preparer: prabhu gnanam

PREPARER: Prabhu Gnanam

WITNESS: ERCOT has not yet designated any witnesses.

50

50

1-29. On February 17, 2014, Calpine filed with ERCOT Supplemental Comments thatquestioned ERCOT's 2010-2020 load growth assumptions for ERCOT, Houston LoadZone, the North Central Zone and Southern Zone because the assumptions varied widelyfrom actual zone growth rates for the period 2003-2013. ERCOT's response stated, inpart, "ERCOT concludes that Calpine's assertion 'if the relative growth rate for Houstonand the South weather zone is lower or on par with that of North Central, the need foradditional import capability into Houston, under the same G-l+N-1 reliabilityrequirement, would have disappeared' is not supported based on the reliability andsensitivity studies that ERCOT has performed for the this review." Please provide thereliability and sensitivity studies referenced in ERCOT's response.

Response:

The reliability and sensitivity studies were provided in section 4 (Project Need) of the HIPreport. The cases used for the studies include the 2018 HIP study base case and threesensitivity cases with and without varying load and generation in 2018 SSWG case. Thesestudies were based on the load forecasted for the year 2018 and historical data. As shown inthe result of the studies, the reliability issue is driven by serving the projected load in theHouston area using the available resources in the ERCOT system. Therefore, the relativegrowth rates asserted by Calpine would not provide any impact on the reliability need.

Please provide analysis results that show how the need for North - Houston transfercapability will change, if load in the Coast, North Central and Southern weather zonesgrows at a similar rate from 2010 to 2018 (i.e., start from theIODSA_2010_SUMI_Final04162010 SSWG case, and then grow the load through 2018at a same rate for these zones). Also, please provide analysis to confirm, using a uniform1.30% growth rate for all weather zones, whether the need for additional import willcompletely disappear. If not, please confirm how much additional import capability isneeded.

Response:

ERCOT has objected to this portion of the request.

PREPARER: Prabhu Gnanam and Patrick Peters


51

51

1-30. Confirm or deny that ERCOT's "90th Percentile Summer Non-Coincident Peak byWeather Zone" load forecast, posted at the following link,http://www.ercot.com/gridinfo/load/forecast/index.html, indicates a 5.6% increase in loadbetween 2014 and 2018 for the North Central weather zone. If denied, what is theforecasted load increase?

Response:

Confirmed. -5.56%



52

52

1-31. Confirm or deny that ERCOT's "90th Percentile Summer Non-Coincident Peak byWeather Zone" load forecast, posted at the following link,http://www.ercot.com/gridinfo/load/forecast/index.html, indicates a 4.2% increase in loadbetween 2014 and 2018 for the Coastal weather zone. If denied, what is the forecastedload increase?

Response:

Confirmed. -4.22%



53

53

1-32. Confirm or deny that the SSWG Forecast on page 7 of the 2013 Regional TransmissionPlan Report dated December 30, 2013 indicates a 6.0% increase in load between 2014and 2018 for the North Central weather zone. If denied, what is the forecasted loadincrease?

Response:

Confirmed. -5.97%



54

54

1-33. Confirm or deny that the SSWG Forecast on page 7 of the 2013 Regional TransmissionPlan Report dated December 30, 2013 indicates a 7.6% increase in load between 2014and 2018 for the Coastal weather zone. If denied, what is the forecasted load increase?

Response:

Confirmed. -7.64%



55

55

1-7-c-i

Standard TPL-001-0.1 - System Performance Under Normal Conditions

A. Introduction

1. Title: System Performance Under Normal (No Contingency) Conditions (Category A)

2. Number: TPL-001-0.1

3. Purpose: System simulations and associated assessments are needed periodically toensure that reliable systems are developed that meet specified performancerequirements with sufficient lead time, and continue to be modified or upgraded asnecessary to meet present and future system needs.

4. Applicability:

4.1. Planning Authority

4.2. Transmission Planner

5. Effective Date: May 13, 2009

B. Requirements

R1. The Planning Authority and Transmission Planner shall each demonstrate through avalid assessment that its portion of the interconnected transmission system is plannedsuch that, with all transmission facilities in service and with normal (pre-contingency)operating procedures in effect, the Network can be operated to supply projectedcustomer demands and projected Firm (non- recallable reserved) TransmissionServices at all Demand levels over the range of forecast system demands, under theconditions defined in Category A of Table I. To be considered valid, the PlanningAuthority and Transmission Planner assessments shall:

R1.1. Be made annually.

R1.2. Be conducted for near-term (years one through five) and longer-term (years sixthrough ten) planning horizons.

R1.3. Be supported by a current or past study and/or system simulation testing thataddresses each of the following categories, showing system performancefollowing Category A of Table 1(no contingencies). The specific elementsselected (from each of the following categories) shall be acceptable to theassociated Regional Reliability Organization(s).

R1.3.1. Cover critical system conditions and study years as deemedappropriate by the entity performing the study.

R1.3.2. Be conducted annually unless changes to system conditions do notwarrant such analyses.

R1.3.3. Be conducted beyond the five-year horizon only as needed to addressidentified marginal conditions that may have longer lead-timesolutions.

R1.3.4. Have established normal (pre-contingency) operating procedures inplace.

R1.3.5. Have all projected firm transfers modeled.

