Upload
others
View
19
Download
0
Embed Size (px)
Citation preview
Power System Oscillations
Overview
Mani V. Venkatasubramanian
Washington State University
Pullman WA
Stability Mechanisms
• 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
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
TVA, Entergy, Peak RC
Southern CO
Entergy, Southern CO
4
Inter-Area Oscillations
Powerworld Animation © Washington State University
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 5
© Washington State University
August 10, 1996 western event
• Three 500 kV lines out
• 14.01 to 14.52: Two 500 kV lines tripped owing to faults. Damping drops from high to low
• 15.42: 500 kV Keeler-Alston line tripped: Damping drops to near 3%
• 15.47: 230 kV Ross-Lexington line trips. Poorly damped inter-area oscillations start. Additional trippings. Growing oscillations. Blackout.
© Washington State University
6
August 10, 1996 Sequence of Events
• Heavy summer loading conditions
• Low voltages in Pacific Northwest
• 15.42 PDT: Trip Keeler 500 to Allston
500 (Case 0)
• 15.47 PDT: Trip a) Ross 230 to
Lexington 230, b) St.John 115 to View
Tap 115 and c) Swift generator (200
MW) (near Portland) (Case 1)
© Washington State University
August 10, 1996 Sequence of Events
• McNary generation starts tripping from faulty field protection relay. Oscillations appear. (Case 2)
• 15.48 PDT: Nearly all McNary units trip out. AGC ramps up Coulee, John Day generation for load balancing. Oscillations grow. (Case 3)
• 200 MVAR Cap bank switched in at Malin 500. (Case 4). Little effect. COI lines tripped. Blackout.
© Washington State University
August 10, 1996 Sequence of Events
Case
0
Case
1
Case
2
Case
3
Case
4
© Washington State University
August 10, 1996 event
Analysis of Validated Model
Small-signal
Stable
Small-signal
Unstable
0.25 Hz inter-area mode changed from +2%
positive damping to -2% negative damping© Washington State University
Entergy, Southern COEntergy, Southern CO
Two Types of PMU Analysis Engines
Event Analysis
0.4 Hz at +10% damping. Inter-Area Mode.
Ambient Noise Analysis
0.4 Hz at +10% damping. Inter-Area Mode.
© Washington State University
PMU Data Analysis of
Aug 10 1996 event
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
Frequency
(Hz)
Damping
Ratio (%)
Prony 0.2651 3.17
Matrix
Pencil0.2664 2.41
HTLS 0.2664 2.40
20 s data of Malin- Round Mountain MW
after the first tripping
© Washington State University
13
Before Keeler-Allston trip
150 200 250 300 350 4000
0.5
1
1.5
Time (s)
Fre
qu
en
cy (
Hz) Frequency Estimates
150 200 250 300 350 4000
2
4
6
8
Time (s)Da
mp
ing
Ra
tio (
%)
Damping Ratio Estimates
Mode Damping near 6% before Keeler-Alston trip
© Washington State University
After Keeler-Alston trip
600 620 640 660 680 700 7200
0.5
1
1.5
Time (s)
Fre
qu
en
cy (
Hz) Frequency Estimates
600 620 640 660 680 700 7200
2
4
6
8
Time (s)Da
mp
ing
Ra
tio
(%
)
Damping Ratio Estimates
© Washington State University
Mode Damping near 2% after Keeler-Alston trip
Oscillations
Natural Mode Oscillations, Forced Oscillations
Well-damped oscillations, Poorly damped oscillations, undamped oscillations, growing oscillations
Cause fatigue in rotor shafts, Reduces rotor life
Power quality concerns
Undesirable tripping of generation units or curtailment
Resonance effect with inter-area modes
Can lead to blackouts
© Washington State University
16
Well-damped oscillations
Powerworld Animation © Washington State University
17
Poorly Damped Oscillations
Powerworld Animation © Washington State University
18
Local oscillations
Powerworld Animation © Washington State University
June 17 2016 Mississippi event
© Washington State University
19
© Washington State University
Oscillation Monitoring
Oscillation Monitoring System for WECC and Entergy
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
© Washington State University
Oscillation Monitoring System
OpenPDC
OMS
OMS real-time version built into OpenPDC.
Off-line version available as stand-alone programs.
IEEE C37.118
BPA PDCstream
Real-time PMU
data streamOMS results
Oscillation
Monitor
openPDC
SQL server
Calculated
measurements
© Washington State University
Fast Frequency Domain
Decomposition (FFDD)
– Collect and preprocess signals from PMUs
– Power spectrum estimation by FFT and Multi-
Taper Method
– Apply SVD on the power spectrum
• Approximate the largest singular value by the trace of
the power spectrum matrix (Fast FDD)
– Apply inverse FFT on largest singular values
– Extract pole frequency and damping ratio
from exponential form by ringdown analysis
– Can process 1000+ signals simultaneously.© Washington State University
Medium Resonance on November 29, 2005
• 20 MW 0.27 Hz Forced Oscillation in Alberta Canada.
• System mode 0.26 Hz at around 7% damping.
• 200 MW Oscillations on California-Oregon Inter-tie.
• Resonance Amplification Factor = 10.
• Recent IEEE Trans. paper
Thanks to Greg Stults (BPA) and Jim Burns (BPA)
© Washington State University
June 17 2016 Mississippi event
© Washington State University
24© Washington State University
Oscillations Summary• Inter-Area Oscillations can be devastating. Forced
Oscillations are problematic…
•August 10, 1996 – WECC blackout caused by oscillations
•Nov 29, 2005 Alberta event - resonance between forced oscillation and (0.25 Hz) inter-area mode.
• Sept 5, 2015 Nevada event –resonance between forced oscillation and (0.4 Hz) inter-area mode.
• June 17, 2016 oscillation event in the east.
• Inter-Area Resonance – potential risk for
operational reliability of the grid
•Urgent need to analyze oscillation sources
and work on damping controllers25