WAMS WACS.pdf - Nelson Martins

Wide-Area Monitoring and Control,
WAMS and BPA’s WACS, for
Enhanced Performance and Resilience
to Power Blackouts
Carson W. Taylor
Bonneville Power Administration (retired)
cwtaylor@ieee.org
CEPEL Roadmap Workshop
Florianópolis, SC. Brazil
20 May 2006

What is WAMS?
■ WAMS is monitoring of power system dynamic
performance:
• Mainly electromechanical and voltage dynamics
• RMS values or phasors, typical sampling at 20–60 Hz
• Fault recorders, oscillographs, power quality instruments
typically not part of WAMS
• Oriented towards centralized or networked monitoring
• Oriented towards continuous recording with archiving of
interesting events
• Term “WAMS” originated at BPA in late 1980s
• “WAMS” includes test and analysis techniques such as
the Fourier and Prony methods for system identification?
2

Better Information Supports Better Decisions
Disturbances
System planning
System operation
Automatic control
Source: John Hauer
Decision
Processes
Power
System
Information
Unobserved response
Observed response
Measurement
Based
Information
System
3

WAMS is More than Data
Wisdom
Knowledge
Information
Data
Operator needs
information, not data.
4

Source: John Hauer
WECC Phasor Network in
2005 (WAMS)
60 Phasor Measurement Units
(PMUs)
382 voltage or current phasors,
plus bus frequencies
8 Phasor Data Concentrators
(PDCs) at control centers
BCH
BPA
CAISO
PG&E
SCE
APS/SRP
PNM
WAPA
4 inter company data links
5

BPA Phasor Measurement System
V - I - F
Measurement
- substations
PMU
PMU
PMU
Direct
exchange with
other utilities
Source: Ken Martin
Data input &
management
- control center
Phasor Data
Concentrator
(PDC)
Correlates data,
feeds selected
applications,
monitors system
PDC
Operations
monitors – display
& alarms
SCADA - Voltage,
angle & frequency
Other displays -
Power World, etc.
StreamReader
Display & recording
Data storage
System
controls
Real-time
controls:
Voltage &
reactive
stability;
interarea
angle limits
6

BPA StreamReader, Loss of Colstrip, 6 Sept. 01
LabVIEW software, real-time display on PC. StreamReader computes
active and reactive power from phasors, etc.
7

BPA StreamReader: Time and Frequency Domain
Ambient activity, 7 June 2000. Source: John Hauer, PNNL
8

Eastern Interconnection Phasor Project
■ August 14, 2003 blackout reports had strong
recommendations for synchronized measurements
■ EIPP organization (http://phasors.pnl.gov):
• AEP, TVA, Entergy, Ameren, NYPA, DoE, NERC, PNNL, etc.
■ Four state estimator integration projects
• State measurements
• Texas A&M finding – Accuracy of state estimation
drastically improves by strategically placing PMUs at 10% of
the network buses
■ On-line efforts:
• Angular separation analysis and alarming
• Interarea oscillations
• Real-time stability applications
Source: Bob Cummings, NERC
9

EIPP Progress, 2005
■ 57 PMUs in Eastern Interconnection
• 24 more in next 12 months
• Over 400 digital relays – extending capability
■ 5 Phasor Data Concentrators
• Entergy, TVA, AEP, NYISO, Ameren
• Internet VPNs for communications
■ TVA Super PDC Operational
• Other PDCs connected
• 24 PMUs connected
■ On-Line Applications in testing
Source: Bob Cummings, NERC
10

Summary: Wide-Area Measurements [6]
■ Purpose: avoid system problems, not just record them.
■ Value: information has the same value as decisions
based upon it. Insurance against operational
uncertainties.
■ Applications: should support tests and analysis, and
real-time system operations
■ Event detection logic: trigger snapshot recordings or
apply to archived records.
• Continuous recording preferred; difficult to detect distant
events
■ Costs: Hardware is cheap, engineering time expensive
11

