Existing and potential constraints within ERCOT

Austin, Texas

Since Texas opened its electricity market to competition in January 2002, a major part of a successful restructuring operation has been transmission lines–how many there are and if there’s enough transmission capacity to meet changing requirements. That’s where ERCOT comes in, managing the power grid for the state of Texas. In fact, 85 percent of the state’s consumer, business and industrial power customers rely on this power grid to receive electricity.

The ERCOT service area is about 200,000 square miles and includes counties ranging from a population of 67 (Loving County in West Texas) to 3 million (Harris County in Southeast Texas). It represents a bulk electric system located entirely in Texas. ERCOT oversees the operation of approximately 75,000 MW of installed generations and more than 37,000 miles of transmission lines.

The T&D picture

Daily transmission constraints increase electricity costs to consumers, reduce system reliability, and increase the risk of equipment damage. Two types of constraints are defined in the ERCOT market: commercially significant constraints (CSCs) limit the flow of energy from one of the four major zones in the ERCOT region into another, and local constraints (LCs) limit the flow of energy in areas within a zone in ERCOT.

Reducing transmission constraints is essential to ensuring reliable and affordable electricity–now and in the future.

The following are CSCs in ERCOT for 2003:

  • West Texas to North Texas (Primary corridor is Morgan Creek to Abilene to Graham to Parker.);
  • South Texas to North Texas (Primary corridor is Marion to Zorn to Austrop to Sandow to Temple to Waco to Venus.);
  • South Texas to Houston (Primary corridor is Corpus Christi to South Texas Project to Houston).

The following are the most significant LCs in ERCOT for 2003:

  • Dallas/Fort Worth,
  • Corpus Christi,
  • Laredo,
  • Rio Grande Valley,
  • West Texas (McCamey, San Angelo, Morgan East, and wind farms).

Transmission congestion costs to ERCOT consumers totaled more than $250 million between July 31, 2001, and May 31, 2002. These costs could have been even greater due to factors not included in the overall report, such as increased risk of service interruptions that could result from transmission constraints and the use of plants that are less efficient and cause more pollution to relieve the congestion.

New generation could lead to more problems

Since 1997, ERCOT has received more than 170 system evaluation requests from across the state from entities that want to build new generation capacity in ERCOT. Load growth in the state, revisions to the PUCT transmission rules, and market deregulation are attracting merchant plant developers to the Texas market. Proposed new generation may help relieve the current transmission constraints in ERCOT, depending on the proposed location, but it may also worsen the constraints because the existing transmission system cannot fully accommodate the proposed new plants.

Transmission planning is based on dealing with uncertainty. Factors that give rise to uncertainty include whether proposed generating plants will actually be built and which power plants will reduce their output or be taken out of service because of competition from newer, more efficient generating plants. These and the operating uncertainties mean that planning for any new transmission additions should provide for a robust transmission system that can deal with a variety of future conditions.

ERCOT, along with transmission service providers, is planning necessary transmission to maintain reliable service and to address transmission bottlenecks. The following major projects identified in past ERCOT reports have been completed:

  • Limestone-Watermill 345-kV double-circuit line,
  • Monticello-Farmersville 345-kV line,
  • Lon Hill-Rio Hondo and Lon Hill-Edinburgh 345-kV lines series capacitor compensation,
  • Military Highway STATCOM,
  • Laredo STATCOM,
  • San Miguel-Pawnee 345-kV line and establish Pawnee 345-kV station,
  • Centerville Switch-McCree Switch 345-kV line,
  • White Point 345-kV switching station and 138-kV upgrades,
  • Cedar Bayou-King-North Belt-TH,Wharton 345-kV corridor upgrades,
  • Various 138-kV and 69-kV system additions/upgrades, including autotransformers.

ERCOT has also supported and recommended the following major projects, currently under development by transmission service providers, which will help further mitigate constraints:

  • Morgan Creek-Twin Buttes-Red Creek-Comanche Switch 345-kV line,
  • Graham-Jacksboro 345-kV line,
  • Pawnee-Coleto Creek 345-kV line,
  • Farmersville-Valley Junction-Anna Switch 345-kV line,
  • Paris-Anna 345-kV line,
  • Venus-Liggett 345-kV line,
  • Edinburg-Bates-McAllen 345-kV line,
  • McAllen-Brownsville-La Palma 345-kV line,
  • Various 138-kV and 69-kV system additions/upgrades including autotransformers.

ERCOT is also leading three regional planning groups to determine additional actions needed to serve load and continue to resolve transmission constraints.

What does this mean for Texas? Briefly stated, Texas’ power delivery infrastructure is in excellent condition in comparison to other states. It also means, however, that more transmission lines are needed to effectively move power around the state to meet the demand. Most of these additional transmission facilities would be needed whether or not Texas had chosen to restructure its market.

The good news is that Texas has plenty of power to meet the state’s needs. For example, there are just three power grids in the U.S.: the Western Interconnect, the Eastern Interconnect and Texas. Because Texas has its own grid, it is not dependent on imported energy. Some states, including California, must import power from hydroelectric plants in Oregon, Nevada and elsewhere. It’s also easier to build needed transmission facilities in Texas. The projects listed above represent ERCOT’s continuing efforts to increase the likelihood that power will flow easily around the state.

Electric use is continuing to grow, reflecting the transformation of our economy to a high-technology information base that relies on electricity. Electricity, though, is not a commodity that can be easily stored, and our transmission infrastructure is at the heart of our economic well-being. An open, coordinated transmission planning process that incorporates transmission upgrades to relieve constraints, unwavering reliability requirements, and the interconnection of new supply (including environmentally-friendly units) will be of paramount importance to the future of Texas.

More information can be found at ERCOT’s Web site www.ercot.com.

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The Clarion Energy Content Team is made up of editors from various publications, including POWERGRID International, Power Engineering, Renewable Energy World, Hydro Review, Smart Energy International, and Power Engineering International. Contact the content lead for this publication at Jennifer.Runyon@ClarionEvents.com.

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