RAS Type Definitions

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					                            WECC SIPS / RAS PRC Compliance

                                  i-PCGRID Workshop 2009

                                        Gene Henneberg
                                        March 20, 2009

Introduction
The Western Electricity Coordinating Council (WECC) is one of eight Regional Reliability
Organizations (RROs) in North America whose responsibilities include oversight of the
compliance of its members with many of the NERC standards. The RROs also have specific
compliance responsibilities directly to NERC under these Standards. Each standard identifies
the party to whom it applies.

This paper describes how the WECC complies with the NERC standards that regulate Special
Protection Systems (SPS). These protection systems are also known as Remedial Action
Schemes (RAS) or, more recently, System Integrity Protection Schemes (SIPS). This paper
uses the term in most common use by individual RROs when discussing a specific RRO. Within
the WECC, that term is. RAS, while the other RROs generally use SPS.

NERC Standards for RAS
The NERC glossary defines a Special Protection System (SPS) as
   An automatic protection system designed to detect abnormal or predetermined system
   conditions, and take corrective actions other than and/or in addition to the isolation of faulted
   components to maintain system reliability. Such action may include changes in demand,
   generation (MW and Mvar), or system configuration to maintain system stability, acceptable
   voltage, or power flows. An SPS does not include (a) underfrequency or undervoltage load
   shedding or (b) fault conditions that must be isolated or (c) out-of-step relaying (not
   designed as an integral part of an SPS). Also called Remedial Action Scheme.

This broad definition seems to cover virtually every protection system that is not intended to
isolate faulted components, with a few stated exceptions.

The NERC standards that pertain most specifically to RAS are under the Protection and Control
(PRC) category, PRC-012 through PRC-017. PRC-012 – PRC-014 identify the responsibilities
of the RROs and PRC-015 – PRC-017 identify the responsibilities of the scheme owners. The
general purposes for all of these standards is to ensure that RAS
 are properly designed,
 meet performance requirements,
 are coordinated with other protection systems,
 maintenance and test programs are developed, and
 misoperations are analyzed and corrected.

The PRC-012 standard refers to the system performance requirements of NERC standards
TPL-001-0, TPL-002-0, and TPL-003-0. These Transmission Planning standards identify
required transmission system performance for simultaneous loss of up to two or more elements.
PRC-012 requires that RROs establish appropriate RAS review procedures and is the
foundation on which standards PRC-013 – PRC-017 are built.



                                                 1
None of these ―RAS‖ standards PRC-012 – PRC-017 refer directly to the Bulk Electric System.
Only PRC-012 refers to the TPL transmission performance standards, TPL-001-0 – TPL-003-0
(but not to TPL-004-0). Standards PRC-013 – PRC-014, and PRC-017 do not refer to other
standards and standards PRC-015 and PRC-016 refer back only to PRC-012 and PRC-013.

Regional Practices
Each RRO has developed its own procedure to review and approve its member’s RAS (SPS).
Some RROs use a few individuals from separate technical groups that have responsibilities for
Planning and Protection issues as their review committee. Other RROs use their full technical
committees for separate reviews, with at least one additional level of review before approvals.
Many specific scheme review procedures vary among the RROs. Table I provides a summary
of the procedures and related documents publicly available on each RRO’s web site [1 – 13].

Most of the variation among the RRO’s RAS review procedures is within a relatively small
range. All RRO procedures describe their review process and other information that RAS
owners must provide to describes individual schemes. Each RRO compiles a data base of the
appropriate RAS within its area and assesses the effectiveness of the RAS it reviews.

However, in one significant area, two RROs differ from the others. This difference is in the
scale of the individual schemes that is recognized and factored into the review procedures.

While sub-categories of RAS are not the general rule among RROs, such a division seems to
be anticipated by the TPL standards. The TPL-004 standard covers extreme (multiple
contingency) system events, including cascading outages. TPL-004-0 requires that such
extreme events be studied, but does not require remediation. Any protection systems designed
to address the TPL-004 performance standard are not covered under the PRC-012 standard.

