1 Spring 2016 Instructor: Kai Sun ECE 692 Advanced Topics on Power System Stability Remedial Action Scheme (RAS) / Special Protection System (SPS)
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Spring 2016
Instructor: Kai Sun
ECE 692 Advanced Topics on
Power System Stability
Remedial Action Scheme (RAS) / Special Protection System (SPS)
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Content
•SPS/RAS Overview:
– Definitions, functions, standards and categories
•Examples
– Vendor solutions
– Utility implementations
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References1. “Remedial Action Scheme” Definition Development: Background and Frequently Asked Questions, NERC, June
2014
2. Western Electricity Coordinating Council (WECC), Remedial Action Scheme Design Guide, prepared by RelaWork Group, October 2005. http://www.wecc.biz/committees/StandingCommittees/OC/TOS/RWG/Lists/Calendar/Attachments/10/20-RAS_Guide_clean2.pdf
3. GARD 8000 Remedial Action Scheme (RAS) Module Flyer, RFL Electronics Inc. http://www.rflelect.com/pdf_files/GARD_RAS_1-09.pdf
4. Schweitzer Engineering Laboratories – Power Management Solutions. http://www.selinc.com/engineeringservices/PowerManagementSolutions/
5. Centralized Remedial Action Scheme, Southern California Edison Company., July 23, 2009.
6. Introduction to On-line SPS. Hitachi Ltd. Apr. 2012.
7. 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.
8. 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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a. Out‐of‐step tripping and power swing blocking (a protection function)
b. Automatic under-frequency load shedding (UFLS) programs (a protection function having unique design and implementation considerations covered by another NERC standard)
c. Under-voltage Load Shedding Programs (UVLS Programs) (a protection function addressed in another NERC standard)
d. Auto-reclosing schemes (unless being integrated into a larger system performing additional corrective actions to accomplish objectives of a RAS)
e. Schemes applied on an Element for non‐Fault conditions to protect it from damage (a protective function)
f. Local controllers that switch or regulate an Element, e.g. reactive devices, FACTS, phase-shifting/variable frequency/TC transformers, or generation excitation
g. Remote FACTS controllers that switch static shunt reactive devices located at other stations to regulate the output of a single FACTS device
Controllers/schemes that do not individually constitute a RAS [1]:
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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 under-voltage‐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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3
1
2
3
1GW generation
tripped by SPS
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4
Faulty zone 3
relay
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5
6 8
67
7
8
Loss of key
hydro units
Tripped by
Zone 3 relay
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9
10
Tree
contact
and
relay
mis-opt.
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 PRC-017-0 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]
SEL-2030
Logic Processor SEL-2100
RTU
MAIN
EMS Computer
Automatic Arming
Program (AAP)Local Arming
Switch
Mira Loma Chino Padua
RCC
EMS Computer
Lugo Rancho Vista
F-35
RASLugo
Victorville
Mira Loma
EtiwandaOntario
Chino
Padua
Serrano
Rancho Vista
GCC Mira Loma
FiberMicrowave
Hardwired
Communication
Processor
SEL-351 SEL-351 SEL-351
Mitigation
SEL-351
F-35
SEL-351
F-35
SEL-351
Line Monitoring
Configuration of Existing RAS
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MAIN
EMS Computer
Mira Loma Chino PaduaLugo Rancho Vista
GCC / AGCC
FiberMicrowave
Hardwired
Triple
Redundant
Servers
ICCP
Monitor
Line Monitoring Mitigation
Configuration of Centralized RAS
Centralized RAS of SCE
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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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