Power System Stability Controls
Local and Wide-Area
Power System
Disturbances
switch capacitor/reactor banks
direct
detection
(SPS) trip generators/loads
Discontinuous
Controls
response detection
(WACS)
Power
System
Dynamics
Continuous
Feedback
Controls
(generators)
12
∆ y

Event-Based Wide-Area Stability Controls
■ Special Protection System (SPS)/Remedial Action
Scheme (RAS)/Emergency Control
■ Many schemes in service, fast and reliable
■ Direct detection of pre-selected outages:
• Feedforward control
• Signal to central logic, then signal to power plant or
substation for action
• Generator/load tripping, reactive power compensation
switching
■ Complex, 24/7 RAS dispatcher
■ Expensive (high redundancy, hardware for each
potential outage). Recent cost of $575K for lineloss
logic at both ends of line with transfer trip to
two control centers.
13

Response-Based Wide-Area Stability Controls
■ Detect any disturbance by measured response
(feedback)
■ Improved observability and controllability
compared to local control
• Example: load shedding based on several voltages and
generator reactive power outputs rather than local
voltage
■ Continuous versus discontinuous controls
■ Continuous:
• “Wide-area PSS”
• Remote signals for control of HVDC, SVC, TCSC
14

Response-Based Wide-Area Stability Controls
■ Facilitated by IT:
• Digital sensors, communications, controllers
• Fiber optic communications
■ Time delays/latencies pose challenges:
• But control feasible for interarea oscillations
■ Example—low frequency mode with 3 second
period:
• Need first swing stabilization
• Impulse (short circuit) response peak at 0.75 second
• Step (line/generator outage) response peak at 1.5 second
15

Discontinuous Wide-Area Stability Controls
■ Response-based to stabilize large disturbances:
• First swing stabilization
• Reduce stress for improved damping
• Region of attraction/post-disturbance equilibrium
■ Generator/load tripping, capacitor/reactor bank
switching—powerful control actions:
• BPA has 550-kV capacitor banks up to 460 MVAr
■ Single switching action, or
■ True feedback—observe response, take action,
observe effect, take further action if necessary
■ SAFER than continuous control
• Biological system analogy—stimuli must be above
activation threshold
16

BPA Wide-Area Control System (WACS)
■ On-line demonstration uses existing wide-area
measurement systems (WAMS)
• Synchronized phasor measurement units (PMUs)
• Fiber optic communications
• 30 packets per second data rate (60 per second future?)
■ Existing Remedial Action Scheme (RAS) transfer trip
from control center to power plants and substations
available:
• Generator tripping and capacitor/reactor bank switching
■ Control computer(s) at control center(s):
• LabVIEW RT hardware and software (www.ni.com)
• Currently on-line at control center with real-time phasor
measurement inputs (monitor mode)
17

Latest Generation PMU
•Based on digital protective relay hardware and software
•60 packets/second data rate, adjustable data rate and filtering
•Used for new BPA installations — several vendors
18

Flexible Platform for Control
GPS
voltage phasors
current phasors
frequencies
fiber optics
SCADA
control center LAN
control
computers
BPA
control
center(s)
power
system
generator/load
tripping
reactive power
switching
Other actions

WACS — Flexible Platform for Control
20

Fiber Optic Latency
Delay in packets from Slatt PMU to control center PDC over one minute period.
PDC processing adds 5–6 ms.
21

WACS Computers, NI LabVIEW RT
RT Engine (Networked to
the Power System Phasor
Measurement Units)
Connection Interface to the
Transfer Trip
Communications Network
Host PC (Networked to the
RT Engine)
22

WACS Laboratory Installation
23

Source: John Hauer
WACS Inputs
12 PMU voltage magnitude
measurements from:
Malin
Captain Jack (2 busses)
Summer Lake (2 busses)
Slatt (2 busses)
Ashe (2 busses)
John Day
McNary 500 (2 busses)
PMU-derived generator reactive
power measurements from:
John Day (4 generator lines)
Big Eddy (4 generator lines)
McNary (5 generator lines)
Ashe (Columbia Gen. Station)
Slatt (Boardman plant)
Calpine Hermiston
BPA fiber optic communications
(SONET)