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56


R1.3.6. Be performed for selected demand levels over the range of forecastsystem demands.

R1.3.7. Demonstrate that system performance meets Table I for Category A(no contingencies).

R1.3.8. Include existing and planned facilities.

R1.3.9. Include Reactive Power resources to ensure that adequate reactiveresources are available to meet system performance.

R1.4. Address any planned upgrades needed to meet the performance requirementsof Category A.

R2. When system simulations indicate an inability of the systems to respond as prescribedin Reliability Standard TPL-001-0_R1, the Planning Authority and TransmissionPlanner shall each:

R2.1. Provide a written summary of its plans to achieve the required systemperformance as described above throughout the planning horizon.

R2.1.1. Including a schedule for implementation.

R2.1.2. Including a discussion of expected required in-service dates offacilities.

R2.1.3. Consider lead times necessary to implement plans.

R2.2. Review, in subsequent annual assessments, (where sufficient lead time exists),the continuing need for identified system facilities. Detailed implementationplans are not needed.

R3. The Planning Authority and Transmission Planner shall each document the results ofthese reliability assessments and corrective plans and shall annually provide these to itsrespective NERC Regional Reliability Organization(s), as required by the RegionalReliability Organization.

C. Measures

M1. The Planning Authority and Transmission Planner shall have a valid assessment andcorrective plans as specified in Reliability Standard TPL-001-0R I and TPL-001-0R2. -

M2. The Planning Authority and Transmission Planner shall have evidence it reporteddocumentation of results of its Reliability Assessments and corrective plans perReliability Standard TPL-001-0 R3.

D. Compliance

1. Compliance Monitoring Process

1.1. Compliance Monitoring ResponsibilityCompliance Monitor: Regional Reliability Organization.

Each Compliance Monitor shall report compliance and violations to NERC via the NERCCompliance Reporting Process.

1.2. Compliance Monitoring Period and Reset Time Frame

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57


Annually

1.3. Data RetentionNone specified.

1.4. Additional Compliance Information

2. Levels of Non-Compliance

2.1. Level 1: Not applicable.

2.2. Level 2: A valid assessment and corrective plan for the longer-term planninghorizon is not available.


2.4. Level 4: A valid assessment and corrective plan for the near-term planninghorizon is not available.

E. Regional Differences

1. None identified.

Version History

Version Date Action Change Tracking0 April 1, 2005 Effective Date New

0 February 8, 2005 BOT Approval Revised

0 June 3, 2005 Fixed reference in Ml to read TPL-001-0 R2.1

and TPL-001-0 R2.2Errata

0 July 24, 2007 Corrected reference in M1. to read TPL-001-0

RI and TPL-001-0 R2.Errata

0.1 October 29, 2008 BOT adopted errata changes; updated versionnumber to "0.1"

Errata

0.1 May 13, 2009 FERC Approved - Updated Effective Date Revised

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58


Table I. Transmission System Standards - Normal and Emergency Conditions

CategoryContingencies System Limits or Im pacts

SystemStable and

both Thermal Loss of

Initiating Event(s) and Contingency and Voltage Demand or Cascading

Element(s) Limits within Curtailed Firm OutagesApplicable Transfers

Rating a

A All Facilities in Service Yes No NoNo Contingencies

Single Line Ground (SLG) or 3-Phase (30)B Fault, with Normal Clearing, Yes No b No

Event resulting in 1 Generator Yes No b Nothe loss of a single 2 Transmission Circuit Yes No b Noelement 3. Transformer Yes Nob

NoLoss of an Element without a Fault

Single Pole Block, Normal Clearinge4. Single Pole (dc) Line Yes Nob

No

SLG Fault, with Normal ClearingeC

Event(s) resultingI Bus Section Yes Planned/

`No

in the loss of two2 Breaker (failure or internal Fault) Yes

ControlledPlanned/ Noor more (multiple)

Controlled`elements

SLG or 30 Fault, with Normal Clearing e,Manual System Adjustments, followed byanother SLG or 30 Fault, with Normal

Clearinge Yes Planned/ No

3 Category B (B l, B2, B3, or B4)Controlled°

contingency, manual systemadjustments, followed by anotherCategory B (B 1, B2, B3, or B4)contingency

Bipolar Block, with Normal Clearinge4 Bipolar (dc) Line Fault (non 30), with Planned/

Normal Clearmge. Yes Controlled° No

5 Any two circuits of a multiple circuitf

Yes Planned/ Ntowerlme oControlled`

SLG Fault, with Delayed Clearinge (stuckbreaker or protection system failure)

6 Generator Yes Planned/ NoControlled°

7 Transformer Yes Planned/ NoControlled`

8 Transmission Circuit Yes Planned/ NoControlled°

9 Bus Section Yes Planned/ NoControlled`

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59


D° 30 Fault, with Delayed Clearing e(stuck breaker or protection system Evaluate for risks and

