IEEE Power & Energy Magazine - September/October 2015 - 40

60.040
60.035
60.030
60.025
60.020
60.015
60.010
60.005
60.000
59.995
59.990
59.985
59.980
59.975
59.970

Hz

Frequency

Start of
Oscillations

6:14 p.m.

figure 3. The start of oscillations.

Reduction in
Power Output
at 10:54 a.m.

60.045
60.040
60.035
60.030
60.025
60.020
60.015
60.010
60.005
60.000
59.995
59.990
59.985

Hz

Frequency

Damping %
Less than 1%

0.03
0.03
0.02
0.02
0.01
0.01
0.00

Damping (%)

3.34
3.34
3.34
3.3 Hz
3.34
3.33
3.33
3.33
Constant Frequency Indicates
Presence of a Single Mode of Oscillation 3.33
3.33
3.32
Oscillation Frequency

Mode Frequency
(Hz)

figure 4. The end of oscillations after the 40-MW
constraint.

figure 5. Oscillation frequency and damping.

21 networked PMUs installed at seven 345-kV substations.
LCRA TSC is in the early phase of integrating PMU data
into control center operations. Real-time visualization and
alarming is monitored by operations engineers with voltage
transient, angle difference transient, frequency transient, and
oscillatory events captured for postevent analysis. Captured
events are reviewed to increase understanding of dynamic
events that occur on the system. Small signal stability and
voltage sensitivity are validated through the assessment of
historical alarms.
In the future, LCRA TSC will make PMU data available to system operators. Wind generators are known to
be susceptible to oscillations, produce reactive power
when not generating, and occasionally inject large harmonic currents affecting system voltage. PMU data will
be used to perform analysis that will raise alarms in the
control center, allowing an operator to immediately identify the specific resource causing voltage or oscillatory

40

ieee power & energy magazine

issues. The operator will know which generator to contact and potentially disconnect, if necessary, to maintain
system reliability. The LCRA TSC planning and ERCOT
operations groups will be notified in this process.
In addition to preventing system issues caused by renewable resources, locations that have operable reactive devices
and are near wind generation in West Texas will be monitored for voltage sensitivity. Alarms will be used to make the
operator aware of the need to adjust reactive support based
on real-time voltage stability.
Further down the road, LCRA TSC will install PMUs
for use in black start. Visualization from strategically
placed PMUs will help operators monitor the system for
stability when it is most vulnerable. Feedback from frequency, voltage, and angle monitoring will indicate which
actions increase or decrease system stability and strength
as the operator is building back LCRA TSC's system and
synchronizing with other TOs. The feedback will help the
operator verify that his actions are moving the system in a
better direction and allow him to reverse course if system
performance worsens during restoration.

For Further Reading
NERC. (2010, Oct.). Real-time applications of synchrophasors for improving reliability. [Online]. Available: https://
www.naspi.org/File.aspx?fileID=519
NASPI. List of actual and potential phasor data applications. (2009, Dec. 1). [Online]. Available: https://www.naspi.
org/File.aspx?fileID=537 >
CCET, (2014, Apr.) Technology solutions for wind integration in ERCOT. [Online]. Available: www.electrictechnologycenter.com/pdf/TPR2Rev0Chg0043014.pdf
J. Chen, P. Shrestha, S.-H. Huang, N. D. R Sarma, J. Adams, D. Obadina, and J. Ballance, "Use of synchronized phasor measurements for dynamic stability monitoring and model
validation in ERCOT," in Proc. IEEE PES General Meeting,
San Diego, CA, July 2012, pp. 1-7.
S. Rajagopalan, S. Nuthalapati, T. Mortensen, and
B. Blevins, "Post-event analysis of a compound event in the
ERCOT system using synchrophasor data," in Proc. CIGRE
Grid of the Future Symp. Houston, TX, 2014, pp. 1-9.

Biographies
Kristian M. Koellner is with the Lower Colorado River Authority, Austin, Texas.
Spencer Burks is with the Lower Colorado River Authority, Austin, Texas.
Bill Blevins is with ERCOT, Austin, Texas.
Sarma (NDR) Nuthalapati is with ERCOT, Austin,
Texas.
Sidharth Rajagopalan is with ERCOT, Austin, Texas.
Milton L. Holloway is with the Center for Commercialization of Electric Technology, Austin, Texas.
p&e

september/october 2015


http://https:// http://www.naspi.org/File.aspx?fileID=519 https://www.naspi http://www.electrictech http://www.nologycenter.com/pdf/TPR2Rev0Chg0043014.pdf

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