© ABB Group April 20, 2011 | Slide 1
Dynamic Studies for Large Scale Renewable
Energy Integration
ERCOT CREZ Case Study
ABB Automation & Power World: April 18-21, 2011
© ABB Group April 20, 2011 | Slide 2© ABB Inc. April 20, 2011 | Slide 2
CPS-109-1
Dynamic Studies for Large Scale Renewable Energy Integration
ERCOT CREZ Case Study
Speaker name: Don Martin
Company name: ABB Grid System
Consulting
Location: Raleigh, NC
Speaker name: Ken Donoho
Company name: ONCOR
Location: Dallas, TX
© ABB Group April 20, 2011 | Slide 3© ABB Inc.April 20, 2011 | Slide 3
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© ABB Group April 20, 2011 | Slide 4© ABB Inc.April 20, 2011 | Slide 4
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Identify the meeting room your workshop is being held in
Locate the nearest exit
© ABB Group April 20, 2011 | Slide 5
ERCOT CREZ Reactive Study Overview
A large-scale, complex study to
determine the reactive
compensation needs for the
CREZ transmission
Both shunt and series reactive
compensation considered
Ambitious goals and schedule
Excellent support from ERCOT
and the Transmission Service
Providers
© ABB Group April 20, 2011 | Slide 6
ERCOT CREZ Reactive Study Overview
Double Ckt
Single Ckt
CREZ 345-kV
System
© ABB Group April 20, 2011 | Slide 7© ABB Group April 20, 2011 | Slide 7
ERCOT CREZ Reactive Study Overview
The PUCT-selected plan includes
Long 345kV AC circuits (mostly double circuits) with
the sole purpose of integrating the proposed
asynchronous generation
Nine circuits were designed with 50% series
compensation
“Place holder” shunt compensation were included in
the plan, with a recommendation for additional study
Study objectives
Verify or correct ratings and percentage of proposed
series compensation
Identify size, type and location of additional reactive
devices required to control system voltages and
maintain dynamic stability
Identify stability-related issues
CREZ 345-kV
System
© ABB Group April 20, 2011 | Slide 8© ABB Group April 20, 2011 | Slide 8
ERCOT CREZ Reactive Study Results
Results for Initial Wind of 16,200 MW
Study plan modifications included:
New 345-kV Substation with 8 lines by looping in 4
lines – Needed for dynamic stability performance
Ultimately 12 circuits were designed with 50% series
compensation
Study Results Identified:
3,930 MVARS Shunt Reactors
1,860 MVARS of Shunt Capacitors
Total SVC capacity of +1,400 MVARS / -450 MVARs
© ABB Group April 20, 2011 | Slide 9© ABB Group April 20, 2011 | Slide 9
ERCOT CREZ Reactive Study Results
Results for Ultimate Wind of 20,375 MW
Study plan modifications included:
Synchronous Condensers to increase short circuit
strength in Panhandle in order to operate wind
turbines (2 x 350 MVA)
Study Results Identified:
276 Additional MVARS of Shunt Capacitors
Additional SVC capacity of +3,900 MVARS / -1,300
© ABB Group April 20, 2011 | Slide 10
ERCOT CREZ Reactive Study Results
SUMMARY OF REACTIVE POWER REQUIREMENTS
TOTAL REQUIREMENT
Min Export Initial Build Max Export/Edison
Series Capacitor 50% - 12 Lines 50% - 12 Lines 50% - 12 Lines
Shunt Reactors 3930 MVArs 3930 MVArs 3930 MVArs
Shunt Capacitors 0 860 MVARs 1136 MVARs
SVCs or STATCOMs: 0 1400 MVARs 5300 MVArs
Synchronous Condensers 0 0 700 MVA
© ABB Group April 20, 2011 | Slide 11© ABB Group April 20, 2011 | Slide 11
CREZ Reactive Power StudyResults
To address the study objectives several areas were evaluated including
Coordinate System Performance Criteria
Fundamental frequency concerns
Conventional powerflow
Optimal powerflow
Dynamic stability
Chronological loading analysis
Sub-synchronous concerns
SSI (wind generators and series capacitors)
SSR (thermal generators and series capacitors)
SSTI (thermal generators and dynamic shunt VAR sources)
© ABB Group April 20, 2011 | Slide 12
ERCOT CREZ Reactive Study Results
SYSTEM SHUNT LINE REACTOR REQUIREMENTS FOR ENERGIZING
LINES
1. Lines between 140 miles and 200 miles a 50 MVAr shunt line reactor will be needed
to limit the line voltage to less than 1.10 pu at the open end.
