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Connection of Wind Farms to Weak AC networks – ERCOT Experience and Challenges

Connection of Wind Farms to Weak AC networks – ERCOT Experience and Challenges Shun- Hsien (Fred) Huang ERCOT System Planning CIGRE WG B4.62 Meeting June 5 th , 6 th , 2013. ERCOT Quick Facts. Electric Reliability Council of Texas – the ERCOT grid: Covers 75% of Texas land

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Connection of Wind Farms to Weak AC networks – ERCOT Experience and Challenges

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  1. Connection of Wind Farms to Weak AC networks – ERCOT Experience and Challenges Shun-Hsien (Fred) Huang ERCOT System Planning CIGRE WG B4.62 Meeting June 5th, 6th, 2013

  2. ERCOT Quick Facts • Electric Reliability Council of Texas – the ERCOT grid: • Covers 75% of Texas land • Serves 85% of Texas load • >40,000 miles of transmission lines • >550 generation units • Peak Load: 68,379 MW (Aug 3, 2011 ) • Wind Integration • Wind capacity: ~10,500 MW • Includes ~2,000 MW in coastal area • Wind generation record: 9,418 MW (Feb. 23, 2013), 28 percent of load at the time ERCOT connections to other grids are limited to direct current (DC) ties, which allow control over flow of electricity

  3. ERCOT Wind Installations as of 12.31.12

  4. Competitive Renewable Energy Zone (CREZ) • Deliver wind power from remote region to the load centers through long extra high voltage transmission lines. • Located at remote region, far away from synchronized generators and load. • Significant power electronic devices to provide system support. • Weak Grid • Low short circuit ratio (SCR) • Voltage will not be stiff, challenge for voltage control (steady state and dynamic) • System performance is dominated by high wind/low wind, not summer peak/winter off-peak

  5. Planning Studies: High Wind Scenario (a). Without applying high voltage ride though capability. (b). Applying limited high voltage ride through capability. Fig. Voltage response at a 345kV bus in CREZ

  6. Cause and Potential Solutions • Cause: Weak Grid • Low short circuit ratio (SCR) • Result in unstable voltage control (faster closed-loop voltage control) • Result in temporary overvoltage that can lead to high voltage collapse • Potential solutions • Controller tuning • Enhance the system strength

  7. Operation Experience Short Circuit Ratio (SCR): Normal: 3 Outage: Less than 2

  8. Operation Experience PMU Records Benchmark Simulation Low Wind Output Low Wind Output High Wind Output High Wind Output

  9. Challenges and Discussions • A significant increase of wind projects proposed to connect to Panhandle area after CREZ implementation. • Short circuit ratio can be less than 1.5 • Challenges: • Dynamic model, tool adequacy • Controller limit: wind turbine, SVC, STATCOM… • System strength enhancement • Protocol requirement (grid code) • Protection challenges • …

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