ECE 692
Advanced Topics on
Power System Stability
Remedial Action Scheme (RAS) /
Special Protection System (SPS)
Spring 2016
Instructor: Kai Sun
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Content
•SPS/RAS Overview:
– Definitions, functions, standards and categories
•Examples
– Vendor solutions
– Utility implementations
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References
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8.
“Remedial Action Scheme” Definition Development: Background and Frequently Asked Questions, NERC, June
2014
Western Electricity Coordinating Council (WECC), Remedial Action Scheme Design Guide, prepared by Rela
Work Group, October 2005.
http://www.wecc.biz/committees/StandingCommittees/OC/TOS/RWG/Lists/Calendar/Attachments/10/20RAS_Guide_clean2.pdf
GARD 8000 Remedial Action Scheme (RAS) Module Flyer, RFL Electronics Inc.
http://www.rflelect.com/pdf_files/GARD_RAS_1-09.pdf
Schweitzer Engineering Laboratories – Power Management Solutions.
http://www.selinc.com/engineeringservices/PowerManagementSolutions/
Centralized Remedial Action Scheme, Southern California Edison Company., July 23, 2009.
Introduction to On-line SPS. Hitachi Ltd. Apr. 2012.
D. Lefebvre, S. Bernard, and T. Van Cutsem, Undervoltage Load Shedding Scheme for the Hydro-Québec System.
IEEE PES General Meeting, Denver CO, June 2004.
S. Kolluri, K. Tinnium, and M. Stephens, Design and Operating Experience with Fast Acting Load Shedding
Scheme in the Entergy System to Prevent Voltage Collapse. IEEE PES Winter Meeting, 2000
http://ewh.ieee.org/soc/pes/psdpc/documents_UVLS_panel/Sharma_Kolluri.pdf
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NERC Definition of a Protection System [1]
•Protective relays which respond to electrical quantities,
•Communications systems necessary for correct operation of protective functions,
•Voltage and current sensing devices providing inputs to protective relays,
•Station dc supply associated with protective functions (including batteries, battery
chargers, and nonbattery‐based dc supply), and
•Control circuitry associated with protective functions through the trip coil(s) of the
circuit breakers or other interrupting devices.
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NERC Definition of Remedial Action Scheme (RAS) [1]
•RAS is a scheme designed to detect predetermined System conditions and
automatically take corrective actions that may include, but are not limited to,
curtailing or tripping generation or other sources, curtailing or tripping load, or
reconfiguring a System(s).
•RAS accomplish one or more of the following objectives:
–
–
–
–
–
–
Meet requirements identified in the NERC Reliability Standards;
Maintain System stability;
Maintain acceptable System voltages;
Maintain acceptable power flows;
Limit the impact of Cascading; or
Address other Bulk Electric System (BES) reliability concerns.
•RAS is not a Protection System; however, it may share components with Protection
Systems.
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RAS vs SPS
•Currently, both SPS and RAS are used in the eight NERC Regions.
•Document [1] has recommended that the term RAS be retained as
the industry‐recognized term and that the term SPS be retired.
•The term RAS is more descriptive of the purpose for which the
scheme is installed.
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Controllers/schemes that do not individually constitute a RAS [1]:
a.
b.
c.
d.
e.
f.
g.