2. Lines over 200 miles a shunt reactor of 100 MVARs will be required to limit the line
voltage to 1.10 pu.
1.000
1.025
1.050
1.075
1.100
1.125
1.150
0 10 20 30 40 50 60 70 80 90 100
% Line Length from Sending End
Vo
ltag
e [
pu
]
50 MVAR reactor 100 MVAR reactor
Line voltage profile for 215 mi. line, 50 or 100 MVAr reactor at open end
© ABB Group April 20, 2011 | Slide 13
ERCOT CREZ Reactive Study Results
LINE VOLTAGE PROFILES TO ASSIST IN OPTIMUM LOCATION FOR
SERIES CAPACITORS
0.9
0.95
1
1.05
1.1
1.15
1.2
0 20 40 60 80 100
% Line Length from Receiving End
Vo
lta
ge
[p
u]
Mid Line Caps Sending End Caps
1000MW
LINE VOLTAGE PROFILES FOR LINES WITH SERIES CAPACITORS AT THE END AND MIDDLE OF A LINE
© ABB Group April 20, 2011 | Slide 14
ERCOT CREZ Reactive Study Results
REQUIREMENTS FOR RATING THE SERIES CAPACITOR BANKS
Rated capacitor reactive impedance (ohms)
Continuous capacitor current requirements (amperes)
30 minute overload current requirements (amperes)
Maximum swing current following system disturbances
Maximum fault current for external faults
Maximum fault current for internal faults
© ABB Group April 20, 2011 | Slide 15
ERCOT CREZ Reactive Study Results
REQUIREMENTS FOR RATING THE SHUNT CAPACITOR BANKS AND
REACTOR BANKS
Largest MVAR that can be switched at each station
Estimate of number of switching (breaker open and close)
operations per year
© ABB Group April 20, 2011 | Slide 16
ERCOT CREZ Reactive Study Results
SYSTEM UNBALANCE SIMULATIONS
Voltage Unbalance
Negative Sequence Generator Currents
CAB
CAB
CCAABB
BCA
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CAB
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CCAABB
ABC
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CC A
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AAB
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CAB
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BCA
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ABC
AABBCC
CAB
CCAABB
BCA
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BCA
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ABC
AABBCC
CAB
CCAABB
BCA
BBCCAA
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A
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CCA
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ABC
AABBCC
© ABB Group April 20, 2011 | Slide 17
ERCOT CREZ Reactive Study Results
DYNAMIC SHUNT REACTIVE POWER
SVC and STATCOM both can provide the needed dynamic MVARs
General evaluation modeled units of +300 / -100 MVAR SVC
Dynamic MVARs identified to prevent voltage collapse following
faults and loss on lines
© ABB Group April 20, 2011 | Slide 18
ERCOT CREZ Reactive Study Results
SHORT CIRCUIT REQUIREMENTS
For high wind generation, control oscillations occurred in the
WTG models in the Panhandle areas
WTGs have minimum short circuit operating levels and may vary
with type and manufacturer
Study solutions was to add two 350 MVA synchronous
condensers
Sync Condenser can use some MVAR for steady-state reactive power control
Sync Condenser can reserve some MVAR for dynamic voltage recovery
© ABB Group April 20, 2011 | Slide 19© ABB Group April 20, 2011 | Slide 19
CREZ Reactive Power StudyResults
To address the study objectives several areas were evaluated including
Coordinate System Performance Criteria
Fundamental frequency concerns
Conventional powerflow
Optimal powerflow
Dynamic stability
Chronological loading analysis
Sub-synchronous concerns
SSI (wind generators and series capacitors)
SSR (thermal generators and series capacitors)
SSTI (thermal generators and dynamic shunt VAR sources)
© ABB Group April 20, 2011 | Slide 20
CREZ Reactive Power Study
Subsynchronous Interactions
Sub-synchronous concerns
SSI - wind generators (4 types) and series capacitors
Type 1 Induction Generator
Type 2 Variable Resistor Induction Generator
Type 3 Doubly Fed Induction Generator (DFIG)
Type 4 Full Back-to-back Converters
© ABB Group April 20, 2011 | Slide 21
CREZ Reactive Power Study
Subsynchronous Interactions
SSI with each type of wind generators with series
capacitors
Classical self-excitation of induction machines possible for Type 1
and Type 2 machines near series-compensated lines
Type 3 machines near series-compensated lines found to be quite
sensitive to subsynchronous interactions.