Extreme event resulting infailure) consequences

two or more (multiple) I Generator 3 Transformer • May involve substantial loss ofelements removed orCascading out of service 2 Transmission Circuit 4 Bus Section

customer Demand andgeneration in a widespread

_. ___ .... _ ^.._t area or areas.__..R ^. _.^.^.^..„.n Portions or all of the

30 Fault, with Normal Clearinge interconnected systems mayor may not achieve a new,

5 Breaker (failure or internal Fault) stable operating point,• Evaluation of these events may

6. Loss of towerline with three or more circuits require joint studies with

7. All transmission lines on a common right-of wayneighboring systems

8 Loss of a substation (one voltage level plus transformers)

9 Loss of a switching station (one voltage level plustransformers)

10 Loss of all generating units at a station

11 Loss of a large Load or major Load center

12. Failure of a fully redundant Special Protection System (orremedial action scheme) to operate when required

13 Operation, partial operation, or misoperation of a fullyredundant Special Protection System (or Remedial ActionScheme) in response to an event or abnormal systemcondition for which it was not intended to operate

14 Impact of severe power swings or oscillations fromDisturbances in another Regional Reliability Organization

a) Applicable rating refers to the applicable Normal and Emergency facility thermal Rating or system voltage limitas determined and consistently applied by the system or facility owner. Applicable Ratings may includeEmergency Ratings applicable for short durations as required to permit operating steps necessary to maintainsystem control. All Ratings must be established consistent with applicable NERC Reliability Standardsaddressing Facility Ratings.

b) Planned or controlled interruption of electric supply to radial customers or some local Network customers,connected to or supplied by the Faulted element or by the affected area, may occur in certain areas withoutimpacting the overall reliability of the interconnected transmission systems. To prepare for the nextcontingency, system adjustments are permitted, including curtailments of contracted Firm (non-recallablereserved) electric power Transfers.

c) Depending on system design and expected system impacts, the controlled interruption of electric supply tocustomers (load shedding), the planned removal from service of certain generators, and/or the curtailment ofcontracted Firm (non-recallable reserved) electric power Transfers may be necessary to maintain the overallreliability of the interconnected transmission systems.

d) A number of extreme contingencies that are listed under Category D and judged to be critical by thetransmission planning entity(ies) will be selected for evaluation. It is not expected that all possible facilityoutages under each listed contingency of Category D will be evaluated.

e) Normal clearing is when the protection system operates as designed and the Fault is cleared in the timenormally expected with proper functioning of the installed protection systems. Delayed clearing of a Fault isdue to failure of any protection system component such as a relay, circuit breaker, or current transformer, andnot because of an intentional design delay.

f) System assessments may exclude these events where multiple circuit towers are used over short distances (e.g.,station entrance, river crossings) in accordance with Regional exemption criteria.

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60

Standard TPL-002-Ob - System Performance Following Loss of a Single BES Element

A. Introduction

1. Title: System Performance Following Loss of a Single Bulk Electric SystemElement (Category B)

2. Number: TPL-002-Ob

3. Purpose: System simulations and associated assessments are needed periodically to ensurethat reliable systems are developed that meet specified performance requirementswith sufficient lead time, and continue to be modified or upgraded as necessaryto meet present and future system needs.

4. Applicability:



5. Effective Date: Immediately after approval of applicable regulatory authorities.B. Requirements

R1. The Planning Authority and Transmission Planner shall each demonstrate through a validassessment that its portion of the interconnected transmission system is planned such that theNetwork can be operated to supply projected customer demands and projected Firm (non-recallable reserved) Transmission Services, at all demand levels over the range of forecastsystem demands, under the contingency conditions as defined in Category B of Table I. To bevalid, the Planning Authority and Transmission Planner assessments shall:



R1.3. Be supported by a current or past study and/or system simulation testing thataddresses each of the following categories,, showing system performance followingCategory B of Table 1(single contingencies). The specific elements selected (fromeach of the following categories) for inclusion in these studies and simulations shallbe acceptable to the associated Regional Reliability Organization(s).

R1.3.1. Be performed and evaluated only for those Category B contingencies thatwould produce the more severe System results or impacts. The rationale forthe contingencies selected for evaluation shall be available as supportinginformation. An explanation of why the remaining simulations wouldproduce less severe system results shall be available as supportinginformation.

R1.3.2. Cover critical system conditions and study years as deemed appropriate bythe responsible entity.

R1.3.3. Be conducted annually unless changes to system conditions do not warrantsuch analyses.

R1.3.4. Be conducted beyond the five-year horizon only as needed to addressidentified marginal conditions that may have longer lead-time solutions.


R1.3.6. Be performed and evaluated for selected demand levels over the range offorecast system Demands.

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61

Standard TPL-002-Ob - System Performance Following Loss ofa Single BES Element

R1.3.7. Demonstrate that system performance meets Category B contingencies.


R1.3.9. Include Reactive Power resources to ensure that adequate reactive resourcesare available to meet system performance.

111.3.10. Include the effects of existing and planned protection systems, including anybackup or redundant systems.

R1.3.11. Include the effects of existing and planned control devices.

R1.3.12. Include the planned (including maintenance) outage of any bulk electricequipment (including protection systems or their components) at thosedemand levels for which planned (including maintenance) outages areperformed.

R1.4. Address any planned upgrades needed to meet the performance requirements ofCategory B of Table I.

R1.5. Consider all contingencies applicable to Category B.

R2. When System simulations indicate an inability of the systems to respond as prescribed inReliability Standard TPL-002-0_Rl, the Planning Authority and Transmission Planner shalleach:

R2.1. Provide a written summary of its plans to achieve the required system performance asdescribed above throughout the planning horizon:


R2.1.2. Including a discussion of expected required in-service dates of facilities.


