Review of TADS Data for 2012 Voltage Class Name Metric AC Transmission Outages - Failed Protection System Equipment AC Transmission Outages - Human Error AC Transmission Outages - Failed AC Substation Equipment AC Transmission Outages - Failed AC Circuit Equipment AC Transmission Outages - Lightning AC Transmission Outages - Contamination AC Transmission Outages - Foreign Interference Total Element Availability Percentage (APC) Transmission System Unavailability AC Circuit kV Outages per Circuit AC Circuit kV Outages per 100 miles per year kVJan-12Dec-12 # Circuits Circuit Miles Multi-circuit Structure Miles Automatic Outages Circuit Data Outage InformationCountDuration (hrs) Automatic Non-Automatic Outage Data Outage InformationCount Duration (hrs) Two Elements94.82 Three Elements35.3 Four or More Elements118.3 Multiple Element Automatic Outages

Review of TADS Automatic Outage Data for 2012 ●Lightning, Contamination, and Unknown represent 73% of all momentary outages ●Momentary and Sustained automatic outages by month for 2012

Review of TADS Automatic Outage Data for 2012 ●Failed AC Substation Equipment represented 22% of sustained outage cause vs. 46% of sustained outage duration ●Failed AC Circuit Equipment represented 7% of sustained outage cause vs. 16% of sustained outage duration

Review of TADS Planned Outage Data for 2012

●55% of planned outage duration ranges from two to 24 hours ●37% of planned outage duration is greater than 24 hours

TADS Comparison, 2011 vs Outage InformationCountDuration (hrs)CountDuration (hrs) Automatic Non-Automatic Voltage Class kV MetricOutages/Number of circuitsOutages/100 mi/year AC Transmission Outages - Failed Protection System Equipment AC Transmission Outages - Human Error AC Transmission Outages - Failed AC Substation Equipment AC Transmission Outages - Failed AC Circuit Equipment AC Transmission Outages - Lightning AC Transmission Outages - Contamination AC Transmission Outages - Foreign Interference Total Element Availability Percentage (APC) Transmission System Unavailability

TADS Comparison,

TADS Comparison, April-May 2011 had higher than normal rate of contamination-related outages due to ongoing drought issues Sept 2011 had high sustained outage duration due to wildfires

Common Mode and Dependent Mode Outage Statistics Dependent Mode outages (defined as an automatic outage of an element which occurred as a result of another outage) Common Mode outages (defined as one or more automatic outages with the same initiating cause and occur nearly simultaneously) In 2012, represented 6.0% of all momentary outages, 26.3% of all sustained outages (6.6% of sustained outage duration), and 13.0% of all automatic outages.

NERC Adequate Level of Reliability (ALR) Metrics MetricDefinitionERCOT Metric NERC Metric ERCOT Metric NERC Metric ERCOT Metric NERC Metric ALR6-11Automatic Outages Initiated by Failed Protection Equipment 4.95%6.26%3.05%5.55%2.62%5.07% ALR6-12Automatic Outages Initiated by Human Error 1.41%6.57%6.77%6.87%4.26%6.55% ALR6-13Automatic Outages Initiated by Failed AC Substation Equipment 8.13%5.59%13.2%8.14%5.89%6.19% ALR6-14Automatic Outages Initiated by Failed AC Circuit Equipment 2.83%5.89%5.08%5.37%4.58%4.78% ALR6-15Element Availability Percentage 98.64%98.41%98.06%97.86%98.62%97.89% Comparison of ERCOT to NERC metrics for Adequate Level of Reliability measurements