Why Not Use Voltage Phase Angles?
■ Under study for future [1, Appendix III]
■ Reliable, high speed signals not available from
other utilities
■ Voltage phase angle susceptible to GPS glitches
■ Voltage magnitudes near swing center closely
related to angle difference swings
■ Voltage phase angles state variable for steadystate
analysis (power flow program) but not for
dynamics
25

for high BC exports
26

Two Algorithms
AC Intertie
Pacific NW
to California
First swing (spring)
Vmag or VmagQ algorithm
Simultaneous
Transfer
Nomogram
North to South flow in Washington state
High flow means generation farther away
Ensure RoA and
post disturbance
secure operation
VmagQ algorithm
Damping (summer)
Vmag or VmagQ
algorithm
27

Voltage Magnitude (Vmag) Algorithm
■ Control accumulates volt-seconds of weighted
average voltage from twelve 500-kV measurements:
• Like inverse-time undervoltage relay
• Accumulation (integration) starts when weighted voltage
decays below threshold. No accumulation if present input is
higher than previous
• Control action when accumulation reaches setpoint and
weighted voltage level is below a setpoint
• Accumulator resets if weighted voltage recovers
• Time frame of around one second
■ Separate accumulators for generator tripping and
500-kV reactive power compensation switching
28

Vmag Algorithm Block Diagram for Simulation
Voltage magnitude inputs, weights,
and number of bus measurements
Malin 1.0 01
Captain Jack 1.0 02
Summer Lake 1.0 02
Slatt 0.5 02
John Day 0.5 01
McNary 500 0.2 02
Ashe 0.2 02
Sum 7.3 12
V
W
Arrays (vectors) of 12 voltages
and weights. Valid voltage
ranges are 360–650 kV.
∑ × Vi
Wi
W
∑
V Threshold
520 kV for gen. trip,
525 kV for cap./reactor switching
i
V Avg
Notes:
1. Individual computations and settings for each controlled device.
Currently we use identical settings for all generator tripping locations,
and different identical settings for all capacitor/reactor switching
locations. Identical voltage magnitude weights are used for all devices.
2. Current settings are shown. Latest settings are on ini file.
3. Accumulation is blocked if present VAvg greater than VAvg of last
execution cycle. Reset when VAvg recovers above VThreshold .
-
+
0
HV
Gate
Accumulator
Setpoint
4 kV-seconds for gen. trip
2 kV-seconds for cap./reactor switching
Σ( .
)∆t
Accumulator
Note 3
V supervise
0
<
1
&
490 kV for gen. trip
520 kV for cap./reactor switching
Control
Output
29

Simulation Example: Transient Stability
■ Outage of nuclear units in south:
• Two Palo Verde units, 2700 MW
• Inertia and governor action in north loads North–South
intertie
■ Use WACS to extend Pacific intertie transfer
capability:
• Example show gain of 300 MW (4700 MW to 5000 MW)
30

for high BC exports
31

Existing controls, 4700 MW intertie loading
Malin
500-kV voltages
575 kV
550 kV
525 kV
500 kV
475 kV
450 kV
425 kV
Two Palo Verde outage at one second (2710 MW), Reactive power switching
at Malin, Fort Rock at 2.33–2.8 s.
32

w/WACS, 5000 MW intertie loading
Malin
500-kV voltages
575 kV
550 kV
525 kV
500 kV
475 kV
450 kV
425 kV
Two Palo Verde outage at one second (2710 MW), generator dropping at
Shrum and Mica (916 MW) at 2.4 s, reactive power switching a Malin, Marion,
Fort Rock at 2.2–2.6 s (FACRI and WACS). Base case for sensitivities.
33

