4/15/2018 Reliability Planning Review Rio Grande Valley Event Produced by Luminant Energy March 25, 2011

Modeled Load Levels in the Valley 4/15/2018 Modeled Load Levels in the Valley Generation Capacity plus import capacity Planning: 3,181 MW Operations: 2,881 MW Generation Capacity with Largest generator off-line (750 MW ), plus Import Capacity: Planning: 2,431 MW Operations: 2,131 MW Annual load growth runs about 50 MW, however, there is an additional 250 MW load at Loma Alta comes in 2014. Also, graph does not show transmission line losses of ~2%, or ~50 MW. Models show adequate generation and import capacity to serve Valley peak load conditions only when Magic Valley, and other generation is available, along with the planning level of import capability.

Application of Nodal Operating Guide 4/15/2018 Application of Nodal Operating Guide Nodal Operating Guide Section 5.3.2 (actual language): The contingency studies will be performed for reasonable variations of Load level, generation schedules, planned transmission line Maintenance Outages, and anticipated power transfers. At a minimum, this should include projected Loads for the upcoming summer and winter seasons and a five-year planning horizon. The TSPs involved should plan to resolve any unacceptable study results through the provision of Transmission Facilities, the temporary alteration of operating procedures (i.e., RAPs), temporary Special Protection Systems (SPSs), or other means as appropriate. Nodal Operating Guide Section 1.4: Credible Single Contingency (abbreviated language): A single facility. This includes multiple equipment Outaged or interrupted during a single fault (SFME). The Forced Outage of a DCKT in excess of 0.5 miles in length. Any Generation Resource: Combined cycle is a single unit, unless registered as being able to operate combustion turbine and steam turbine seperately. With any single Generation Resource unavailable, and with any other generation preemptively redispatched, the contingency loss of a single Transmission Facility. All normal and contingency conditions outlined in North American Electric Reliability Corporation (NERC) Reliability Standards and any subsequent revisions.

Application of Nodal Operating Guide 4/15/2018 Application of Nodal Operating Guide Questions: What is a “reasonable variation” as it applies to transmission planning studies? How are TO’s applying reasonable variations to transmission planning studies? To what level of prescriptiveness should these reasonable variations be defined to enable affirmative demonstration of NERC/TRE compliance? Prescriptive language (e.g. 1 in 10 yr, or 1 in 20 yr weather) and show completion checkmarks? Leave vague, but describe methods for each project? Other? What variations should be considered? 1 in 10 year peak load levels, 1 in 20 year peak load levels? Historically typical generator de-rates, planned outages, forced outages (State of the Market Report)? Dynamic line ratings correlated to high temperature / high load conditions? How should power transfers be applied? How should operating practices be applied to transmission planning studies, such as the 1400 MW import capacity into the Rio Grande Valley for planning, while operators limit import to 1100 MW? What other planning methods should be considered to meet the “reaonable variations” requirement?

Summer Peak & Temperature correlation Source: March 11, 2011 RPG Meeting presentation on LRGV Import

LRGV Winter Peak & Temperature correlation Source: March 11, 2011 RPG Meeting presentation on LRGV Import

Feb 3, 2011 Load Levels in the Valley 4/15/2018 Feb 3, 2011 Load Levels in the Valley State Estimator Actual 867 MW 49% higher SSWG 11Win1 The February 3, 2011 weather event resulted in a peak load 49% higher than currently modeled in the SSWG 11Win1 Base Case

Next Steps Items to develop recommendations: Load levels : 4/15/2018 Next Steps Items to develop recommendations: Load levels : Weather variability Load growth variability Generation schedules / Power transfersTransmission Derates, Forced Outages, Planned Outages Temperature and Wind driven transfers Transmission: Dynamic ratings associated with weather variability Long-term outages such as autotransformers.