Lone Star Transmission Presentation on SSR

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

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

3. History of Lone Star and CREZ • 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

4. Lone Star Transmission System 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

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

6. Fort Worth – Dallas West Shackleford Scurry County South Abilene Romney Series Compensation Sam Switch Navarro Kopperl Series Compensation

7. Sub-Synchronous Resonance (SSR) • 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

8. Mitigating the Effects of SSR 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™/D10Draft Guide for the Specification of Fixed Series Capacitor Banks for Transmission System Applications

9. Lone Star Transmission Coordination & Mitigation • 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

10. Questions? Thank you