Similarly, Table 1, Note b) (part of all TPL-001-0 – TPL-004-0 standards) recognizes that
―interruption of electric supply to radial customers or some local Network customers may occur
in certain areas without impacting the overall reliability of the interconnected transmission
systems.‖ Protection systems intended to remediate events in such ―certain areas‖ of ―local
Networks‖ are recognized by the TPL standards to not impact the reliability of the
interconnected transmission systems.

The Northeast Power Coordinating Council (NPCC) and WECC both recognize these
distinctions. The specific terminology used by these RROs differs, but the classifications
defining each type of scheme are very similar. This categorization allows a more direct focus on
schemes that have a larger impact on reliability of the interconnected transmission systems.

The NPCC has recognized and classified three Types (I, II, and III) of RAS (SPS), at least since
the late 1990’s. These definitions (8,9,10) are summarized as follows:
 Type I:      Failure or misoperations would have significant impact outside the local system,
 Type II:     Remediates extreme contingencies or other extreme causes where failure or
    misoperation would have significant impact outside the local system, and
 Type III: Failure or misoperations would not have significant impact outside the local
    system.
NPCC also ties these scheme definitions to their specific definitions in the NPCC glossary of the Bulk
Power System, Significant Adverse Impact, and the Local Area.

Originally NPCC required review only of Type I and II schemes, though NPCC’s most recent
procedure also requires a limited NPCC review of Type III schemes. Still, the Type III review


                                                  2
primarily confirms the local scope of the specific scheme and is not at the same level of detail as
reviews of Type I and II schemes. The design practices required for a Type I SPS are
encouraged, but not required for a Type III SPS. A few of the Type I criteria also do not apply to
the Type II scheme because the Type II scheme is installed at the NPCC member’s discretion.

WECC has also recognized similar scheme differences in its RAS review procedures [1] which
classifies remedial action schemes that require detailed WECC review, similar to NPCC Type I
schemes, as
        . . . those schemes for which failure would result in bulk transmission system
        performance in a neighboring facility outside the limits of the WECC performance
        requirements.

Conversely, if performance outside accepted limits is confined to a local area, a protection
system to mitigate those conditions is considered as one having only local impact. This
definition is closely equivalent to NPCC’s Type III scheme definition. WECC also classifies as a
Safety Net a scheme that mitigates unforeseeable, extreme system events. This is closely
equivalent to NPCC’s Type II scheme definition.

WECC Historical Practices
WECC and its members have used RAS extensively for many years to ensure system reliability.
One member with many RAS maintains a specific RAS design group and assigns a dispatcher
specifically for RAS operation on the day shift. Recent experience with new generation plants
and the often limited ability to build major new transmission facilities to accommodate those
plant’s in-service schedules has further increased dependence on RAS. This particular
phenomena also seems to be well known with other RROs. The scale of the possible remedial
actions for all RAS ranges from simple direct-trip schemes to some of the largest and most
complex schemes in the world.

The Technical Studies Subcommittee (TSS) oversees regional Transmission Planning functions
within WECC, including an annual study program and tracking projects under the Regional
Planning and Rating Review process. These studies and reviews typically identify the need for
RAS having a significant regional impact, including Safety Nets. The affected owners and
Planning Authorities, subject to TSS review, perform the system studies necessary to identify
the characteristics of regional-scale RAS, and identify scheme parameters such as critical
system conditions, appropriate remedial actions, and required timing of those actions.

Requirements for less-extensive RAS are typically identified by individual owners or Planning
Authorities, along with the appropriate scheme parameters. Requirements for local schemes
are normally identified at this level.

The WECC has assigned a specific group to review RAS implementation since the mid-1980’s
when the Remedial Action Scheme Task Force was formed to review the design of the Pacific
AC Intertie remedial action scheme. This group is now the Remedial Action Scheme Reliability
Subcommittee (RASRS). The individual RASRS members typically are very experienced
people with substantial technical skills in one or more specialties including: protection and
control, telecommunications, transmission planning, design, operations, EMS and dispatch, and
information technology. Collectively the RASRS has extensive experience with designing,
operating and reviewing remedial action schemes. These wide-ranging member skills have
allowed WECC to give the RASRS the responsibility of both review the design and approval all
pertinent RAS within the WECC. The RASRS can aid owners, as needed, to determine whether
a scheme is ―local‖ on a case by case basis.


