 101-degree April days.

How “Load Shedding” is assigned
Each utility, or Transmission and Distribution Service Provider (TDSP), served by the ERCOT electric grid was required to “shed” a portion of the 1,000 MW requirement. Shares were based on each entity’s percentage share of the statewide load. Austin represents 4% of the statewide load, so Austin was required to “shed” about 40MW of the 1,000 MW requirement. Austin was not alone.

The ERCOT grid serves 85% of Texas. There are 17 TDSPs (of which Austin is one) served by the grid. Each had a responsibility for a portion of the required load shedding. The 17 include Texas Utilities (Dallas), CenterPoint Energy (Houston), City Public Service (San Antonio), Austin Energy (Austin), American Electric Power (Corpus Christi) and the Lower Colorado River Authority, as well as utilities serving Bryan, College Station, Denton and Garland, to name a few.

Austin Energy Process
Austin Energy began rotating blackouts at 4:15 p.m. The Austin Energy electric system consists of about 250 circuits. Circuits that power emergency and community services such as hospitals and other facilities critical to public safety and the downtown business district are not candidates for rotating blackouts.

The remaining circuits are organized in random fashion. The goal is to spread rotating blackouts fairly across the community, with no one area of town overly affected at any one time. The process begins by disconnecting circuits until the required 40 MWs has been achieved (about 10-12 circuits). That group of circuits stays disconnected for about 10 minutes. Then, another set of 10-12 circuits are disconnected and the first group of circuits are reconnected. Each group of circuits served approximately 20,000 customers on average.

Outages occurred during process
During the rotating blackouts in Austin, two outage situations occurred. These outages were caused by equipment failures. The first outage affected an area that extended from Oltorf to the River and from IH-35 to Mopac. The second involved an area from the river, south to Riverside Drive and from Burton to Montopolis. Both outages lasted several hours each. They were not part of the rotating blackouts. These were situations where repairs had to be made in order for power to be restored.

With the exception of the above outages, Austin Energy was generally able to achieve its goal of ensuring that no group of customers disconnected as part of the rotating blackouts were out longer than about 10 minutes at a time.

Austin has sufficient generation
Austin Energy had ample generation to serve our community throughout the statewide shortage April 17th. In fact, during this emergency situation, Austin was supplying up to 200 MW of power to the statewide grid. However, when a shortage of generation occurs statewide, the whole state must participate in restoring the balance. This is because the shortage reduces the frequency of the entire grid. There is no such thing as one section of the grid being stable and the rest unstable. So, until there is sufficient generation available statewide to restore the balance, load shedding is necessary.

Texas has sufficient generation
The rotating blackouts required April 17th were due to extraordinary temperatures for the time of year, power plants undergoing maintenance, and power plant failures. When all generation in Texas is online, the state has a sufficient supply of power. This includes a surplus projected to be about 15% at peak this summer. For that reason, power supplies in Texas are expected to be adequate to meet electric demands throughout the summer.

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For more information, contact Ed Clark, Public Information.
Phone: (512) 322-6514
Pager: (512) 802-2000