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

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