                                                 3
Two WECC documents pertain specifically to RAS design, operation and the review process.
The ―Remedial Action Scheme Design Guide‖ [2] prepared by the WECC Relay Work Group is
a detailed discussion of the considerations that must be included when designing RAS to assure
that the scheme objectives are met reliably and with ease of operations and maintenance kept
in mind. The ―Information Required to Assess the Reliability of a RAS - Procedure to Submit a
RAS for Assessment‖ [1] is the procedure that WECC and the RASRS use to perform detailed
review of each specific scheme that an owner proposes to place in service. Though these
documents do not directly refer to the NERC standards, the content of the standards that
pertains to the scheme owners is covered. Together these documents also provide substantial
technical guidance for any owner in the design of their schemes.

WECC Proposed Application of the NERC Standards
WECC recently updated its definitions of all three of its RAS classifications, in part to clarify
application of the PRC standards. WECC’s new classification descriptions for Remedial Action
Scheme (RAS), Safety Net and Local Area Protection Scheme (LAPS) are included as
Appendix 1. This document particularly helped clarify differences between ―local‖ schemes
versus ―RAS‖ that have a significant impact outside the local area. The largest ―local area‖ is
generally the Balancing Authority.

Schemes that impact a significant area are what WECC normally refers to as ―RAS‖ and are the
schemes that require detailed review and approval by the RASRS. WECC refers to schemes
that have only local impacts as Local Area Protection Schemes (LAPS). A Safety Net is
intended to remediate the effects of extreme events, such as described by TPL-004-0. While
TPL-004-0 requires that such extreme events be studied, it does not require that they be
remediated, so that Safety Nets are optional under NERC.

If an RRO’s review procedure (established pursuant to PRC-012) determines that a RAS must
be submitted for review and approval, then that RAS must also comply with Standards PRC-013
and PRC-014 (RRO responsibilities) and PRC-015 – PRC-017 (owner responsibilities).
However, if the RRO does not require a RAS to be submitted for review and approval, e.g. a
―local‖ scheme, then that RAS cannot comply with the PRC-013 – PRC-017 requirements.
Such local schemes would still be subject to the requirements of the more general protection
and control standards, generally PRC-001 – PRC-005, though under frequency and under
voltage load shedding standards could also apply, depending on the specific protection system
characteristics. Figure 1 provides a flow diagram for this logic.

Implementation and Coordination Challenges
Neither the ―WECC Remedial Action Scheme Design Guide‖ nor the WECC RAS review
procedure ―Information Required to Assess the Reliability of a RAS - Procedure to Submit a
RAS for Assessment‖ include references to either the PRC-012 – PRC-017 and TPL-001 – TPL-
004 standards or mention the Bulk Electric System. Even without such references, the Design
Guide provides a detailed description of the considerations that a RAS designer should include
in a scheme. The ―Information Required to Assess . . .‖ document provides a detailed outline for
the owner in describing the characteristics of their RAS for the RASRS and aids the RASRS in
reviewing the scheme.

The RAS Design Guide was most recently reviewed and updated in early 2007. Despite the
absence of references to the NERC standards or BES, the Guide’s other significant strengths
lead to the conclusion that an immediate update is not necessary. The normal schedule for
review of this document for possible updates is in 2011-12.


                                                4
The ―Information Required to Assess . . .‖ procedure was most recently reviewed and updated in
2005. While still an excellent RAS review procedure, a few other issues have also appeared
recently. For example, the newly approved RAS classification definitions in Appendix 1 would
be included in a revision. The RASRS expects to fully review and update this document in
conjunction with a larger WECC document categorization project by June 2010. This schedule
will also meet the NERC-specified five-year update schedule for the RROs RAS review
procedure.

The NERC Glossary of Terms defines Bulk Electric System (BES):
      As defined by the Regional Reliability Organization, the electrical generation resources,
      transmission lines, interconnections with neighboring systems, and associated
      equipment, generally operated at voltages of 100 kV or higher. Radial transmission
      facilities serving only load with one transmission source are generally not included in this
      definition.

