Forced Oscillation Event AnalysisJanuary 11, 2019 Event

Ryan D. Quint, PhD, PESenior Manager, Advanced System Analytics and Modeling, NERCFebruary 2019

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• Oscillation observed across entire Eastern Interconnection from 08:44:41 UTC (03:44:41 EDT) to 09:02:23 UTC (04:02:23 EDT) Oscillation frequency of 0.25 Hzo Aligns with inter-area mode frequency across EI

Power swings around Florida of 200 MW, around ISO-NE of 50 MW

• RCs identified oscillation on PMU data, notified RC Hotline• UTK provided videos of oscillation event• GOs noticed oscillation on power plants across EI• Source tentatively determined as Bayside #2 Steam Unit• NERC issued PMU data request, working with possible source• NERC will perform oscillation analysis on wide-area data set• NERC working with industry to study event, develop mitigating

actions

Background

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NERC PI System

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• Strange oscillation in Florida around 08:44:21 UTC (03:44:21 EDT)

Overview of Oscillation

• Oscillation strengthens at 08:44:41 UTC (03:44:41 EDT)

• Oscillation ends at 09:02:23 UTC (04:02:23 EDT)

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• Video of onset of oscillation: https://www.youtube.com/channel/UC40n2KTjwRhC9_CvtIasaWA/videos https://www.youtube.com/watch?v=xilfYKxqEDo https://www.youtube.com/watch?v=VDsKAe9p9f0 https://www.youtube.com/watch?v=pnSRKI9sLWY https://www.youtube.com/watch?v=j0I2ezmlRXM https://www.youtube.com/watch?v=Zfc-UcEn3Fw https://www.youtube.com/watch?v=doPgbh8PedQ https://www.youtube.com/watch?v=E9_5DPx85bc

FNET Videos

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FNET Information

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Generator Analysis

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ObservationsFPL

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ObservationsFPL

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ObservationsFPL

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ObservationsFPL

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ObservationsTVA

Event

200 MW Peak to peak

SCADA Data – Flow on 500 kV tie line with Southern Company (Bradley-Conasauga)

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ObservationsTVA

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ObservationsATC

• Plot is sum of 5 EHV lines connecting from Wisconsin to Illinois

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ObservationsATC

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ObservationsComEd

Current on an east-west 765kV line

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ObservationsAEP

03:45:00 03:50:00 03:55:00 04:00:00Time (Eastern)

-200

0

200

MW

Antioch at JacksonsFerry

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5

Frequency (Hz)

0

20

40

60

80

FFT

Mag

nitu

de

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ObservationsDuke Energy

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• ISO-NE Phasorpoint generated 14 alarms (20+ Alerts) from 3:46-4:03 AM, 0.249 Hz oscillation, magnitudes up to 10-15 MW RMS

• OSL application automatically processed Alarms and Alerts, identified source of oscillations located beyond ISO-NE area

• Plot: MW flow on 345KV line between NE and NY.

ObservationsISO-NE

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• NERC issued data request at 9:05 PM EDT on 1-11-2019 to gather PMU data from RCs

PMU Data Collection

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• FFDD TVA-only data analyzed Damping of estimated mode with frequency 0.25 Hz is close to zero. Well-damped mode before and after event with frequency of 0.24Hz. Appears that well-damped mode is the well-known 0.22 Hz North-South

mode of EI Conclusion that event caused by forced oscillation with frequency close to

system mode. Analysis of data with FSSI engine in the next section will make the analysis

clearer. Oscillatory modes of 0.75 Hz and 1 Hz dominant estimated modes before

and after event. Both modes show low damping, may be related to other forced oscillations. Further analysis of these modes requires more PMU data.

ObservationsWSU

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• FSSI: TVA-only data analyzed Once event starts, mode with frequency of 0.25 Hz with damping about

zero percent is clear in time plots. Analysis of voltage phase angles and current phase angles shows that

during event there are two estimates with close frequencies about 0.25Hz.o One of these estimates, which seems to be the system mode with frequency

about 0.23Hz, is a well-damped mode. This mode is persistent before, during, and after the event.

o Another estimation with the frequency of 0.25 Hz appears during the event with damping about zero. The oscillation seems to be a forced oscillation which is happening at the frequency close to the system mode frequency.

Since frequency of forced oscillation and system mode is very close, there is strong evidence that this event was related to inter-area resonance effect between system mode and forced oscillation.

ObservationsWSU

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• WSU Conclusions: Online tool detected 0.25 Hz oscillation with high energy, ~0% damping. All 3 engines FFDD, FSSI, and EAO detect and alarm the low-damping

oscillations with frequency of 0.25 Hz once the event starts. Before and after event, system mode with f = 0.23-0.25 Hz well-damped. Analysis of phase angle data by FSSI showing two persistent modes with

close frequencies of about 0.25 Hz. o Well-damped mode seems to be the system mode and the one with damping

near zero seems to be a forced oscillation. o More detailed studies with additional PMU data is needed to determine the

effect of possible inter-area resonance phenomenon. Before and after the event, poorly damped 0.75Hz mode is likely caused by

the well-known forced oscillation in EI that has been present for years. Phase angle signals (both voltages and currents) are showing a very low-

damping mode with frequency of 1 Hz which may be related to clock issues in some of the PMUs. These should be fixed.

ObservationsWSU

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ObservationsWSU

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• Repowered combined cycle plant – steam turbine oscillating• Power-load imbalance (PLI) controls• Failed potential input feeding feedback Feedback reading 2/3 power output vs. input – perceived imbalance

• Drives shut intercept valves• 4 second timer to reopen valves – open/close cycle• Different potential inputs for relaying and controls/metering Relaying hence did not pick up the imbalance/issue

• Plant manually tripped by operator• Upon inspection, failed wiring in PT cabinet• Damaged intercept valves, needed replacement, unit off-line for

relatively extended period (couple weeks)

Source Oscillation

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Overview of Forced Oscillation

Errored Signal

Forcing Function

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Ryan Quint, PhD, PESenior ManagerAdvanced System Analytics and ModelingNorth American Electric Reliability CorporationOffice (202) 400-3015Cell (202) 809-3079ryan.quint@nerc.net