RAS Type Definitions by wxr16887

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									                               WECC Guideline:
                     Remedial Action Scheme Classification
                                           Date: 05/09/2009

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Document Publication Date:          5/09/2009
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                         WECC Guideline:
               Remedial Action Scheme Classification
                         Date: 05/09/2009
Introduction
WECC classifies Protection Systems required for purposes other than facility protection
by the type of application to determine which NERC Standards will fulfill WECC’s
responsibilities. 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 fulfill WECC’s responsibilities.

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 that requires further
WECC review 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 2) TPL-001-1, Table 1 and Categories P1–P7. The effects


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of a scheme failure lead to cascading or other performance violations within the Bulk
Electric System (BES).

A RAS as described above requires WECC review by the RASRS. Data should be
provided as described in the “Information Required to Assess the Reliability of a RAS /
Procedure to Submit a RAS for Assessment.” These schemes are included in the
WECC RAS database. Owners will maintain the same RAS data in their own database.

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
    NERC PRCs that NERC applies to owners and providers: 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 2) 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, using data as described in the


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“Information Required to Assess. . .” procedure. Since a safety net goes beyond the
mitigation intent of the TPL standards, RASRS reviews of safety nets are primarily
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 and are included in the WECC RAS database. Owners will maintain
information on all their safety nets in their own database.

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 need to be within a single
Balancing Authority. As noted above, 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.

A Local Area Protection Scheme does not require a WECC RASRS review and
approval. 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 since scheme failure would not violate WECC performance
criteria. LAPS are therefore required to comply with the more general Protection
System standards for the purpose of WECC review. It is the responsibility of the owner
to determine which specific standards apply to their scheme. LAPS are included in the
owner’s data base but not in the WECC database, except at WECC’s option as
described in the immediately preceding paragraph.
      NERC PRCs that generally apply to RROs (WECC): PRC-002, PRC-003, PRC-
         012, PRC-013, PRC-014
      NERC PRCs that WECC generally applies to owners: PRC-001, PRC-004, PRC-
         005
      NERC PRCs that NERC may apply to owners: PRC-015, PRC-016, PRC-017

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


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Remedial Action Scheme Reliability Subcommittee
             Operating Committee




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