R2.2. Review, in subsequent annual assessments, (where sufficient lead time exists), thecontinuing need for identified system facilities. Detailed implementation plans are notneeded.

R3. The Planning Authority and Transmission Planner shall each document the results of itsReliability Assessments and corrective plans and shall annually provide the results to itsrespective Regional Reliability Organization(s), as required by the Regional ReliabilityOrganization.

C. Measures

M1. The Planning Authority and Transmission Planner shall have a valid assessment and correctiveplans as specified in Reliability Standard TPL-002-0_Ri and TPL-002-0_R2.

M2. The Planning Authority and Transmission Planner shall have evidence it reporteddocumentation of results of its reliability assessments and corrective plans per ReliabilityStandard TPL-002-0 R3.

D. Compliance

Compliance Monitoring Process

1.1. Compliance Monitoring Responsibility

Compliance Monitor: Regional Reliability Organizations.Each Compliance Monitor shall report compliance and violations to NERC via the NERCCompliance Reporting Process.

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62


1.2. Compliance Monitoring Period and Reset Timeframe

Annually.

1.3. Data Retention

None specified.


None.



2.2. Level 2: A valid assessment and corrective plan for the longer-term planning horizon isnot available.


2.4. Level 4: A valid assessment and corrective plan for the near-term planning horizon is notavailable.


1. None identified.

Version History

Version Date Action Change Tracking0 February 8, Adopted by NERC Board of Trustees New

2005

0 April 1, 2005 Effective Date NewOa July 30, 2008 Adopted by NERC Board of Trustees NewOa October 23, Added Appendix 1- Interpretation of TPL- Revised

2008 002-0 Requirements R1.3.2 and R1.3.12and TPL-003-0 Requirements R1.3.2 andR1.3.12 for Ameren and MISO

Ob November 5, Added Appendix 2 - Interpretation of Interpretation2009 R1.3.10 approved by BOT on November 5,

2009

Ob September 15, FERC Order issued approving the Interpretation2011 Interpretation of R1.3.10 (FERC Order

becomes effective October 24, 2011)

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63



Catego ry Contingencies System Limits or Imp actsSystem Stable

and bothThermal and Loss of Demand

Initiating Event(s) and Contin enc Voltage or Cascadingg yElement(s) Limits within Curtailed Firm Outages

Applicable TransfersRating a


Single Line Ground (SLG) or 3-Phase (30) Fault,B with Normal Clearing Yes No b NoEvent resulting in I Generator Yes No b Nthe loss of a single 2. Transmission Circuit Yes No b

oNoelement 3 Transformer Yes No b NoLoss of an Element without a Fault

Single Pole Block, Normal Clearinge4 Single Pole (dc) Line Yes Nob No

SLG Fault, with Normal Clearinge.C

Event(s) resulting in I Bus Section Yes Planned/ No

the loss of two or Controlled`

more (multiple)2 Breaker (failure or internal Fault) Yes Planned/ No

l Controlled`e ementsSLG or 30 Fault, with Normal Clearinge, ManualSystem Adjustments, followed by another SLG or

30 Fault, with Normal Clearmge3 Category B (B 1, B2, B3, or B4)

Yes Planned/ No

contingency, manual system adjustments Controlled°,

followed by another Category B (B 1, B2,B3, or B4) contingency


Normal Clearinge Yes Controlled° No

5 Any two circuits of a multiple circuitYtowerlmer es Planned/ No

Controlled°SLG Fault, with Delayed Clearinge (stuck breakeror protection system failure)

6 Generator Yes Planned/ NoControlled`

7 Transformer Yes Planned/ NoControlled°

8 Transmission Circuit Yes Planned/ NoControlled`

9 Bus Section Yes Planned/ NoControlled`

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64


D a 30 Fault, with Delayed Clearmge (stuck breaker or protection system Evaluate for risks and

Extreme event resulting infailure) consequences.

two or more (multiple)elements removed or

1 Generator 3. Transformer • May involve substantial loss of

Cascading out of service 2 Transmission Circuit 4 Bus Section------

customer Demand andgeneration in a widespread

--------------e-------------------------30 Fault, with Normal Clearing

area or areas• Portions or all of the

5 Breaker (failure or internal Fault) interconnected systems mayor may not achieve a new,

6 Loss of towerline with three or more circuitsstable operating point

n Evaluation of these events may7 All transmission lines on a common right-ofway require joint studies with8 Loss of a substation (one voltage level plus transformers) neighboring systems.

