1

Mani V. Venkatasubramanian Washington State University

Oscillation Monitoring

of Large-Scale

Power Systems

© Washington State University

Stability Requirements

• Voltage Stability

– Sufficient reactive power reserves?

– Voltage collapse

• Small-Signal Stability

– Can damp out small disturbances?

– Oscillatory instability

• Transient Stability

– Can withstand large disturbances?

– Loss of synchronism and islanding

• Operational Reliability

© Washington State University

2

3

Real-time security monitors @ WSU

Oscillation

Monitoring

System

Voltage

Stability

Monitor

Angle

Stability

Monitor

PMU

Real-time

data

PMUs

&

PDC

System

Security

Status

Real-time

Display &

Control

Entergy, IPC

Entergy, IPC

Small-Signal Stability

Negative damping

Growing oscillations

Positive damping

Oscillations damp out

1

2

4 3

1 2

3 4

© Washington State University

4

Small-signal Stability

Well-damped Poorly damped

time

Position

time

Position

© Washington State University

5

Small-Signal Stability Issues

• Poorly damped oscillations

– Causes rotor fatigue

– Rotor life-span shortened

– Power quality issues

• Sustained oscillations

– Coupled oscillations and forced oscillations

– Rotor fatigue

– Can lead to tripping of generators

• Growing oscillations

– Can lead to tripping of generators and lines

– May lead to cascading blackouts

© Washington State University

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© Washington State University

7

Small-signal Instability in WECC

Northwest

California

COI

lines

August 10, 1996 WECC blackout

Negative damping

Growing oscillations Unstable 0.25 Hz

Inter-area mode

300 350 400 450 500 550 600 650 700 750 800

1100

1200

1300

1400

1500

1600

1700

Time (s)

M

W

Malin to Round_Mountain 1_Line MW flow vs time

Keeler-Allston line trips

Ross-Lexington line trips

© Washington State University

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8

Small-Signal Local Event

Plant

System

1.2 Hz local mode

Negative damping:

Growing

oscillations

Positive

damping:

Oscillations

damp out

Oscillation Monitoring System

OpenPDC

OMS

OMS action adapters built into OpenPDC 64 bit version 2.

IEEE C37.118

BPA PDCstream

Real-time PMU

data stream OMS results

OMS

openPDC

SQL server

Open PDC

historian

Architecture

OMS

openPDC

PMU 1

PMU 2

PMU 3

PMU 4

PMU 5

PMU N OMS custom action adapters built into openPDC version 2.

Historian

SQL Database

Published

Results from Two Engines

820 840 860 880 900 920 940

5.09

5.1

5.11

5.12

5.13

5.14

5.15

x 105

Time (s)

Vol

tage

(V)

Bus Voltage Magnitude at Cumberland

Event Analysis

1.2 Hz at +1.5% damping. Local Mode.

Ambient Noise Analysis

1.2 Hz at +1.8% damping. Local Mode.

Nov. 29th 2007 TVA event

FDD

analysis for

ambient data

Event?

Prony analysis

for post-

disturbance data

Start

Read data

from PDC

Moving window

crosscheck

Yes

No

Moving window

crosscheck

Alarm

Controller triggerPoorly damped

mode detected?

Yes

No

OMS Flowchart

Event

Analysis

Engine

Damping

Monitor

Engine

Complementary Engines

Event Analysis Engine (EAE)

◦ Multiple algorithms

◦ Prony, Matrix Pencil, HTLS, ERA, and Multidimensional Fourier Ringdown Algorithm (MFRA).

◦ Aimed at events resulting in sudden changes in damping

Damping Monitor Engine (DME)

◦ Ambient noise based. Continuous. Provides early warning on poorly damped modes.

◦ Several algorithms

◦ Fast Frequency Domain Decomposition (FFDD), Distributed Frequency Domain Optimization (DFDO), and Recursive Adaptive Stochastic Subspace Identification (RASSI)

WSU Research Objectives

Oscillation Monitoring System for large power systems

Monitoring hundreds of PMUs simultaneously

System modes are changing – adaptive engines

Interactions with power electronics

Damping Monitor Engine – ambient data analysis

Event Analysis Engine – detection and analysis of

ringdowns and oscillations

Real-time engines and off-line engines

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Estimation Results

• Dominant modes are analyzed for each data set

• For each mode:

• Mode frequency

• Mode damping ratio

• Mode energy

• Mode shape

• Estimation confidence level

0.22 Hz WECC mode (well-damped)

0.38 Hz WECC mode (poorly damped)

June 13 2013 IPC Results

June 13th PSD Singular Values from WECC data

Mode Shape points to one generator

0.37 Hz at

Near Zero Damping Ratio

(7.30 am to 8.00 am)

0.4 Hz at

Near 8% Damping Ratio

(10 am to 11 am)

June 13th 0.37 Hz oscillations at Generator

Generator MW Forced Oscillations

•Operated in rough zone when wind power

output high.