Out‐of‐step tripping and power swing blocking (a protection function)
Automatic under-frequency load shedding (UFLS) programs (a protection function having unique
design and implementation considerations covered by another NERC standard)
Under-voltage Load Shedding Programs (UVLS Programs) (a protection function addressed in another
NERC standard)
Auto-reclosing schemes (unless being integrated into a larger system performing additional
corrective actions to accomplish objectives of a RAS)
Schemes applied on an Element for non‐Fault conditions to protect it from damage (a protective
function)
Local controllers that switch or regulate an Element, e.g. reactive devices, FACTS, phaseshifting/variable frequency/TC transformers, or generation excitation
Remote FACTS controllers that switch static shunt reactive devices located at other stations to
regulate the output of a single FACTS device
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Controllers/schemes that do not individually constitute a RAS (cont’d):
h. Remote schemes/controllers switching shunt reactors/capacitors for voltage regulation that would
otherwise be manually switched (not remedial in the sense of being mitigations in response to
predetermined system conditions, but for general application to all system conditions)
i. Schemes automatically de‐energizing a line for a non‐Fault operation when one end opens
j. Schemes that provide anti‐islanding protection (e.g., protecting load from effects of being isolated
with generation that may not be capable of maintaining acceptable frequency and voltage)
(designed to protect load; actions taken on islanded facilities will not impact the BES any more)
k. Automatic sequences that proceed when manually initiated solely by an operator (because the
decision to active a specific sequence is left to the operator)
l. Modulation of HVDC/FACTS via supplementary controls such as angle damping or frequency
damping applied to damp local or inter‐area oscillations (like a PSS, this is not classified as RAS)
m. Sub‐synchronous resonance (SSR) protection schemes that directly detect sub‐synchronous
quantities (e.g., currents or torsional oscillations)
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On Undervoltage Load Shedding (UVLS) [1]
•Undervoltage Load Shedding (UVLS) Program: An automatic load shedding program
consisting of distributed relays and controls used to mitigate under-voltage
conditions leading to voltage instability, voltage collapse, or Cascading outages
impacting the Bulk Electric System (BES). However, centrally controlled undervoltage‐based load shedding is not included.
•The design and characteristics of centrally controlled undervoltage‐based load
shedding are categorized as RAS (wherein load shedding is the remedial action).
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Overview of RAS Objectives and Control Methods [2]
2. WECC Remedial Action Scheme Design Guide,
prepared by Rela Work Group, October 2005.
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Some Statistics
• IEEE PSRC Report on Global Industry Experiences with System Integrity Protection Schemes (SIPS)
Throughput time of the entire scheme
• Below 50 ms (2)
• Below 60 ms (0)
• Below 70 ms (2)
• Below 80 ms (1)
• Below 90 ms (1)
• Below 100 ms (3)
• Below 110 ms (blank)
• Between 110 – 150 ms (2)
• Between 150 – 200 ms (7)
• >200 ms (11)
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Overview of RAS – Categories
•Event-based RAS
– Directly detect outages and/or fault events and initiate actions
– Open-loop control
•Parameter-based RAS
– Measure variables for which a significant change confirms the occurrence of a critical event
– Open-loop control but with indirect event detection - the measured variables may include power,
angles, etc., and/or their derivatives.
•Response-based (adaptive) RAS
– Monitor system response during disturbances and incorporate a closed-loop process to react to actual
system conditions
– Require finely calibrated to the magnitude of the disturbance, but usually is not fast enough to
prevent instabilities following severe disturbances
– E.g. Fast Acting Capacitor and Reactor Insertion (FACRI) against voltage decline near the COI of WECC
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7
4
Tripped by
Zone 3 relay
Faulty zone 3
relay
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2
5
6 8
3
1GW generation
tripped by SPS
1
Tree
contact
and
relay
mis-opt.
Loss of key
hydro units
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1
2
4
5
6
7
9
8
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Example of Voltage Collapse July 2nd, 1996 Western
Cascading Event
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Examples on SPS/RAS failures
1. July 2, 1996, WECC (formerly known as WSCC) Blackout.
– Cause: Logic Error – Multiple SPSs unable to respond in coordinated fashion
– Description: Two parallel lines were tripped to which SPS responds by correctly tripping some generation.
Another two simultaneous line trips, one of which was caused by a relay acting correctly based on local
operating instructions, caused voltage instability and subsequent system collapse. More coordination
between the two remedial actions might have prevented this blackout.
– Mitigation Strategy: Implementing coordinated SPS systems that can take system-level actions based on
data from across the system.