Voltage/Reactive Power (VmagQ) Algorithm
■ Generator reactive power outputs are sensitive
indicators of voltage problems
■ Combine using fuzzy logic:
• Weighted voltage magnitude measurements
• Weighted generator reactive power measurements
• Output accumulators similar to Vmag algorithm
■ Reactive power capability is function of active power:
• P, Q measurements from PMUs located at transmission side
• Normalization based on max, min limits
■ Time frame of second (first swing) to tens of seconds:
• Longer-term dynamics: OELs, LTCs, etc.
• Capacitor/reactor bank switching first, followed by generator
tripping as necessary
34

VmagQ Algorithm
V i
Station
measurements
Q gj
Input
processing
u m Defuzzification
(Center of
Gravity)
Normalization
and
weighted
values
u m *
V m
Q gm
Accumulators
and
threshold
logic
Fuzzy
logic
control
To
compensation
stations
and
power plants

Fuzzy Set for Weighted Voltage
36

Fuzzy Set for Weighted Reactive Power
37

Output Fuzzy Set
38

VmagQ Algorithm Fuzzy Logic Rules
Q Avg
PLq
PMq
OKq
NMq
NLq
PLo
1.0
PLo
0.8
PMo
1.0
PMo
0.8
PSo
1.0
5
4
3
2
1
PLo
0.8
PMo
0.8
PSo
1.0
PSo
0.8
ZEo
1.0
10 15
9
8
7
6
PMo
0.5
PSo
0.5
ZEo
1.0
ZEo
1.0
ZEo
1.0
ZEo
1.0
ZEo
1.0
ZEo
1.0
ZEo
1.0
11 16
ZEo
1.0
ZEo
1.0
ZEo
1.0
ZEo
1.0
ZEo
1.0
21
ZEo
1.0
VLOv LOv OKv HIv VHIv
14
13
12
20 25
19
18
17
24
23
22
V Avg
Lower case v, q, o indicate voltage,
reactive power, and output
VLO - Very Low
LO – Low
HI – High
VHI – Very High
NL – Negative Large
NM – Negative Medium
NS – Negative Small
ZE – Zero
PS – Positive Small
PM – Positive Medium
PL – Positive Large
There is no control for high voltage so
inactive rules are set to ZE.
The large number in each cell is the
Degree of Support or weight of the
rule (range is 0 to 1). The small
number is the rule number.
39

Rulebase Editor
40

I/O Characteristic, Weighted Q = 0.5 pu
41

WACS Status
■ R&D largely complete with proof of concept, code
verification, and tuning
■ Three years on-line laboratory and control center
monitoring
■ Playback of simulation and archived PDC data
■ BPA deciding on full deployment (~$1.5M):
• Business case in preparation
• Design for WECC certification, new PMUs, SONET
communication expansion, controllers at both control
centers, O&M training, spare parts
42

WACS for Voltage Stability
■ Presently WACS oriented toward angle stability
for export conditions; BUT…
■ Flexible platform with two existing algorithms
that could be used for load shedding:
• Voltage magnitude based similar to inverse-time relays
• Combination of voltage and generator reactive power
(applicable to August 14, 2003 blackout)
■ WACS could be used for other voltage collapse
countermeasures:
• Capacitor/reactor bank switching
• Tap changer blocking, runback, or reverse control
• Boost of high side voltage schedule
43

WACS Business Case: Potential Benefits
1. Increased reliability:
• Control for disturbances anywhere in interconnection
• Additional layer of defense: Defense in Depth
• As feedback control, compensate for simulation and
operational uncertainties
• Blackouts happen and cost billions
2. Increased transfer capability, ~300 MW in one
example
3. Flexible, open system platform for rapid control
and monitoring applications
• Future potential with IT advances
• Use of voltage phase angles throughout interconnection
4. Future partial replacement for costly event-
driven RAS
44

Reference
1. C. W. Taylor, D. C. Erickson, K. E. Martin, R. E. Wilson, and V.
Venkatasubramanian, “WACS—Wide-Area Stability and Voltage
Control System: R&D and On-Line Demonstration,” Proceedings of
the IEEE special issue on Energy Infrastructure Defense
Systems, Vol. 93, No. 5, pp. 892–906, May 2005.
45

Questions?
46