All NERC standards are intended to apply to the BES. NERC does not (at least yet!) write
standards to govern distribution systems. Though the RAS standards are clearly meant to apply
to a particular type of protection system, known in the WECC as remedial action schemes,
NERC included no direct reference to the BES in standards PRC-012 – PRC-017. The PRC-
012 standard references the TPL standards, which in turn refer to the BES.

WECC has formed the Bulk Electric System Definition Task Force to clarify the NERC definition
of the BES as applied within the Western Interconnection. This Task Force intends that the
resulting clarification will adhere to the Process for Developing and Approving WECC Standards
so that the final product will undergo sufficient due process review.

But perhaps the primary challenge is the need for RAS classifications with enough flexibility to
accommodate future changes without introducing further uncertainties in the applicability of
these Standards.

The FERC notice of proposed rule making (NOPR) issued on October 20, 2006 observed that,
for purposes of section 215 of the FPA, ―Bulk-Power System‖ means:
    (A) facilities and control systems necessary for operating an interconnected electric energy
        transmission network (or any portion thereof) and
    (B) electric energy from generating facilities needed to maintain transmission system
        reliability. The term does not include facilities used in the local distribution of electric
        energy.

FERC’s Order 693 accepted the NERC definition of BES to determine the applicability of the
NERC Reliability Standards, as they are approved by FERC. However, FERC remains
concerned about the need to address the potential for gaps in coverage of facilities, and intends
to address this in a future proceeding.




                                                 5
                                        Neighboring system         Yes
   Start            BES?               impact for inadvertent
                               Yes           operation

                         No                           No

                                           Neighboring             Yes
             No Applicable           system voltage collapse or
            NERC Standard              cascade for Failure to
                                             Operate

                                                     No
                                                                  Yes    RASRS Review,
                                         Scheme on Major
                                         WECC RAS List
                                                                         PRC-013 through
                                                                          PRC-017 apply
                                                      No
                                          Scheme needed
                                          to establish SOL
                                                                    Yes
             RASRS Review not                         No
             Required, PRC-001
           through PRC-005 apply


FIGURE 1. General Logic Flow Diagram to apply the PRC Standards to WECC RAS Review.




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                                                                                                                    TABLE I

                                                                  Regional Reliability Organization Compliance Review Procedures for Remedial Action Schemes

                                                                                          Feedback            Technical
Regional            How to Start the                                                      between             Guidance        Sub-categories of       Triggers for Scheme     Any Particular Focus
Reliability         Review Process     Review & Approval Responsibility                   Reviewers and       from RRO        RAS/SPS?                Review                  or Reference to BES          Specific Requirements
Organization                                                                              Owners              to Owners
WECC (1,2)          Contact RASRS      Remedial Action Scheme Reliability                 Presentation by     Substantial     RAS,                    New or significantly    Focus: None                  Specific review times not stated
                    Chair              Subcommittee review and approval                   owner to RASRS      detail in       Safety Net,             modified                No BES reference
                                                                                                                                                                 th
                                                                                                              both (1,2)      Local Area Protection   Periodic (5 year) by
                                                                                                                              Scheme                  owner
                                                                                                                                                      Removals (not stated)