2. May 3, 2003, Hydro-Quebec, TransEnergie (Canada)
– Cause: Hardware Failure causing Incorrect Settings
– Description: The SPS main computer was removed from system due to a problem. As a result, default set
points for generators were used as set points. A transmission line tripped and SPS acted based on the
default set points rather than the actual generation levels for that day.
– Mitigation Strategy: Ensure procedures are in place for removal of SPS components for maintenance
without causing SPS malfunction.
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NERC Standards Related to SPS/RAS
• PRC-004-WECC-1 Protection System and Remedial Action Scheme Mis-operation (WECC): This is a
Regional Reliability Standard to ensure all transmission and generation Protection System and Remedial
Action Scheme (RAS) Mis-operations on Transmission Paths and RAS defined in section 4 are analyzed
and/or mitigated.
• PRC-012-0 Special Protection System Review Procedure: To ensure that all SPSs are properly designed,
meet performance requirements, and are coordinated with other protection systems. To ensure that
maintenance and testing programs are developed and mis-operations are analyzed and corrected.
• PRC-013-0 Special Protection System Database: To ensure that all SPSs are properly designed, meet
performance requirements, and are coordinated with other protection systems.
• PRC-014-0 Special Protection System Assessment: To ensure that all SPSs are properly designed, meet
performance requirements, and are coordinated with other protection systems. To ensure that
maintenance and testing programs are developed and mis-operations are analyzed and corrected.
• PRC-015-0 Special Protection System Data and Documentation, PRC-016-0 SPS mis-operations, and PRC017-0 Special Protection System Maintenance and Testing: To ensure that all SPSs are properly designed,
meet performance requirements, and are coordinated with other protection systems. To ensure that
maintenance and testing programs are developed and mis-operations are analyzed and corrected.
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Vendor solution: RFL Electronics Inc. [3]
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Vendor solution: Schweitzer Engineering Lab (SEL) [4]
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Utility example: Southern California Edison (SCE)[5]
Configuration of Existing RAS
Victorville
GCC
Mira Loma
RCC
EMS Computer
MAIN
EMS Computer
Rancho Vista
RTU
Automatic Arming
Program (AAP)
SEL-2030
Etiwanda
Ontario
Chino
Mira Loma
Serrano
Logic Processor SEL-2100
Mitigation
Line Monitoring
SEL-351
Padua
Communication
Processor
Local Arming
Switch
Fiber
Microwave
Hardwired
Lugo
RAS
SEL-351
F-35
F-35
Lugo
Rancho Vista
SEL-351
SEL-351
SEL-351
SEL-351
Chino
Padua
F-35
Mira Loma
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Centralized RAS of SCE
Configuration of Centralized RAS
GCC / AGCC
ICCP
Monitor
MAIN
EMS Computer
Triple
Redundant
Servers
Mitigation
Line Monitoring
Lugo
Rancho Vista
Fiber
Microwave
Hardwired
Mira Loma
Chino
Padua
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Utility example: Chubu Electric Power Co., Inc., Japan (CEPCO) [6]
•Transient Stability Control (TSC) system implemented in 1995
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Utility example: TDST (UVLS) in Hydro Québec (HQ) [7]
• Designed to operate during extreme conditions involving outages of
two or more 735kV lines in Montreal area, which can cause long-term
voltage instability.
• The average voltage V is used when 3 valid measurements of 5
substations are received; for the most severe disturbances, 3 steps will
be used to shed up to 1500MW load:
– Rule R1: if V<0.94pu for 11 seconds, shed 400 MW
– Rule R2: if V<0.92pu for 9 seconds, shed 400 MW
– Rule R3: if V<0.90pu for 6 seconds, shed 700 MW
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Utility example: VSHED (UVLS) in Entergy [8]
Western Region PV curves
Western Region
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•VSHED was first implemented in 1998
– Obtains information directly from SCADA
system via a communication path from
the problem location to the control room
– Activated automatically when the load of
the Western Region reaches a certain
level
– Quickly detects voltage collapse,
recognizes heavy VAR demand on
generating units and sheds load in blocks
at desired locations
– Remote tripping of breakers without
manual intervention
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