Lone Star Transmission Presentation on SSR

Blair Giffin

Operations Engineer

September 9, 2013

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

• 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

Lone Star Transmission 345 kV Circuits• With Series Compensation

Navarro – W. Shackelford 345kV Line

Sam Switch – W. Shackelford 345kV Line

• Without Series CompensationWest 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

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

Fort Worth – Dallas

Abilene

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

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

Mitigating the Effects of SSR

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

Questions?

Thank you