9 Loss of a switching station (one voltage level plus transformers)10 Loss of all generating units at a station


12 Failure of a fully redundant Special Protection System (orremedial action scheme) to operate when required

13 Operation, partial operation, or misoperation of a fully redundantSpecial Protection System (or Remedial Action Scheme) inresponse to an event or abnormal system condition for which itwas not intended to operate

14 Impact of severe power swings or oscillations from Disturbancesin another Regional RPhah-ht,,

a) Applicable rating refers to the applicable Normal and Emergency facility thermal Rating or system voltage limit asdetermined and consistently applied by the system or facility owner. Applicable Ratings may include Emergency Ratingsapplicable for short durations as required to permit operating steps necessary to maintain system control. All Ratingsmust be established consistent with applicable NERC Reliability Standards addressing Facility Ratings.

b) Planned or controlled interruption of electric supply to radial customers or some, local Network customers, connected to orsupplied by the Faulted element or by the affected area, may occur in certain areas without impacting the overallreliability of the interconnected transmission systems. To prepare for the next contingency, system adjustments arepermitted, including curtailments of contracted Firm (non-recallable reserved) electric power Transfers.

c) Depending on system design and expected system impacts, the controlled interruption of electric supply to customers(load shedding), the planned removal from service of certain generators, and/or the curtailment of contracted Firm (non-recallable reserved) electric power Transfers may be necessary to maintain the overall reliability of the interconnectedtransmission systems.

d) A number of extreme contingencies that are listed under Category D and judged to be critical by the transmissionplanning entity(ies) will be selected for evaluation. It is not expected that all possible facility outages under each listedcontingency of Category D will be evaluated.

e) Normal clearing is when the protection system operates as designed and the Fault is cleared in the time normally expectedwith proper functioning of the installed protection systems. Delayed clearing of a Fault is due to failure of any protectionsystem component such as a relay, circuit breaker, or current transformer, and not because of an intentional design delay.

f) System assessments may exclude these events where multiple circuit towers are used over short distances (e.g., stationentrance, river crossings) in accordance with Regional exemption criteria.

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65


Appendix 1

Interpretation of TPL-002-0 Requirements R1.3.2 and R1.3.12 andTPL-003-0 Requirements R1.3.2 and R1.3.12 for Ameren and MISO

NERC received two requests for interpretation of identical requirements (Requirements R1.3.2 andR1.3.12) in TPL-002-0 and TPL-003-0 from the Midwest ISO and Ameren. These requirements state:

TPL-002-0:

[To be valid, the Planning Authority and Transmission Planner assessments shall:]R1.3 Be supported by a current or past study and/or system simulation testing that addresses each

of the following categories, showing system performance following Category B of Table 1(single contingencies). The specific elements selected (from each of the following categories)for inclusion in these studies and simulations shall be acceptable to the associated RegionalReliability Organization(s).

R1.3.2 Cover critical system conditions and study years as deemed appropriate by theresponsible entity.

R9.3.12 Include the planned (including maintenance) outage of any bulk electric equipment(including protection systems or their components) at those demand levels for whichplanned (including maintenance) outages are performed.

TPL-003-0:


of the following categories, showing system performance following Category C of Table 1(multiple contingencies). The specific elements selected (from each of the followingcategories) for inclusion in these studies and simulations shall be acceptable to the associatedRegional Reliability Organization(s).



Requirement R1.3.2

Request for Interpretation of TPL-002-0 and TPL-003-0 Requirement R1.3.2Received from Ameren on July 25, 2007:Ameren specifically requests clarification on the phrase, `critical system conditions' in R1.3.2. Ameren

asks if compliance with R1.3.2 requires multiple contingent generating unit Outages as part of possiblegeneration dispatch scenarios describing critical system conditions for which the system shall be plannedand modeled in accordance with the contingency definitions included in Table 1.

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Request for Interpretation of TPL-002-0 and TPL-003-0 Requirement R1.3.2Received from MISO on August 9, 2007:MISO asks if the TPL standards require that any specific dispatch be applied, other than one that isrepresentative ofsupply offirm demand and transmission service commitments, in the modeling ofsystemcontingencies specified in Table 1 in the TPL standards.

MISO then asks if a variety ofpossible dispatch patterns should be included in planning analysesincluding a probabilistically based dispatch that is representative ofgeneration deficiency scenarios,would it be an appropriate application of the TPL standard to apply the transmission contingencyconditions in Category B of Table 1 to these possible dispatch pattern.

The following interpretation of TPL-002-0 and TPL-003-0 Requirement R1.3.2 was developed bythe NERC Planning Committee on March 13, 2008:

The selection of a credible generation dispatch for the modeling of critical system conditions is within thediscretion of the Planning Authority. The Planning Authority was renamed "Planning Coordinator" (PC)in the Functional Model dated February 13, 2007. (TPL -002 and -003 use the former "PlanningAuthority" name, and the Functional Model terminology was a change in name only and did not affectresponsibilities.)

- Under the Functional Model, the Planning Coordinator "Provides and informs Resource Planners,Transmission Planners, and adjacent Planning Coordinators of the methodologies and tools for thesimulation of the transmission system" while the Transmission Planner "Receives from the PlanningCoordinator methodologies and tools for the analysis and development of transmission expansionplans." A PC's selection of "critical system conditions" and its associated generation dispatch fallswithin the purview of "methodology."

Furthermore, consistent with this interpretation, a Planning Coordinator would formulate critical systemconditions that may involve a range of critical generator unit outages as part of the possible generatordispatch scenarios.

