jsis march 4, 2015 wide-area damping monitoring using pmu data joe h. chow, felipe wilches-bernal...

JSISMarch 4, 2015

Wide-Area Damping Monitoring using PMU Data

Joe H. Chow, Felipe Wilches-BernalRensselaer Polytechnic Institute

X. Tony JiangQuanta Technology

Dmitry KosterevBPA

WECC JSIS March 2015 JHC 2

Damping assessment using relative phase information from PMU data

• Power systems with long transmission lines for power transfer tend to have lightly damping interarea modes, e.g., Western US power system (WECC), Nordel power grid

• The interarea mode damping is achieved by application of power system stabilizers (PSSs) on multiple generators.

• Unfortunately, some of these PSSs may be poorly tuned because the interarea mode shapes have changed.

• As a result, WECC wants to develop model identification techniques for generators, excitation systems, and PSSs, so that the damping contribution to the interarea modes can be properly assessed.

• However, generator testing requires taking it off-line, which can be costly


Damping assessment using relative phase information from PMU data

• Is it possible to assess the damping contribution of a particular generator (with its PSS) by measuring disturbance response?

• This question is not addressed in control system theory for large-scale systems

• We have recently developed a technique using linearized power system models to assess such damping contributions

• The method looks at the phase differences between the generator rotor angle (or speed) and its terminal bus angle (or frequency)

• The method can be applied to disturbance simulation or PMU data (requiring methods such as Prony, Eigensystem Realization Algorithm, or N4SID to extract the modal components)


Linearized Model Block Diagram of a Single-Machine infinite-Bus System

Heffron and Phillipsde Mello and Concordia


Synchronizing and Damping Torque Decomposition - SMIB


Interarea Mode Damping Result

• For each generator, find the phase difference between the interarea mode content of the terminal bus voltage angle and the generator angle, for example, for generator 1:

• If this difference is • Positive and large, then PSS contributes good damping• Negative, then this machine is contributing negative damping torque • Positive but small – need to look at the setting of the PSS

• The damping for each generator is assessed using its own measurements

• To apply the method in real time – after any disturbance resulting in sustained interarea mode oscillation, use the PMU data to check this phase difference for all critical generators. Note that the rotor angle can be measured with a regular digital recording device.

1 1m m


Alstom/Psymetrics Results

• N. Al-Ashwal, D. Wilson, and M. Parashar, “Identifying sources of oscillations using wide area measurements,” 2014 Grid of the Future Symposium, CIGRE US National Committee, 2014.

• Their method uses the rotor angle mode shapes to find the relative phase between different generators and use the information to determine damping contribution


DK WECC Simulation

• Earlier Hongming Zhang asked Brian Thomas of GE to perform some WECC simulations for RPI. The scenarios selected did not show significant oscillations. Thus our method could not be used. Presented at the 10/2014 JSIS.

• Then Dmitry provided a scenario with significant oscillations• 2 cases for the scenario:

• No PSS’s • A few PSS’s turned on

• RPI was provided with the time response of a selected set of generators (rotor angle, rotor speed, generator terminal bus angle, generator terminal bus frequency).

• RPI was not told which generators had the PSS turned on. The intent is to use the modal angle difference to find those generators with their PSS’s turned on.


Case 1: All PSS’s off

0 5 10 15 20 25 30 35

0

0.1

0.2

0.3

Case1 OFF

Time(sec)

Bus

angle(rad)

G1G2G3G4G5G6G7G8G9G10

0 5 10 15 20 25 30 35

-0.2

-0.1

0

0.1

0.2

0.3

0.4Case1 OFF

Time (sec)

Rotorangle(rad)


0 5 10 15 20 25 30 3559.9

60

60.1

60.2

60.3

60.4

Case1 OFF

Time(sec)

Bus

Freq(Hz)


0 10 20 30

0.998

1

1.002

1.004

1.006

1.008

Case1 OFF

Time (sec)

RotorSpeed(pu)



Case 1: A Few PSS’s On

0 5 10 15 20 25 30 350

0.1

0.2

0.3

Case1 ON

Time(sec)

Bus

angle(rad)


0 5 10 15 20 25 30 35

-0.2

-0.1

0

0.1

0.2

0.3

0.4Case1 ON

Time (sec)

Rotorangle(rad)


0 5 10 15 20 25 30 35

60

60.1

60.2

60.3

60.4

Case1 ON

Time(sec)

Bus

Freq(Hz)


0 10 20 300.998

1

1.002

1.004

1.006

1.008Case1 ON

Time (sec)

RotorSpeed(pu)



Case 1: All PSS’s Off – Gen 1

blue: term. bus angle, green: rotor angle blue: term. bus frequency, green: rotor speed

-5 0 5 10 15 20 25 30 35 400.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

-5 0 5 10 15 20 25 30 35 400.995

1

1.005

1.01


DK Case Analysis

• All generators in one coherent group, so they all have similar swings

• The bus angles and rotor angles are plotted against an average angle. Modal information was difficult to extract from the angles (depending on the reference angle) – Brian has resolved this issue.

• Instead, use an alternative approach of calculating the relative phase difference

associated with the interarea mode.


DK Case Results

• For each generator, compute the relative phase change between no PSS on to some PSS’s on.

• Machines with large phase increases have effective PSS’s Generato

r Angle diff change (deg) PSS

1 3.03 N

2 12.09 Y

3 11.21 Y

4 1.79 N

5 1.11 N

6 5.00 N

7 5.24 N

8 -0.03 N

9 12.29 Y

10 -6.80 N


Next Steps

• Partial results submitted to 2015 Power Tech Conference

• Resolve some of the outstanding issues in modal information extraction

• Testing of the method on a few generators in a real power system (like WECC) • PMU monitoring of generator terminal buses• Generator rotor speed and angle measurements

with GPS signal and synchronized to PMU sampling

• 30 or 60 samples per second?

This work was supported primarily by the ERC Program of the National Science Foundation and DOE under NSF Award Number EEC-1041877.

Other US government and industrial sponsors of CURENT research are also gratefully acknowledged.

Other industry/agency collaborators: NYPA, NYSERDA, Hitachi, Grid Protection Alliance, BPA, SCE, GCEP

Acknowledgements

jsis march 4, 2015 wide-area damping monitoring using pmu data joe h. chow, felipe wilches-bernal...

Documents

wecc jsis

damping contribution

damping assessment

damping contributions

interarea mode damping

generator angle

wecc simulations

good damping negative