lessons learned from the texas synchrophasor network by presented at the
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Lessons Learned from theTexas Synchrophasor Network
by
Presented at the
North American Synchrophasor Initiative (NASPI) Meeting
Toronto, Ontario
Thursday, June 9, 2011
W. Mack Grady and Moses Kai, U.T. Austin
Bill Flerchinger and David Costello, Schweitzer Engineering Labs
Karen Forsten and Daniel Brooks, EPRI
1
UT Pan Am
Austin
McDonald Observatory Austin 120V and
Harris 69kV
Waco
Houston (SEL)
Boerne (SEL)
The Texas Synchrophasor NetworkSix 120V single-phase PMUs, One 69kV three-phase PMU
Brazos Electric PMU
Austin Energy PMU
• Funding provided by EPRI
• Equipment provided by Schweitzer Engineering Labs
Wind country
Concentrated distant load
Blue outlines: Central ERCOT
2
McDonald Observatory
UT Pan Am
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 72
36 Hours Beginning 12am, March 24, 2010
De
gre
es
Wind Generation in ERCOT - MWMarch 25, 26, 2010
0
1000
2000
3000
4000
5000
6000
24 36 48 60 72
MW
48
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
Lesson 1. Every Day has Synchrophasor Surprises
3
2 days
Texas Nodal Market Has Created a New West Texas Resonant Mode with Time Period = 30 minutes
McDonald Observatory Voltage Phase Angle Relative to Central ERCOT
-20
-10
0
10
20
30
40
0 1 2 3 4 5 6 7 8 9 10 11 12
Hour of March 11, 2011
De
gre
es
ERCOT’s graph of West-to-North P flow
Texas Synchrophasor Network’s graph of West-to-Central ERCOT Voltage Angle
4
12 hours
Lesson 1. Daily surprises, cont.
3600 points
McD Angle
McD, PanAm, Waco Frequencies
Transmission Events Also Produce Angle Rings2011/06/03, 00:54 GMT
59.94 Hz
60.02 Hz
Frequency Slump
• The angle ring observed at McD and Waco was likely caused by a transmission event and was a precursor to a gradual frequency slump.
• Angle ring is approx. 1 degree peak to peak (2nd significant digit)
• Frequency ring is only about 0.01 Hz peak to peak (4th significant digit)
Lesson 1. Daily surprises, cont. 5
2 minutes
5 minutes
2 minutes
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)
De
gre
es
w.r.t U.T. Austin
w.r.t Harris 69kV
10 seconds
20 seconds
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
• The fixed net multiple of 30 degree phase shift between U.T. Austin 120V and Harris 69kV has been removed. The variable but steady power flow phase shift through the substation transformer has also been removed.
Lesson 2. 120V Wall Outlets Work for Synchrophasors (of course, we would prefer to have three-phase grid PMUs)
6
-1
0
1
0 24 48 72 96 120 144 168
Hour of the Week, CDT
De
gre
es
Harris
Steady-State Voltage Angle Between Austin Energy 69kV Substation Monitor and UT ECE Building 120V Wall Outlet Varies Slowly with UT Generation and Load
Week Starting Sunday, May 29, 2011
Lesson 2. 120V OK, cont. 7
1 week
Note – angles shown were rounded to 0.1º
Bus 7WINDBus 7WIND
500 km
Local conventional Pload,conv − Pgen,conv
Pexport
Thevenin Impedance jXTH
Central ERCOT
Vangle = 0
Vangle = δ
Use the Excel Solver with angle measurements to minimize least-squared error and obtain Xth
Lesson 3. You Can Estimate Thevenin Equivalent Impedances Across the Grid with Synchrophasors
8
McDonald Observatory Voltage Phase Angle Relative to Central ERCOT
-20
-10
0
10
20
30
40
0 1 2 3 4 5 6 7 8 9 10 11 12
)sin(21 THX
VVP
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 ClusterSmall Wind (2%) without 2 Hz Cluster
Lesson 4. A Small but Tightly-Clustered 2 Hz Mode in Ambient Oscillation Sometimes Forms with High Wind Generation
9
1 hour
Lesson 5. Wind Generation Does Not Appear to Impact System Damping or Damped Resonant Frequency
McD
PanAm
Waco
10
5 minutes of frequencies
1 minute of angles
59.74
Modest wind
Lesson 5. Wind does not impact damping, cont. 11
Unit Trip 2011/05/30 03:03:00 GMT. UT Pan Am Relative to U.T. Austin.
16
17
18
19
20
21
5 6 7 8 9 10 11 12 13 14 15
Second
De
gre
es
Measured Total Curve Fit
10 seconds
)()(sin)( 222
)2(
11
)1(
TtuTteCTtueBAB d
TtTt
Let Excel Solver Curve Fit the 2nd Order Damped ResponseAvg. Sum
Start Sec Stop Sec A B T1 Tau1 C T2 Tau2 Tdamp Fdamp Zeta Squared Error5.5 11 17.05 18.58 5.91 0.24 1.73 6.18 4.64 1.59 0.628 0.055 0.0044
Alpha0.215
F00.629
Exponential Steady State Transition Curve Damped Sinusoidal Term
Damped Resonant Frequency, HzRing Magnitude, degrees
Steady-State Change = 18.58 – 17.05 = 1.53
degreesNormalized
Damping Ratio
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)
Nor
mal
ized
Dam
ping
Rati
oRingdown Analysis of More Than 100 Unit Trips Yields No Clear Relationship
Between Wind MW and Normalized Damping Ratio
Does Wind Generation Impact Grid Stability?
Lesson 5. Wind does not impact damping, cont. 12
6 months
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
Fre
qu
ency
UT Austin
Harris 69
McD
UT PanAm
Inertia slope
Nadir slope
Zoom
Lesson 6. Wind Generation Does Not Appear to Reduce System Inertia(but no generator operating at max power can contribute to governor
response)
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.
13
10 seconds
2 minutes
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
Est
imat
ed H
42 Major Unit Trips, 0.1 Hz or Greater. Any Correlation Between System Inertia and Wind Generation (% of Total Gen)?
Lesson 6. Wind does not reduce system inertia, cont. 14
6 months
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
• Mr. Andrew Mattei of Brazos Electric, Waco, for installing and operating a 120V PMU
• PhD student Moses Kai at U.T. Austin for his dedication and research in synchrophasors and their applications to power grids
15
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