1. Lessons Learned from the Texas 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

2. Austin 120V and Harris 69kV Waco Houston (SEL) Boerne (SEL) The Texas Synchrophasor Network Six 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

3. 48 ThurFri 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

4. Texas Nodal Market Has Created a New West Texas Resonant Mode with Time Period = 30 minutes 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.

5. 3600 points McD Angle McD, PanAm, Waco Frequencies Transmission Events Also Produce Angle Rings 2011/06/03, 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 (2 nd significant digit) Frequency ring is only about 0.01 Hz peak to peak (4 th significant digit) Lesson 1. Daily surprises, cont. 5 2 minutes 5 minutes 2 minutes

6. 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

7. 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

8. 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

9. 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

10. 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

11. Lesson 5. Wind does not impact damping, cont. 11 10 seconds Let Excel Solver Curve Fit the 2 nd Order Damped Response Damped Resonant Frequency, Hz Ring Magnitude, degrees Steady-State Change = 18.58 – 17.05 = 1.53 degrees Normalized Damping Ratio

12. 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? Lesson 5. Wind does not impact damping, cont. 12 6 months

13. 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

14. 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

15. 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