ERCOT (3,4)         Contact ERCOT      ERCOT staff and affected parties initial review,   Separate Task                       None                    New or modified,        Focus: Use SPS to meet       Fully automatic, Condition monitoring
                                                                                                                                                                 th
                    staff              System Studies TF, Dynamics TF, System             Force reviews,                                              Periodic (5 year)       gen schedule when            for ERCOT Security Operations,
                                       Protection TF questions and comments,              feedback through                                            Removals (not stated)   Xmsn > Plant schedule        Develop SPS exit strategy when
                                       Director ERCOT Operations approves                 ERCOT staff                                                                         (limited ways and time)      possible.
                                                                                                                                                                              No BES reference             Specific schedules to review
                                                                                                                                                                                                           schemes.
MRO (5,6,7)         Initial design     Joint Protective Relay and Transmission            Joint review by                     None                    New or modified,        Focus: None                  Quarterly report by owners of all RAS
                    report to          Assessment Subcommittees special review            team, feedback                                              Periodic (not stated)   Applies to BES within        operations.
                    Reliability        team + Reliability Coordinator. Approve by         with owners at                                              Removals (not stated)   MRO, discuss BES             Specific schedules to review
                    Assessment         Reliability Assessment Committee.                  each level                                                                          impacts from scheme          schemes.
                    Committee (RAC)
NPCC (8,9,10)       Contact Chair of   For Local (Type III) schemes TFCP requests         Each TF may         Substantial     Type I (Inter-Area),    New or modified,        Focus Primarily on Type      Consider relative effects on Bulk
                    Task Force on      review by TF System Protection & TF System         require             detail in (8)   Type II (Extreme        Periodic (not stated)   I. Some criteria don’t       Power System, Type III (local)
                    Coordination of    Studies. TFSP & TFSS review and confirms (or       presentation by                     Contingencies),         Removals (not stated)   apply to Type II. Type III   schemes require less review
                    Planning (TFCP)    denies) local impact. Local schemes are            owner.                              Type III (Local                                 doesn’t require same
                                       approved by TFCP.                                                                      Impact)                                         practices as Type I.         Specific review times not stated
                                       Type I, II schemes reviewed by TFSS, TF                                                                                                Reference to Bulk Power
                                       Coordination of Operations and TFSP and                                                                                                System
                                       recommend to TFCP. TFCP reports to
                                       Reliability Coordinating Committee, which
                                       approves.

Reliability First   Owner submits      SPS review team includes 3 members each            Presentation by                     None                    New or modified,        Focus: None                  Specific schedules to review
                                                                                                                                                                 th
(11)                request to RF      from Transmission Performance and Protection       owner to review                                             Periodic (5 year)       Owner to identify any        schemes.
                    staff              Subcommittees, which conducts technical            team                                                        Removals (simplified    SPS effects on BES
                                       review and reports to Reliability Committee.                                                                   process)                within another Regional
                                                                                                                                                                              Entity

SERC (12,13)        Contact Chair of   DRS review and acceptance                          Data requests,                      None                    New or modified,        Focus: None                  Specific schedules to review
                                                                                                                                                                 th
                    Dynamics Review                                                       questions back to                                           Periodic (5 year)       No BES reference             schemes
                    Subcommittee                                                          owner                                                       Removals (not stated)
                    (DRS)




                                                     7
References
   1) Information Required to Assess the Reliability of a RAS - Procedure to Submit a RAS for
       Assessment,
       http://www.wecc.biz/documents/library/RAS/RAS_Approval_Procedure_04-2005.pdf
   2) WECC Remedial Action Scheme Design Guide,
       http://www.wecc.biz/documents/library/RWG/RAS_Guide_10_clean_02-07-07.pdf
   3) ERCOT, SPS policy – Information Presentation,
       http://search.ercot.com/search?q=sps+policy+presentation&restrict=&btnG=Search+%3
       E&ie=utf8&site=ercot-com&output=xml_no_dtd&client=ercot-
       com&proxystylesheet=http%3A%2F%2Fwww.ercot.com%2Fstyles%2Fgoogle.xslt&getfi
       elds=title.description&oe=utf8
   4) ERCOT ISO SPS or RAP Policy,
       http://search.ercot.com/search?q=sps+policy&btnG=Search+%3E&site=ercot-
       com&client=ercot-
       com&proxystylesheet=http%3A%2F%2Fwww.ercot.com%2Fstyles%2Fgoogle.xslt&outp
       ut=xml_no_dtd&ie=utf8&oe=utf8&getfields=title.description
   5) Midwest Reliability Organization Procedure for Special Protection System Review,
       http://www.midwestreliability.org/04_standards/mro_procedures/nerc_standards/PRC-
       012-0_MRO_SPS_Review_Procedure.pdf
   6) Midwest Reliability Organization Procedure For NERC PRC-012,
       http://www.midwestreliability.org/04_standards/mro_procedures/nerc_standards/PRC-
       012-0_MRO_SPS_Review_S.pdf
   7) Midwest Reliability Organization Procedure For NERC PRC-014,
       http://www.midwestreliability.org/04_standards/mro_procedures/nerc_standards/PRC-
       014-0_MRO_SPS_Assessment.pdf
   8) NPCC, Document A-11, Special Protection System Criteria, http://www.npcc.org
   9) NPCC, Document C-16, Procedure for NPCC Review of New or Modified Bulk Power
       System Special Protection Systems (SPS),
       http://www.npcc.org/documents/regStandards/Procedure.aspx
   10) NPCC Reliability Reference Directory # 7, Special Protection System, November 28,
       2007
   11) ReliabilityFirst, Procedure for the Review of Special Protection Systems (SPS),
       http://www.rfirst.org/Reliability/ReliabilitySpecialProtectionSystems.aspx
   12) SERC Supplement, Special Protection Systems NERC Reliability Standards, PRC-012
       through 017,
       http://www.serc1.org/documents/serc%20supplements/planning/active%20supplements
       %20(wholly%20or%20partially%20reference%20current%20nerc%20reliability%20stand
       ards)/serc%20sps%20supplement%20rev%205%20(10-16-08).pdf
   13) SERC Supplement, Maintenance & Testing – Protection Systems (Transmission,
       Generation, UFLS, UVLS, & SPS),
       http://www.serc1.org/documents/serc%20supplements/planning/active%20supplements
       %20(wholly%20or%20partially%20reference%20current%20nerc%20reliability%20stand
       ards)/maintenance%20and%20testing-
       protection%20systems%20serc%20supplement%20rev%202%20(%20approved%205-
       29-08).pdf




