lessons learned from the texas synchrophasor … learned from the texas synchrophasor network by...
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Lessons Learned from the Texas Synchrophasor Network
by
Presented at the
SWEDE 2011 Annual Conference
Bastrop, TX
Wednesday, April 27, 2011
Prof. W. Mack GradyDept. of Electrical & Computer Engineering
U.T. Austin
Page 1 of 44
Why are SynchrophasorsImportant?
Here’s All You Need to Remember
Average Power Flow P Through a Mostly Inductive Transmission Line (138kV and above)
)sin( 2121 δδ −=XVVP
11 δ∠V 22 δ∠V
jX
+
+
ground
These are about 1pu
For small x, sin(x) = x
Charles Steinmetz, developed phasortheory to analyze
AC circuits
Page 2 of 44
UT Pan Am
Austin
McDonald Observatory
400 miles
300 miles
Implementation and Application of anIndependent Texas Synchrophasor Network
Monitoring 120V Wall Outlet Voltages and Communicating Through the Public Internet
Austin
Majority of load is in the green rectangles, i.e. “Central ERCOT”
120V wall outlet at U.T. Austin, and 69kV 3Φmonitor at nearby Austin Energy Harris Sub
Wind Country
• Funding provided by EPRI
• Equipment provided by Schweitzer Engineering Labs
Page 3 of 44
Bus 2DFW
Bus 4SA
Bus 5VAL
Bus 6COAL
Bus 7WIND
300 km
250 km
150 km300 km
400 km
500 km400 km
Bus 3UT
Bus 1HOU
Positive-sequence line constants for each 345kV circuit:
• R = 0.06 Ω/km per conductor
• L = 1 µH/m
• C = 12 pF/m
• Rating = 800 A per conductor
• From the L, XL (500 km) = 188.5 Ω
• For 345 kV, 100 MVA base, Zbase = 1190 Ω
• For each 500 km circuit, XL = 0.158 pu
• Thus, four parallel circuits have XL = 0.040pu, and six parallel circuits have XL = 0.026 pu
Relatively small phase angle variation in central ERCOT
McDonald Observatory
PMU
UT Austin PMU
Bus 2DFWBus 2DFW
Bus 4SA
Bus 4SA
Bus 5VAL
Bus 5VAL
Bus 6COALBus 6COAL
Bus 7WINDBus 7WIND
300 km
250 km
150 km300 km
400 km
500 km400 km
Bus 3UT
Bus 3UT
Bus 1HOUBus 1HOU
Positive-sequence line constants for each 345kV circuit:
• R = 0.06 Ω/km per conductor
• L = 1 µH/m
• C = 12 pF/m
• Rating = 800 A per conductor
• From the L, XL (500 km) = 188.5 Ω
• For 345 kV, 100 MVA base, Zbase = 1190 Ω
• For each 500 km circuit, XL = 0.158 pu
• Thus, four parallel circuits have XL = 0.040pu, and six parallel circuits have XL = 0.026 pu
Relatively small phase angle variation in central ERCOT
McDonald Observatory
PMU
UT Austin PMU
U.T. Pan AmPMU
Synchrophasor Homework Network for ERCOT
U.T. McDonald ObservatoryPMU
Oscilloscope View. If UT Austin = 0º ref, then McD leads by 60º, and Pan Am lags by 30º
360º
+60º −30º
Small oscillations in the relative phase angles give an indication grid stability. Essentially, these oscillations provide an “EKG” for large power grids.
Page 4 of 44
Our First Remote Phasor Measurement Unit, UT Austin’s McDonald Observatory, in the Attic of the Fire Station
Living is good at the Astronomers’ Lodge
Page 5 of 44
Grady, Brooks, NREL, 1/27/11 6
WECC Grid - The Cloudcroft, NM, (near White Sands National Monument, but 4000’higher in elevation). Long way from Pullman. Doorknob-sized GPS antenna mounted
on a PVC pipe and Christmas tree Stand. Two views of antenna.
LOCATION
Latitude Longitude AltitudeN 32.52.54 W 105.39.10 7583 feet
Satellite Signal Strengths (Min for Lock, 3 Sats > 3.0)12.0 ; 7.0 ; 5.2 ; 6.0 ; 3.6 ; 5.2 ; 1.8 ; 15.2 ; -.- ; -.- ; -.- ; -.-
Page 6 of 44
7
The Cloudcroft, NM, Station, Piggy-Backed onto Standard DSL Internet Service
“The Grid Monitor”(a power strip)
Cloudcroft
GPS ReceiverSpare Antenna
SEL 421 Relay/PMU
DSL Modem and Wireless Router
Page 7 of 44
The Good News and the Bad News
The good news – each remote PMU streams back via internet
• 30 readings per second, • times 60 seconds per minute, • times 60 minutes per hour, • times 24 hours per day,
which equals 2.5 million lines of Excel data per PMU per day.
