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 Hz o 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 • 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

1. Forced Oscillation Event Analysis
January 11, 2019 Event
Ryan D. Quint, PhD, PE
Senior Manager, Advanced System Analytics and Modeling, NERC
February 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 Hz
o 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
• 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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Observations
FPL

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Observations
FPL

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Observations
FPL

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Observations
FPL

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Observations
TVA
Event
200 MW
Peak to peak
SCADA Data – Flow on 500 kV tie line with
Southern Company (Bradley-Conasauga)

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Observations
TVA

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

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Observations
ATC

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Observations
ComEd
Current on an east-west 765kV line

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Observations
AEP
03:45:00 03:50:00 03:55:00 04:00:00
Time (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
FFTMagnitude

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Observations
Duke 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.
Observations
ISO-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.
Observations
WSU

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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.
Observations
WSU

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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.
Observations
WSU

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Observations
WSU

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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, PE
Senior Manager
Advanced System Analytics and Modeling
North American Electric Reliability Corporation
Office (202) 400-3015
Cell (202) 809-3079
ryan.quint@nerc.net