                                              8
                                          APPENDIX 1

                            WECC Guideline:
                  Remedial Action Scheme Classification
                            Date: 02/09/2009
Introduction
WECC classifies Protection Systems required for purposes other than facility protection by the
type of application to determine which NERC Standards apply. The same classifications also
identify whether a particular scheme requires review and approval by the Remedial Action
Scheme Reliability Subcommittee (RASRS).

Guideline
These Protection System classifications identify whether a particular scheme requires review
and approval by the RASRS. They also help the owner and WECC determine which NERC
PRC Standards should apply to the scheme.

The NERC glossary defines a Special Protection System (SPS) or Remedial Action Scheme
(RAS) as:

    An automatic protection system designed to detect abnormal or predetermined system
    conditions, and take corrective actions other than and/or in addition to the isolation of faulted
    components to maintain system reliability. Such action may include changes in demand,
    generation (MW and Mvar), or system configuration to maintain system stability, acceptable
    voltage, or power flows. An SPS does not include (a) underfrequency or undervoltage load
    shedding or (b) fault conditions that must be isolated or (c) out-of-step relaying (not
    designed as an integral part of an SPS). Also called Remedial Action Scheme.

If an owner is not sure whether a Protection System is a RAS under these definitions, the issue
should be discussed with the chair of the RASRS. The chair, or at the chair’s discretion all or
part of the subcommittee, will decide whether further WECC review is needed.

   Remedial Action Scheme (RAS). A RAS Protection System mitigates conditions that could
    violate performance standards or criteria within the systems of multiple owners or Balancing
    Authorities (BAs), even if sensing and action occurs within a single owner or BA’s system. A
    Protection System that mitigates a critical system problem, even when two or more owners
    or Balancing Authorities are involved, may be considered a Local Area Protection Scheme
    at the discretion of the RASRS if the effects of misoperation or failure to operate correctly
    are localized. Any scheme included on the Major WECC RAS List or required to establish
    System Operating Limits (SOLs) is a RAS. A RAS can be needed to meet WECC
    performance criteria or NERC Transmission Planning standards TPL-002-0 Category B
    (single contingency); TPL-003-0 Category C (two or more contingencies); or (draft) TPL-
    001-1, Table 1 and Categories P1–P7. The effects of a scheme failure lead to cascading or
    other performance violations within the Bulk Electric System (BES).