Each line has voltage angle, freq, Vrms, modal information, …
Page 8 of 44
The Good News and the Bad News, cont.
The bad news – how do you deal with all the data, process it, and find the nuggets?
So we become Synchrophasor Detectives – EVERY day has surprises and clues.
We look for events, and when we find something interesting, we post it on the Texas SynchrophasorNetwork web page.
Let’s now take a look at some lessons learned thus far.
Page 9 of 44
Lesson 0. Either Wind Affects the US Congress, or the US Congress Affects Wind
Page 10 of 44
Thur Fri
West Texas voltage phase angle swings nearly 100º and back with respect to U.T. Austin in about 24 hours
Wind generation and West Texas phase angle can go through large daily swings
McDonald Observatory Voltage Phase Angle with respect to U.T. AustinMarch 25, 26, 2010
-60
-40
-20
0
20
40
60
24 36 48 60 7236 Hours Beginning 12am, March 24, 2010
Deg
rees
Wind Generation in ERCOT - MWMarch 25, 26, 2010
0
1000
2000
3000
4000
5000
6000
24 36 48 60 72
MW
48
Lesson 1. Every Day has Synchrophasor Surprises
Page 11 of 44
Generator Trips and Frequency Rises?24 Seconds, Beginning Mon, April 11, 2011, 01:31:36 CDT
59.85
59.90
59.95
60.00
60.05
60.10
0.6 0.7 0.8 0.9 1.0Minutes
Freq
uenc
y
UT 120VHarris 69kVUT Pan Am 120V
24 Seconds, Beginning Mon, April 11, 2011, 01:31:36 CDT
-2
0
2
4
6
8
10
0.6 0.7 0.8 0.9 1.0Minutes
Volta
ge P
hase
Ang
le
Harris 69kVUT Pan Am 120V
From Kent Saahoff, ERCOT: Thunderstorms with high winds and lightning in north Texas tripped a double circuit 345 KV line at 1:32 that also took out two large units carrying about 800 MW. Another 200 MW unit tripped about a minute later. Preceding high frequency probably caused by loss of load due to distribution outages caused by the severe weather.
Inertial Droop
Ringdown Starts
Freq. Jumps Up?
South Texas Angle Rises
Page 12 of 44
Voltage Phase Angles Relative to U.T. Austin (One-Minute Averages, 1800 Readings in Each Minute)
-60
-40
-20
0
20
40
60
0 24 48 72 96 120 144 168 192 216 240 264 288 312 336 360 384 408
Hour Beginning 00:00 CST, Sunday, March 27, 2011
McDUTPA
Voltage Phase Angles, 1-Minute Averages
-20
-10
0
10
20
30
40
50
24 Hours Beginning 18:00 CST, Saturday, April 2, 2011
McDUTPA
Zoom-In, 24 hours wide
1 2
2 2
1. Rapid wind gen ramp, approx 45º in 1.5 hours.
2. Unusual large, slow angle rings I had not noticed before. Period = 30 mins, 10º to 15º peak-to-peak.
Page 13 of 44
Frequency, 1-Minute Averages
59.90
59.95
60.00
60.05
60.10
8 Hours Beginning 10:00 CST, Sunday, April 3, 2011
McDUTPA
-20
-10
0
10
20
30
40
8 Hours Beginning 10:00 CST, Sunday, April 3, 2011
McDUTPA
Voltage Phase Angle, 1-Minute Averages
• Frequency measurements (bottom graph) are of course very valuable, but are basically the same across the grid
• Frequency variations are in the 3rd or 4th significant digit, near the limit of measurement resolution
• Phase angle measurements (top graph) are rich with regional response, providing “stereo vision” that is useful in localizing disturbances.
• Measured angle variations are much greater than the 0.1 degree accuracy.
Texas Nodal Market Has Created a New West Texas Resonant Mode with Time Period = 30 minutes
Page 14 of 44
Voltage Phase Angles, 1-Minute Averages
-20
-10
0
10
20
30
40
50
6 Hours Beginning 12:00 CST, Saturday, April 9, 2011
McDUTPA
5pm CST4pm
Sat., April 9, 2011. McDonald Observatory PMU Drops Out.