Both TPL-002-0 and TPL-003-0 have a similar measure M1:

Ml. The Planning Authority and Transmission Planner shall have a valid assessment andcorrective plans as specified in Reliability Standard TPL-002-0_R1 [or TPL-003-0 R1]and TPL-002-0-R2 [or TPL-003-0_R2]." -

The Regional Reliability Organization (RRO) is named as the Compliance Monitor in both standards.Pursuant to Federal Energy Regulatory Commission (FERC) Order 693, FERC eliminated the RRO as theappropriate Compliance Monitor for standards and replaced it with the Regional Entity (RE). Seeparagraph 157 of Order 693. Although the referenced TPL standards still include the reference to theRRO, to be consistent with Order 693, the RRO is replaced by the RE as the Compliance Monitor for thisinterpretation. As the Compliance Monitor, the RE determines what a "valid assessment" means whenevaluating studies based upon specific sub-requirements in R1.3 selected by the Planning Coordinator andthe Transmission Planner. If a PC has Transmission Planners in more than one region, the REs mustcoordinate among themselves on compliance matters.

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Standard TPL-002-Ob - System Performance Following Loss of a SinRle BES Element

Requirement R1.3.12

Request for Interpretation of TPL-002-0 and TPL-003-0 Requirement R1.3.12Received from Ameren on July 25, 2007:Ameren also asks how the inclusion of planned outages should be interpreted with respect to thecontingency definitions specified in Table 1 for Categories B and C. Specifically, Ameren asks if R1.3.12requires that the system be planned to be operated during those conditions associated with plannedoutages consistent with the performance requirements described in Table 1 plus any unidentified outage.

Request for Interpretation of TPL-002-0 and TPL-003-0 Requirement R1.3.12Received from MISO on August 9, 2007:MISO asks if the term "planned outages " means only already known/scheduled planned outages that maycontinue into the planning horizon, or does it include potential planned outages not yet scheduled thatmay occur at those demand levels for which planned (including maintenance) outages are performed?

If the requirement does include not yet scheduled but potential planned outages that could occur in theplanning horizon, is the following a proper interpretation of this provision?

The system is adequately planned and in accordance with the standard if, in order for a system operatorto potentially schedule such a planned outage on the future planned system, planning studies show that asystem adjustment (load shed, re-dispatch ofgenerating units in the interconnection, or system

reconfiguration) would be required concurrent with taking such a planned outage in order to prepare fora Category B contingency (single element forced out of service)? In other words, should the system ineffect be planned to be operated as for a Category C3 n-2 event, even though the first event is a plannedbase condition?

If the requirement is intended to mean only known and scheduled planned outages that will occur or maycontinue into the planning horizon, is this interpretation consistent with the original interpretation byNERC of the standard as provided by NERC in response to industry questions in the Phase I developmentof this standardl ?


This provision was not previously interpreted by NERC since its approval by FERC and other regulatoryauthorities. TPL-002-0 and TPL-003-0 explicitly provide that the inclusion of planned (includingmaintenance) outages of any bulk electric equipment at demand levels for which the planned outages arerequired. For studies that include planned outages, compliance with the contingency assessment for TPL-002-0 and TPL-003-0 as outlined in Table 1 would include any necessary system adjustments whichmight be required to accommodate planned outages since a planned outage is not a "contingency" asdefined in the NERC Glossary of Terms Used in Standards.

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Appendix 2

Requirement Number and Text of Requirement

R1.3. Be supported by a current or past study and/or system simulation testing that addresses each of thefollowing categories, showing system performance following Category B of Table 1 (singlecontingencies). The specific elements selected (from each of the following categories) for inclusion inthese studies and simulations shall be acceptable to the associated Regional Reliability Organization(s).

R1.3.10. Include the effects of existing and planned protection systems, including any backup orredundant systems.

Background Information for Interpretation

Requirement R1.3 and sub-requirement R1.3.10 of standard TPL-002-Oa contain three key obligations:1. That the assessment is supported by "study and/or system simulation testing that addresses each

the following categories, showing system performance following Category B of Table 1(single"contingencies).

2. "...these studies and simulations shall be acceptable to the associated Regional ReliabilityOrganization(s)."

3. "Include the effects of existing and planned protection systems, including any backup orredundant systems."

Category B of Table 1(single Contingencies) specifies:Single Line Ground (SLG) or 3-Phase (30) Fault, with Normal Clearing:

1. Generator

2. Transmission Circuit

3. Transformer

Loss of an Element without a Fault.

Single Pole Block, Normal Clearinge:4. Single Pole (dc) Line

Note e specifies:

e) Normal Clearing is when the protection system operates as designed and the Fault is cleared in the timenormally expected with proper functioning of the installed protection systems. Delayed clearing of a Faultis due to failure of any protection system component such as a relay, circuit breaker or current,transformer, and not because of an intentional design delay.The NERC Glossary of Terms defines Normal Clearing as "A protection system operates as designed andthe fault is cleared in the time normally expected with ro er f ti i fp p unc on ng o the installed protectionsystems."

Conclusion

TPL-002-Oa requires that System studies or simulations be made to assess the impact of singleContingency operation with Normal Clearing. TPL-002-Oa R1.3.10 does require that all elementsexpected to be removed from service through normal operations of the Protection Systems be removed insimulations.

This standard does not require an assessment of the Transmission System performance due to a ProtectionSystem failure or Protection System misoperation. Protection System failure or Protection Systemmisoperation is addressed in TPL-003-0 - System Performance following Loss of Two or More Bulk

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Electric System Elements (Category C) and TPL-004-0 - System Performance Following ExtremeEvents Resulting in the Loss of Two or More Bulk Electric System Elements (Category D).