A RAS as described above requires a WECC review by the RASRS. Both RAS owners and
WECC are required to comply with applicable NERC standards:
    NERC PRCs that apply to RROs (WECC): PRC-012, PRC-013, PRC-014



                                                 9
       NERC PRCs that apply to owners: PRC-015, PRC-016, PRC-017

   Safety Net. A Safety Net Protection System protects the Power System from low probability
    or unexpected events that are outside the normal planning criteria, but which may lead to a
    complete system collapse. The scheme operates to minimize the severity of the event and
    attempts to prevent a system collapse or cascading outages. A safety net is typically
    intended to handle the more severe disturbances resulting from extreme, though perhaps
    not well-defined, events. Due to the difficulty in defining the series (or sequences) of credible
    outages or possible misoperations of protection systems, or in predicting conditions such as
    total failure of conventional protection systems in a particular area under study; safety net
    schemes may not involve planning studies at the same level of detail as for other forms of
    similar Protection Systems; i.e, condition-based schemes. Redundancy is not necessarily
    required for safety net scheme design. The effects of a safety net’s failure to operate as
    designed are separately limited by the actions of the independent Protection Systems or
    RAS of which it is composed. Unintended safety net operation may have significant adverse
    impact either within the particular owner’s system or in some cases outside the immediate
    system’s area.

A safety net defends against extensive cascading or system collapse resulting from severe
unforeseen contingencies, as described in NERC Transmission Planning standards TPL-004-0,
Category D (multiple contingencies) or (draft) TPL-001-1 Table 1, Extreme Events. A safety net
is not used to establish SOLs. The TPL standards require that specified Multiple Contingencies /
Extreme Events be studied, but do not require that such events be mitigated.

A safety net localizes disturbances by minimizing cascading and uncontrolled loss of
generation, transmission, and interruption of customer electric service. Portions of a safety net
may include a RAS to remediate other, more likely disturbances that could otherwise escalate
into a more severe disturbance.

A safety net is subject to review by the WECC RASRS if unintended operation would result in
cascading or other performance standard violations. A safety net may also be reviewed upon
request of the owner, the WECC Operating Practices Subcommittee (OPS), or other appropriate
entity; e.g., following a scheme misoperation. The RASRS reviews a safety net in a manner
similar to a RAS. Since a safety net goes beyond the mitigation intent of the TPL standards,
RASRS reviews of safety nets are intended for information, comment, and feedback rather than
approval. However, to the extent possible, safety net reviews by the RASRS are generally
guided by the standards that apply to RAS.

   Local Area Protection Scheme (LAPS). A LAPS is a Protection System that meets system
    performance standards and criteria within one or more owner's system(s). If more than one
    owner is affected, all owners must agree to be bound by the effects of the LAPS; e.g.,
    through interconnection agreements. All sensing and mitigation must occur within the
    agreeing owners’ system(s). The effects of scheme failure are limited to the agreeing
    owners’ system(s). Normally all affected owners must be within a single Balancing Authority.
    As noted above, a Protection System that mitigates a critical system problem even when two
    or more owner’s or Balancing Authorities are involved, may be considered a Local Area
    Protection Scheme at the discretion of the RASRS, if the effects of misoperation or failure to
    operate correctly are localized.




                                                 10
A Local Area Protection Scheme does not require a WECC RASRS review. However, such a
scheme may be reviewed by the RASRS upon request of the owner, the WECC OPS, or other
appropriate entity; e.g., following a scheme misoperation. It is recognized that future system
changes can require that a scheme — initially needed only for local area protection — be re-
classified as a RAS and be reviewed and approved by the RASRS.

WECC considers Local Area Protection Schemes as Protection Systems under the NERC
Glossary definitions (not RAS or SPS). LAPS are therefore required to comply with the more
general Protection System, rather than Special Protection System (RAS) PRC standards. It is
the responsibility of the owner to determine which specific standards apply to their scheme.
WECC does not document the owner’s compliance of LAPS with these standards.
     NERC PRCs that generally apply to RROs (WECC): PRC-002, PRC-003
     NERC PRCs that generally apply to owners: PRC-001, PRC-004, PRC-005

Effective Period
This document will remain in effect until incorporated into the next revision of the RASRS
Guideline ―Information Required to Assess the Reliability of a RAS / Procedure to Submit a RAS
for Assessment.‖ When such a revision is approved, this document will be retired.


Approved By:
         Approving Committee, Entity or Person                        Date
    Remedial Action Scheme Reliability Subcommittee
                  Operating Committee




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