Page 15 of 44
Last 10 Minutes of Vrms at McDonald Observatory
0.95
0.96
0.97
0.98
0.99
1.00
1.01
1.02
0 1 2 3 4 5 6 7 8 9 10
Minute
Nor
mal
ized
Vrm
s
Sat., April 9, 20114:35pm, CST 4:45pm, CST
Zoom-In of the Last 10 Minutes of Vrms
Page 16 of 44
Last 10 Minutes of Vrms at McDonald Observatory
0.95
0.96
0.97
0.98
0.99
1.00
1.01
1.02
0 1 2 3 4 5 6 7 8 9 10
Minute
Nor
mal
ized
Vrm
s
Sat., April 9, 20114:35pm, CST 4:45pm, CSTLast 10 Minutes of Vrms at McDonald Observatory
0.95
0.96
0.97
0.98
0.99
1.00
1.01
1.02
0 1 2 3 4 5 6 7 8 9 10
Minute
Nor
mal
ized
Vrm
s
Sat., April 9, 20114:35pm, CST 4:45pm, CST
12 Seconds Centered Around Minute 5.5
0.96
0.97
0.98
0.99
1.00
1.01
5.4 5.5 5.6
Minute
Nor
mal
ized
Vrm
s
Zoom-In of 12 Seconds of Vrms
Page 17 of 44
McDonald Vrms at Restart
0.98
0.99
1.00
1.01
0 1 2 3 4 5 6
Minute Into Restart
McDonald Restarted About 11pm Monday Night
Page 18 of 44
McDonald Observatory Voltage Phase Angle w.r.t U.T. Austin 120V and Harris 69kV
-14
-13
-12
-11
-10
1600 1700 1800 1900 2000 2100 2200
Sample (30 samples per second)
Deg
rees w.r.t U.T. Austin
w.r.t Harris 69kV
10 seconds
• The fixed net multiple of 30 degree phase shift between U.T. Austin 120V and Harris 69kV has been removed. The variable but steady 0.1 degree power flow phase shift through the substation transformer has also been removed.
• Can you see any significant difference between the waveform seen by the 120V wall outlet (in black) and the waveform seen by the 69kV, 3Φ grid monitor (in red)? (The correct answer is NO!)
Voltage Ringdown at McDonald Observatory Observed at the Following Two Locations in Austin: a 120V Wall Outlet on Campus, and the Harris 69kV Substation that Feeds the Campus
Lesson 2. 120V Wall Outlets Work for Synchrophasors
Page 19 of 44
Steady-State Voltage Angle Between ECE Building 120V Wall Outlet and 69kV Substation Monitor Varies with UT Generation and Load
Week of April 27, 2011
Voltage Phase Angle Relative to UT Austin1-Minute Averages, Beginning Sunday, April 17, 2011
-5
-4
-3
-2
-1
0
0 24 48 72 96 120 144 168
Hour of the Week
Deg
rees
Harris
Page 20 of 44
Bus 7WINDBus 7WIND
500 km
Local conventional Pload,conv − Pgen,conv
Pexport
Thevenin Impedance jXTH
Central ERCOT
Vangle = 0
Vangle = δ
Wind MW Backdown. July 15, 2010. Thevenin Impedance Calculation, cont.
Use the Excel Solver with the 90 minutes of readings tominimize least-squared error and determine Xth
Lesson 3. You Can Estimate Thevenin Equivalent Impedances Across the Grid with Synchrophasors
Page 21 of 44
West Texas Power Export Estimates Pexp1 and Pexp2, MW
-1000
0
1000
2000
3000
0 10 20 30 40 50 60 70 80 90
Minute Beginning 0400 CDT, July 15, 2010
90-Minute Window
Wind MW Backdown. July 15, 2010. Thevenin Impedance Calculation, cont.
