1. Lone Star Transmission Presentation on SSR Blair Giffin Operations Engineer September 9, 2013

2. 2 History of Lone Star and CREZ Lone Star Transmission System Sub-Synchronous Resonance (SSR) Mitigating the effects SSR Lone Star Transmission Coordination & Mitigation Topics

3. 3 In 2008 ERCOT performed the CREZ Transmission Optimization Study (CTOS) that included 4 build-out options PUCT selected a 345kV build-out option, including series- compensated lines PUCT selected Lone Star Transmission to build series- compensated West Shackelford to Sam Switch/Navarro (and Scurry County South – West Shackelford) ERCOT commissioned ABB to perform the CREZ Reactive Compensation Study that verified amounts of series compensation and sized additional reactive devices History of Lone Star and CREZ

4. 4 Lone Star Transmission 345 kV Circuits With Series Compensation ‒ Navarro – W. Shackelford 345kV Line ‒ Sam Switch – W. Shackelford 345kV Line Without Series Compensation ‒ West Shackelford - Scurry County South 345 kV Line 1 ‒ West Shackelford - Scurry County South 345 kV Line 2 Lone Star Transmission 345 kV Substations West Shackelford Switching Station Kopperl Series Compensation Station Romney Series Compensation Station Navarro Switching Station Sam Switch Switching Station Lone Star Transmission System

5. 5 Scurry County South West Shackelford Kopperl Series Compensation Station Clear Crossing Romney Series Compensation Station Ties to Existing Grid Sam Switch Navarro Ties to Existing Grid Lone Star Transmission System

6. 6 Fort Worth – Dallas Abilene

7. 7 SSR is an interaction between series capacitors and torsional frequencies of turbine-generator rotors SSR was studied in 1937 when The General Electric Company noticed oscillations in distribution systems with series capacitors 1970 – Mohave generating plant in Nevada experienced turbine-generator interaction To date, numerous series-compensated transmission systems have been designed, installed and safely operated Sub-Synchronous Resonance (SSR)

8. 8 Several proven methods exist for mitigating the effects of SSR* (some methods do not apply to every capacitor type) Switching of series capacitors (by-passing) or limiting the total amount of compensation SSR blocking filters Supplemental exciter damping controls (SEDC) Thyristor-controlled series capacitor (TCSC) Dynamic stabilizer at generator * IEEE P1726™/D10 Draft Guide for the Specification of Fixed Series Capacitor Banks for Transmission System Applications Mitigating the Effects of SSR

9. 9 Lone Star Transmission is working with ERCOT and Transmission Owners –SSR Studies –Outage Coordination to reduce potential SSR –Operational mitigation plans Lone Star Transmission has: –Developed situational awareness tools that identify ERCOT transmission conditions (line outages) that increase the potential for SSR –Implemented switching procedures to by-pass series capacitors, mitigating the potential for SSR Lone Star Transmission Coordination & Mitigation

10. 10 Questions? Thank you