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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
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 )
•
ERCOT connections to other grids are limited to
direct current (DC) ties, which allow control over
flow of electricity
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 Wind Installations as of 12.31.12
3
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
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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
Bus 1
Bus 2
Bus 3
Bus 4
Bus 6
Bus 5
ERCOT
WGR
Bus 7
0.69kV
34.5kV
34.5kV
Collector System
69kV
69kV
Point Of Interconnection
Short Circuit Ratio (SCR):
Normal: 3
Outage: Less than 2
Operation Experience
PMU Records
Benchmark
Simulation
Low Wind Output
Low Wind Output
High Wind Output
High Wind Output
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:
–
–
–
–
–
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Dynamic model, tool adequacy
Controller limit: wind turbine, SVC, STATCOM…
System strength enhancement
Protocol requirement (grid code)
Protection challenges
…