Type 4 machines not found in this study to have issues
© ABB Group April 20, 2011 | Slide 22
ERCOT CREZ Reactive Study Results
SUMMARY OF SSI
Problems for WTG Type 1 on CREZ System – Self Excitation
Main : Graphs
0.0 2.5 5.0 7.5 10.0 12.5 15.0 17.5 20.0 ...
...
...
-1.50
-1.00
-0.50
0.00
0.50
1.00
1.50
y (k
V)
Vl2n_WF1GSUs_kV
Main : Graphs
0.0 2.5 5.0 7.5 10.0 12.5 15.0 17.5 20.0 ...
...
...
-4.0k
-3.0k
-2.0k
-1.0k
0.0
1.0k
2.0k
3.0k
y (k
A)
Iph_WF1GSUs_kA
Series Capacitors Inserted into the Radial Low
Resistance System at 4.0 seconds
© ABB Group April 20, 2011 | Slide 23
ERCOT CREZ Reactive Study Results
SUMMARY OF SSI
Problems for WTG Type 3 on CREZ System – Control Interaction
Series Capacitors Inserted into the Radial System at 4.0
secondsMain : Graphs
0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 ...
...
...
-8.0
-4.0
0.0
4.0
8.0
y (k
A)
Iph_WF1GSUs_kA
-0.80
-0.40
0.00
0.40
0.80
y (k
V)
Vl2n_WF1GSUs_kV
-0.60
-0.30
0.00
0.30
0.60
y (k
A)
Iph_SC_kA
-400
-200
0
200
400
y (k
V)
Vl2n_SC_kV
-60
-40
-20
0
20
40
60
y (k
V)
Vinst_SC_kV
Main : Graphs
0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 ...
...
...
-8.0
-4.0
0.0
4.0
8.0
y (k
A)
Iph_WF1GSUs_kA
-0.80
-0.40
0.00
0.40
0.80
y (k
V)
Vl2n_WF1GSUs_kV
-0.60
-0.30
0.00
0.30
0.60
y (k
A)
Iph_SC_kA
-400
-200
0
200
400
y (k
V)
Vl2n_SC_kV
-60
-40
-20
0
20
40
60
y (k
V)
Vinst_SC_kV
Main : Graphs
9.800 9.820 9.840 9.860 9.880 9.900 9.920 9.940 9.960 9.980 10.000 ...
...
...
-8.0
-4.0
0.0
4.0
8.0
y (k
A)
Iph_WF1GSUs_kA
-0.80
-0.40
0.00
0.40
0.80
y (k
V)
Vl2n_WF1GSUs_kV
-0.60
-0.30
0.00
0.30
0.60
y (k
A)
Iph_SC_kA
-400
-200
0
200
400
y (k
V)
Vl2n_SC_kV
-60
-40
-20
0
20
40
60
y (k
V)
Vinst_SC_kV
Main : Graphs
9.800 9.820 9.840 9.860 9.880 9.900 9.920 9.940 9.960 9.980 10.000 ...
...
...