•Vortex effect in Francis turbine when water flow

level is low

•Air compressor to keep oscillations low to nil

• 5 to 25 MW oscillations observed at 0.37 Hz

• Tricky for ambient mode monitoring engines

•Mode shape analysis critical

•Multi-dimensional analysis crucial

0.6 Hz Eastern system mode

Mode Identified using WSU OMS in Sept 2013 by Entergy PMU team led by Floyd

Mode seen in data from April 2013 and possibly in 2012

Mode damping averages around 4% and goes as low as 2%.

Has been reproduced by Entergy via SSAT

Mode not well observed Study in early stages

0.6 Hz Eastern system mode

OMS Mode Shape

TVA

SSAT Sunday, October 13, 2013, 20:10:13

SSAT 10.0 Testing_1.bin Powertech Labs Inc.

Copyright 2010 All rights reserved

Mode Shape Scatter

Real = -0.1515 1/s Imaginary = 3.7147 rad/s Frequency = 0.5912 Hz Damping = 4.08 %

Case: Testing_1.ssa Scenario: Inter Area Oscillations Contingency: No fault

Dominant State: 527161 : MUSTANG_13.8 : 0 : : Z : GENCLS : : Angle

Mode Shape Reference: 335075 : 1DYNEGY_18.0 : 0 : : 1 : GENROU : : Speed

Area 101 [ISO-NE ] Area 102 [NYISO ]

Area 103 [IESO ] Area 104 [TE ]

Area 105 [NB ] Area 106 [NS ]

Area 201 [AP ] Area 202 [ATSI ]

Area 205 [AEP ] Area 206 [OVEC ]

Area 207 [HE ] Area 208 [DEI ]

Area 209 [DAY ] Area 210 [SIGE ]

Area 212 [DEO&K ] Area 215 [DLCO ]

Area 216 [IPL ] Area 217 [NIPS ]

Area 218 [METC ] Area 219 [ITC ]

Area 220 [IPRV ] Area 222 [CE ]

Area 225 [PJM ] Area 226 [PENELEC ]

Area 227 [METED ] Area 228 [JCP&L ]

Area 229 [PPL ] Area 230 [PECO ]

Area 231 [PSE&G ] Area 232 [BGE ]

Area 233 [PEPCO ] Area 234 [AE ]

Area 235 [DP&L ] Area 236 [UGI ]

Area 295 [WEC ] Area 314 [BREC ]

Area 320 [EKPC ] Area 328 [PLUM ]

Area 330 [AECI ] Area 331 [BCA ]

Area 332 [LAGN ] Area 333 [CWLD ]

Area 339 [NLR ] Area 340 [CPLE ]

Area 341 [CPLW ] Area 342 [DUK ]

Area 343 [SCEG ] Area 344 [SC ]

Area 345 [DVP ] Area 346 [SOCO ]

Area 347 [TVA ] Area 349 [SMEPA ]

Area 350 [PS ] Area 351 [EES ]

Area 352 [YAD ] Area 353 [SEHA ]

Area 354 [SERU ] Area 355 [SETH ]

Area 356 [AMMO ] Area 357 [AMIL ]

Area 360 [CWLP ] Area 361 [SIPC ]

Area 362 [EEI ] Area 363 [LGEE ]

Area 364 [OMUA ] Area 366 [TAP ]

Area 401 [FPL ] Area 402 [PEF ]

Area 404 [GVL ] Area 406 [JEA ]

Area 407 [KEY ] Area 410 [NSB ]

Area 411 [FMPP ] Area 412 [SEC ]

Area 415 [TAL ] Area 416 [TECO ]

Area 417 [VER ] Area 418 [NUG ]

Additional areas are not printed due to

lack of space.-0.8

0.8

-0.6

0.6

-0.4

0.4

-0.2

0.2

0.2

-0.2

0.4

-0.4

0.6

-0.6

0.8

-0.8

TVA Entergy

SOCO

Entergy 5.5 Hz oscillations

Pattern different

on different

days

5.5 Hz oscillations

Actual Current Magnitude

seen in PMU

(From openHistorian)

OMS FDD 5 Hz mode

energy level captures the

change.

Entergy 5 Hz oscillations

Mode frequency changes during some days

5.45 Hz mode shape

5 Hz mode shape – different mode

-2

2.5

Event

Analysis

Damping

Estimate

PMU

Bus

Voltage

0

Summary

PMUs enabling technology for online oscillation analysis

Self-diagnosis: important to assess estimation quality

System changing: fast and adaptive engines needed.

Oscillation modes: analyze full bandwidth of signals.

Mode shape crucial for analysis: simultaneous

processing of all available PMUs recommended.

Distributed algorithms needed.