Connection of Wind Farms to Weak AC networks – ERCOT Experience and ChallengesShun-Hsien (Fred) HuangERCOT System Planning CIGRE WG B4.62 MeetingJune 5th, 6th, 2013

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

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ERCOT Wind Installations as of 12.31.12

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• 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

Competitive Renewable Energy Zone (CREZ)

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

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

Operation Experience

WGR

0.69kV 34.5kV 34.5kV 69kV 69kV

Point Of Interconnection

ERCOT

Collector System

Bus 1 Bus 2 Bus 3 Bus 4 Bus 5 Bus 6

Bus 7

Short Circuit Ratio (SCR):Normal: 3Outage: Less than 2

Operation Experience

Low Wind Output

High Wind Output

Low Wind Output

High Wind Output

PMU Records Benchmark Simulation

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– …