TPL-002-Oa R1.3.10 does not require simulating anything other than Normal Clearing when assessing theimpact of a Single Line Ground (SLG) or 3-Phase (30) Fault on the performance of the TransmissionSystem.

In regards to PacifiCorp's comments on the material impact associated with this interpretation, theinterpretation team has the following comment:

Requirement R2.1 requires "a written summary of plans to achieve the required system performance,"including a schedule for implementation and an expected in-service date that considers lead timesnecessary to implement the plan. Failure to provide such summary may lead to noncompliance that couldresult in penalties and sanctions.

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Standard TPL-003-Ob - System Performance Following Loss of Two or More BES Elements

A. Introduction

1. Title: System Performance Following Loss of Two or More Bulk Electric SystemElements (Category C)

2. Number: TPL-003-Ob

3. Purpose: System simulations and associated assessments are needed periodically to ensurethat reliable systems are developed that meet specified performance requirements, withsufficient lead time and continue to be modified or upgraded as necessary to meet present andfuture System needs.

4. Applicability:



5. Effective Date: April 23, 2010

B. Requirements

R1. The Planning Authority and Transmission Planner shall each demonstrate through a validassessment that its portion of the interconnected transmission systems is planned such that thenetwork can be operated to supply projected customer demands and projected Firm (non-recallable reserved) Transmission Services, at all demand Levels over the range of forecastsystem demands, under the contingency conditions as defined in Category C of Table I(attached). The controlled interruption of customer Demand, the planned removal ofgenerators, or the Curtailment of firm (non-recallable reserved) power transfers may benecessary to meet this standard. To be valid, the Planning Authority and Transmission Plannerassessments shall:



R1.3. Be supported by a current or past study and/or system simulation testing thataddresses each of the following categories, showing system performance followingCategory C of Table 1(multiple contingencies). The specific elements selected (fromeach of the following categories) for inclusion in these studies and simulations shallbe acceptable to the associated Regional Reliability Organization(s).

R1.3.1. Be performed and evaluated only for those Category C contingencies thatwould produce the more severe system results or impacts. The rationale forthe contingencies selected for evaluation shall be available as supportinginformation. An explanation of why the remaining simulations wouldproduce less severe system results shall be available as supportinginformation.

R1.3.2. Cover critical system conditions and study years as deemed appropriate bythe responsible entity.


R1.3.4. Be conducted beyond the five-year horizon only as needed to addressidentified marginal conditions that may have longer lead-time solutions.


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R1.3.6. Be performed and evaluated for selected demand levels over the range offorecast system demands.

R1.3.7. Demonstrate that System performance meets Table 1 for Category Ccontingencies.


R1.3.9. Include Reactive Power resources to ensure that adequate reactive resourcesare available to meet System performance.

R1.3.10. Include the effects of existing and planned protection systems, including anybackup or redundant systems.


R1.3.12. Include the planned (including maintenance) outage of any bulk electricequipment (including protection systems or their components) at thoseDemand levels for which planned (including maintenance) outages areperformed.

R1.4. Address any planned upgrades needed to meet the performance requirements ofCategory C.

R1.5. Consider all contingencies applicable to Category C.

R2. When system simulations indicate an inability of the systems to respond as prescribed inReliability Standard TPL-003-0_R1, the Planning Authority and Transmission Planner shall each:

R2.1. Provide a written summary of its plans to achieve the required system performance asdescribed above throughout the planning horizon:


R2.1.2. Including a discussion of expected required in-service dates of facilities.


R2.2. Review, in subsequent annual assessments, (where sufficient lead time exists), thecontinuing need for identified system facilities. Detailed implementation plans are notneeded.

R3. The Planning Authority and Transmission Planner shall each document the results of theseReliability Assessments and corrective plans and shall annually provide these to its respectiveNERC Regional Reliability Organization(s), as required by the Regional ReliabilityOrganization.

C. Measures

Ml. The Planning Authority and Transmission Planner shall have a valid assessment and correctiveplans as specified in Reliability Standard TPL-003-0_R1 and TPL-003-0_R2.

M2. The Planning Authority and Transmission Planner shall have evidence it reporteddocumentation of results of its reliability assessments and corrective plans per ReliabilityStandard TPL-003-0 R3.

D. Compliance

Compliance Monitoring Process

1.1. Compliance Monitoring Responsibility

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Compliance Monitor: Regional Reliability Organizations.

1.2. Compliance Monitoring Period and Reset Timeframe

Annually.

1.3. Data Retention

None specified.


None.



2.2. Level 2: A valid assessment and corrective plan for the longer-term planning horizonis not available.


2.4. Level 4: A valid assessment and corrective plan for the near-term planning horizon isnot available.


1. None identified.

Version History

Version Date Action Change Tracking0 February 8, 2005 Adopted by NERC Board of Trustees New0 April 1, 2005 Effective Date New0 April 1, 2005 Add parenthesis to item "e" on page 8. Errata

Oa July 30, 2008 Adopted by NERC Board of Trustees

Oa October 23, 2008 Added Appendix 1- Interpretation of TPL-002-0 Requirements R1.3.2 and R1.3.12 andTPL-003-0 Requirements R1.3.2 and R1.3.12for Ameren and MISO