-8.0
-4.0
0.0
4.0
8.0
y (k
A)
Iph_WF1GSUs_kA
-0.80
-0.40
0.00
0.40
0.80
y (k
V)
Vl2n_WF1GSUs_kV
-0.60
-0.30
0.00
0.30
0.60
y (k
A)
Iph_SC_kA
-400
-200
0
200
400
y (k
V)
Vl2n_SC_kV
-60
-40
-20
0
20
40
60
y (k
V)
Vinst_SC_kV
© ABB Group April 20, 2011 | Slide 24
ERCOT CREZ Reactive Study Results
SUMMARY OF SSI
Problems for WTG Type 3 on CREZ System
• SSI at one site with no contingencies
• SSI at one site with one uncompensated line out
• SSI at one site with loss of the double circuit lines to Scurry
© ABB Group April 20, 2011 | Slide 25
ERCOT CREZ Reactive Study Results
SUMMARY OF SSR with Thermal Units
Completed SSR Screening Study
• Calculated subsynchronous damping from 1 – 60 Hz
• Identified negative damping modes and frequency of negative modes
• Compare negative modes with generator shaft modes
0 10 20 30 40 50 60-2
-1.5
-1
-0.5
0
0.5
1Example SSR screening
Ele
c.
Dam
p.
Coeff
. [p
u]
Torsional Freq. [Hz]
NL
FL
NL
FL
NL
FL
NLFL
NL
FL
NL
FL
NL
FL
NLFL
© ABB Group April 20, 2011 | Slide 26
ERCOT CREZ Reactive Study Results
SUMMARY OF SSR with Thermal Units
SSR Screening Study Results
Three generating station may begin to see initial indications of SSR with 4 or
more outages.
One generating station has initial indications with 2 or more outages
Some locations may have negative damping but torsional modes of the units
must be checked to verify whether resonances may be an issue
© ABB Group April 20, 2011 | Slide 27
ERCOT CREZ Reactive Study Results
SUMMARY OF SSI
Transmission Solutions for SSI and SSR
• TCSC
• Preventive Bypass Filter
• Modify WTG Controls
© ABB Group April 20, 2011 | Slide 28
ERCOT CREZ Reactive Study Results
Thyristor Controlled Series Capacitor (TCSC)
Thyristor fires with controlled timing
Current circulates to “boost” capacitor voltage
Larger effective capacitance at fundamental frequency
+ uC -
iL iC
iV
© ABB Group April 20, 2011 | Slide 29
ERCOT CREZ Reactive Study Results TCSC impedance characteristics
© ABB Group April 20, 2011 | Slide 30
ERCOT CREZ Reactive Study Results
Preventive Bypass Filter was simulated
Developed solution to damp SSI
Technical feasibility not completely demonstrated and cost to be high
Csc
Cf
LfRL
Rd
ILf
ICf
If
ISC
© ABB Group April 20, 2011 | Slide 31
ERCOT CREZ Reactive Study Results
Control modifications was not simulated – proprietary manufacturer
Test results of a wind farm with modified controls shown below
Testing for SSI for a Type 3 DFIG Wind Farm with Modified controls
Scale: 10 Amps and 120 Hz
1 Amp 35 Hz
2 Amps 12 Hz
© ABB Group April 20, 2011 | Slide 32
ERCOT CREZ Reactive Study General Plan
Address scope in four
phases
I – Initial reactive
compensation
verification
II – Sub-
synchronous
Interaction (SSI)
evaluation
III – Reactive
compensation
refinement
IV – Finalize and
compile equipment
requirements
PHASE I
PHASE III
PHASE II
INITIAL REACTIVE
COMPENSATION
VERIFICATION
GENERAL
SSI
EVALUATION
SPECIFIC
SSI
EVALUATION
REACTIVE
COMPENSATION
REFINEMENT
PHASE IV
REACTIVE
COMPENSATION
EQUIPMENT
REQUIREMENTS
© ABB Group April 20, 2011 | Slide 33
ERCOT CREZ Reactive Study General Appearance
Address scope in four
phases
I – Initial reactive
compensation
verification
II – Sub-
synchronous
Interaction (SSI)
evaluation
III – Reactive
compensation
refinement
IV – Finalize and
compile equipment
requirements
PHASE I
PHASE III
PHASE II
INITIAL REACTIVE
COMPENSATION
VERIFICATION
GENERAL
SSI
EVALUATION
SPECIFIC
SSI
EVALUATION
REACTIVE
COMPENSATION
REFINEMENT
PHASE IV
REACTIVE
COMPENSATION
EQUIPMENT
REQUIREMENTS
© ABB Group April 20, 2011 | Slide 34© ABB Inc.April 20, 2011 | Slide 34
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