Squared area between the two curves is minimized whenA = -0.0471
B = 356
Xth = 0.0211 pu on 345kV, 100MVA base
Page 22 of 44
2 Hz Cluster
March 18, 02:00 – 03:00 Wind Generation > 20%
March 12, 02:00 – 03:00 Wind Generation ≈ 2%
Big Wind (20%) with 2 Hz Cluster Small Wind (2%) without 2 Hz Cluster
Lesson 4. A 2 Hz Mode in Ambient Oscillation Sometimes Forms with High Wind Generation
Page 23 of 44
Start Sec Stop Sec A t1 B Tau1 t2 C Tau2 Wdamp 2010/10/04 18:18:00.015 30 -41.60 21.38 -45.65 0.19 21.37 4.28 1.95 3.82 PMUs = McDonald 1P
Fdamp Zeta Angle reference = Aus0.608 0.134
UT Pan Am Voltage Angle with respect to U.T. Austin, 2010/10/04 18:18:00.000
-49
-48
-47
-46
-45
-44
-43
-42
-41
-40
15 20 25 30 35
MeasuredCurve Fit
Healthy response to a unit trip
Lesson 5. Wind Generation Does Not Appear to Impact System Damping or Damped Resonant Frequency
Page 24 of 44
Ringing Frequency vs Wind Generation (% of Total), Sep 2009 ‐ Feb 2010
0
0.5
1
1.5
2
2.5
3
0 2 4 6 8 10 12 14 16 18 20
Wind Generation (% of Total)
Freq
uency (Hz)
Ringdown Analysis of More Than 100 Unit Trips Yields No Clear Relationship Between Wind MW and Damped Resonant Frequency
Does Wind Generation Impact Grid Stability?
Page 25 of 44
Damping Ratio vs Wind Generation (% of Total), Sep 2009 ‐ Feb 2010
0
0.2
0.4
0.6
0.8
1
1.2
0 2 4 6 8 10 12 14 16 18 20
Wind Generation (% of Total)
Normalized
Dam
ping
Ratio
Ringdown Analysis of More Than 100 Unit Trips Yields No Clear Relationship Between Wind MW and Normalized Damping Ratio
Does Wind Generation Impact Grid Stability?
Page 26 of 44
( )rated
s
s
m
rated
ss
rated
s
PdtdP
PJ
P
JH ω
ωωωω
⎥⎦
⎤⎢⎣
⎡ Δ−=
•=≡
/21
212
1 2
( ) ( ) ( )dtdfPfP
dtdff
PP
dtdPPH
srated
sm
s
s
rated
m
s
s
rated
m/2/2
22/2
1 Δ−=
Δ−=⎥
⎦
⎤⎢⎣
⎡ Δ−=
ππ
ωω
H has the units of seconds. The correct interpretation is that the kinetic energy in the equivalent system machine corresponds to H seconds of rated power. Thus, the machine could provide rated power for H seconds, at which time it would have spun down to zero RPM.
EPRI Study. Purpose – to compute ERCOT System Inertia Constant H From Frequency Response During 42 Unit Trips Having 0.1 Hz or Greater Freq. Drop.
Lesson 6. Wind Generation Does Not Appear to Reduce System Inertia(but no generator operating at max power can contribute to governor
response)
Page 27 of 44
August 2010, Event 7, cont.
Event 7Voltage Phase Angle Event 7, 8/24/2010 07:31:00 PM GMT Minute
59.82
59.84
59.86
59.88
59.90
59.92
59.94
59.96
59.98
60.00
56 57 58 59 60 61 62 63 64 65 66
Second of the Minute
Freq
uenc
y UT AustinHarris 69McDUT PanAm
Inertia slope
Nadir slope
Zoom
Page 28 of 44
Estimated System H versus % Wind Generation(42 Unit Trip Events, June through November 2010)
0
2
4
6
8
10
12
0 5 10 15 20
Wind Generation - % of Total Generation
Estim
ated
H42 Major Unit Trips, 0.1 Hz or Greater. Any Correlation Between System
Inertia and Wind Generation (% of Total Gen)?
Page 29 of 44
Estimated System H versus Wind Generation (MW)(42 Unit Trip Events, June through November 2010)
0
2
4
6
8
10
12
0 1000 2000 3000 4000 5000 6000 7000
Wind Generation - MW
Estim
ated
H42 Major Unit Trips, 0.1 Hz or Greater. Any Correlation Between System
Inertia and Wind Generation (MW)?
Page 30 of 44
Event 7, 8/24/2010 07:31:00 PM GMT Minute
59.82
59.84
59.86
59.88
59.90
59.92
59.94
59.96
59.98
60.00
56 57 58 59 60 61 62 63 64 65 66
Second of the Minute
Freq
uenc
y UT AustinHarris 69McDUT PanAm
Inertia slope
Nadir slope
ΔTnadir
ΔFnadir
ΔFinertia
August 2010, Event 6, 8/24/2010, 07:31:00 PM GMT
Figure 48. Introduction and Graphical Illustration of the Proposed New Metric, Frequency Recovery Ratio (FFR).
FrequencyRecoveryRatio
nadir
inertiaFF
FRRΔΔ
≡
Page 31 of 44
• 42 Major Unit Trips, 0.1 Hz or Greater. FRR is affected by wind generation because wind generators typically operate at max power and thus have no spinning reserve.
