Page 1ERCOT Project Status

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ERCOT Dynamic Ratings

METF

March 29, 2012

Page 2ERCOT Project Status

Conceptual Model

ProcessedRatings

ICCP

WeatherForecast

Data

Dynamic RatingsApplication

SCADA

Portal

StaticTable

RawRatings

Weather Bank

Real TimeNetwork

Applications

Real Time MarketClearance Engine

Day AheadStudies

Page 3ERCOT Project Status

Dynamic Ratings – Weather Stations and Zones

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Dynamic Ratings Weather Stations to Zone Mapping

Weather Zone Station 1 Station 2 Station 3

North Central 50% -- Dallas 25% -- Waco 25% -- Mineral Wells

East 50% -- Tyler 50% -- Lufkin

North 50% -- Witchita Falls 50% -- Paris

Far West 50% -- Wink 50% -- Midland

West 40% -- Abeline 40% -- San Angelo 20% -- Junction

South Central 50% -- Austin 50% -- San Antonio

Coast 50% -- Houston 30% -- Galveston 20% -- Victoria

Southern 40% -- Corpus Christi 40% -- Brownsville 20% -- Lardeo

Page 5ERCOT Project Status

Dynamic Ratings – Real Time Process

• Ratings may be supplied via ICCP. Three ratings (normal, emergency, and 15 minute) must be submitted for each line.

• If ICCP data is not supplied or if ICCP is currently unavailable, ratings from a standard table mapped to temperatures are used.

• Updates are made in near real-time and applied to SCED

• For jointly-owned lines, the most conservative value will be used.

Page 6ERCOT Project Status

Dynamic Ratings Project – Look Ahead Process

• All lines have static temperature versus ratings tables defined by the owning TSP.

• All lines use the forecasted temperature of a nearby weather station (or weather zone temperature), as assigned by the TSP.

• ERCOT uses its 168hr weather station forecast data updated hourly by the weather vendor for both load forecasting and dynamic ratings.

• The resulting temperature-adjusted ratings are used for all RUC and manual future studies performed on the power system network.

• For jointly-owned lines or for lines that cross multiple weather stations, the most conservative value will be used.