• But wind generators do not appear to reduce system inertia.
Frequency Recovery Ratio (FRR) versus % Wind Generation(42 Unit Trip Events, June through November 2010)
0
1
2
3
4
0 5 10 15 20Wind Generation - % of Total Generation
FRR
Page 32 of 44
Let’s Do Some Detective Work for This Week
Voltage Phase Angle Relative to UT Austin1-Minute Averages, Beginning Sunday, April 24, 2011
-50-40-30-20-10
01020304050
0 24 48 72 96 120 144 168
Hour of the Week, CDT
Deg
rees McD
PanAm
Sun Mon Tue
Page 33 of 44
Voltage Phase Angle Relative to UT Austin1-Minute Averages, Monday, April 25, 2011, Beginning 09:00 CDT
-20
-10
0
10
20
30
40
33 36 39 42 45
Hour of the Week, CDT
Deg
rees McD
PanAm
Looks Like the New Texas Nodal Market Oscillation ProblemIs Still Here
Page 34 of 44
Angle Ringdownat McD
1 Minute Window Angle Ringdown at PanAm
1 Minute Window
Page 35 of 44
59.98
59.99
60.00
60.01
60.02
60.03
60.04
60.05
0 1 2 3
Minutes
Hz Harris 69
PanAm
Frequency, 3 Minutes Beginning April 24, 2011,19:54 CDT
59.98
59.99
60.00
60.01
60.02
60.03
60.04
60.05
0 1 2 3
Hz Harris 69
McD
Page 36 of 44
Voltage Phase Angle, 3 Minutes Beginning April 24, 2011,19:54 CDT
-1
0
1
2
3
0 1 2 3
Deg
rees
McD
18
19
20
21
22
0 1 2 3
Minutes
Deg
rees
PanAm
Page 37 of 44
Unit Trip,
April 24, 2011,
21:15 CDT
Page 38 of 44
Unit Trip,
April 24, 2011,
21:15 CDT
Page 39 of 44
PanAm
McD
Unit Trip, April 24, 2011, 21:15 CDT
Page 40 of 44
Start Sec Stop Sec A t1 B Tau1 t2 C Tau2 Wdamp24.5 28.9 13.31 24.88 13.98 0.14 25.14 0.88 2.97 3.68
Fdamp Zeta0.585 0.092
Unit Trip April 24, 2011, 21:15:25 CDT. McDonald Angle Relative to U.T. Austin
13
14
15
23 24 25 26 27 28 29 30 31 32 33Seconds
Deg
rees
MeasuredCurve Fit
Damped Resonant Frequency, Hz Normalized
Damping Coefficient
Ring Magnitude, degrees
Steady-State Change = 13.98 – 13.31 = 0.7 degrees
McDonald
Page 41 of 44
Start Sec Stop Sec A t1 B Tau1 t2 C Tau2 Wdamp24.5 28.9 17.68 24.62 14.40 0.23 24.93 -2.23 1.58 3.71
Fdamp Zeta0.591 0.170
Unit Trip April 24, 2011, 21:15:25 CDT. Pan Am Angle Relative to U.T. Austin
12
13
14
15
16
17
18
23 24 25 26 27 28 29 30 31 32 33Seconds
Deg
rees
MeasuredCurve Fit
Damped Resonant Frequency, Hz Normalized
Damping Coefficient
Ring Magnitude, degrees
Steady-State Change = 14.40 – 17.68 = -3.3 degrees
Pan Am
Page 42 of 44
Damped Oscillation Frequencies, Magnitudes, and Normalized Damping Ratiosfor the Hour 21:00 – 22:00 CDT, April 24, 2011
McD Voltage Angle Relative to UT Austin UT Pan Am Voltage Angle Relative to UT Austin
Page 43 of 44
Texas Synchrophasor Network
Thanks to
• Schweitzer Engineering Laboratories, especially Mr. David Costello, for providing all the equipment and technical support that we need
• EPRI, especially Ms. Karen Forsten and Mr. Daniel Brooks, for past, present, and future funding of graduate students and faculty summer support
• Startup money in 2008 from the Texas Governor Rick Perry’s Emerging Technology Fund through CCET, Dr. Milton Holloway
• Austin Energy, especially Mr. Scott Bayer, for installing the 69kV phasor measurement unit, and providing advice on system operating and protection
• PhD student Moses Kai at U.T. Austin for his dedication and research in synchrophasors and their applications to power grids
Page 44 of 44