Revised

Oa April 23, 2010 FERC approval of interpretation of TPL-003-0 R1.3.12

Interpretation

Ob February 7, 2013 Interpretation adopted by NERC Board ofTrustees

Ob June 20, 2013 FERC order issued approving Interpretation

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Standard TPL-003-Ob - System Performance Followina Loss of Two or More RFS Fip.,,p.,+a

Table I. Transmission System Standards -Normal and Emergency Conditions

Category Contingencies System Limits or Impacts

System Stableand both

Thermal and Loss of Demand

Initiating Event(s) and Contin enc Voltage or Cascading °g yElement(s) Limits within Curtailed Firm Outages



Single Line Ground (SLG) or 3-Phase (30) Fault,B with Normal Clearing Yes No b NoEvent resulting in 1. Generator Yes No b Nothe loss of a single 2 Transmission Circuit Yes No b Noelement 3. Transformer Yes No b No

Loss of an Element without a Fault

Single Pole Block, Normal Cleartnge.4 Single Pole (dc) Line Yes Noh No

SLG Fault, with Normal Clearinge

Event(s) Cresulting in1. Bus Section Yes Planned/

'No

the loss of two ormore (multiple)

2 Breaker (failure or internal Fault) YesControlled

Planned/ NoControlled'elements.

SLG or 30 Fault, with Normal Clearinge, ManualSystem Adjustments, followed by another SLG or

30 Fault, with Normal Clearinge3 CategoryB(B1, B2, B3, or B4)

Yes Planned/ No

contingency, manual system adjustments,Controlled'

followed by another Category B (B 1, B2,B3, or B4) contin enc

Bipolar Block, with Normal Clearmge4 Bipolar (dc) Line Fault (non 30), with Planned/

Normal Clearinge Yes Controlled' No

5. Any two circuits of a multiple circuittowerlinef

Yes Planned/ NoControlled`

SLG Fault, with Delayed Clearinge (stuck breakeror protection system failure)

6 Generator Yes Planned/ NoControlled'

7. Transformer Yes Planned/ NoControlled'

8 Transmission Circuit Yes Planned/ NoControlled'

9 Bus Section Yes Planned/ NoControlled'

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Standard TPL-003-Ob - System Performance Following Loss of Two or More BESElements

D° 30 Fault, with Delayed Clearing e (stuck breaker or protection system Evaluate for risks and


two or more (multiple)elements removed or

1 Generator 3 Transformer • May involve substantial loss of

Cascading out of service 2 Transmission Circuit 4 Bus Sectioncustomer Demand andgeneration in a widespreadarea or areas

n Portions or all of the

30 Fault, with Normal Clearinge interconnected systems mayor may not achieve a new,

5 Breaker (failure or internal Fault) stable operating point° n Evaluation of these events may

6 Loss of towerline with three or more circuits require joint studies with

7 All transmission lines on a common right-of wayneighboring systems.

8. Loss of a substation (one voltage level plus transformers)9 Loss of a switching station (one voltage level plus transformers)

10 Loss of all generating units at a station


12. Failure of a fully redundant Special Protection System (orremedial action scheme) to operate when required


14 Impact of severe power swings or oscillations from Disturbancesin another Regional Reliability Organization

a) Applicable rating refers to the applicable Normal and Emergency facility thermal Rating or system voltage limit asdetermined and consistently applied by the system or facility owner. Applicable Ratings may include Emergency Ratingsapplicable for short durations as required to permit operating steps necessary to maintain system control. All Ratingsmust be established consistent with applicable NERC Reliability Standards addressing Facility Ratings.

b) Planned or controlled interruption of electric supply to radial customers or some local Network customers, connected to orsupplied by the Faulted element or by the affected area, may occur in certain areas without impacting the overallreliability of the interconnected transmission systems. To prepare for the next contingency, system adjustments arepermitted, including curtailments of contracted Firm (non-recallable reserved) electric power Transfers.

c) Depending on system design and expected system impacts, the controlled interruption of electric supply to customers(load shedding), the planned removal from service of certain generators, and/or the curtailment of contracted Firm (non-recallable reserved) electric power transfers may be necessary to maintain the overall reliability of the interconnectedtransmission systems.




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Appendix I

Interpretation of TPL-002-0 Requirements R1.3.2 and R1.3.12 and TPL-003-0Requirements R1.3.2 and R1.3.12 for Ameren and MISO

NERC received two requests for interpretation of identical requirements (Requirements R1.3.2 andR1.3.12) in TPL-002-0 and TPL-003-0 from the Midwest ISO and Ameren. These requirements state:

TPL-002-0:


of the following categories, showing system performance following Category B of Table 1(single contingencies). The specific elements selected (from each of the following categories)for inclusion in these studies and simulations shall be acceptable to the associated RegionalReliability Organization(s).


R1.3.12 Include the planned ( including maintenance) outage of any bulk electric equipment(including protection systems or their components) at those demand levels for whichplanned (including maintenance) outages are performed.

TPL-003-0:


of the following categories, showing system performance following Category C of Table 1(multiple contingencies). The specific elements selected (from each of the followingcategories) for inclusion in these studies and simulations shall be acceptable to the associatedRegional Reliability Organization(s).



Requirement R1.3.2

Request for Interpretation of TPL-002-0 and TPL-003-0 Requirement R1.3.2Received from Ameren on July 25, 2007:Ameren specifically requests clarification on the phrase, `critical system conditions' in R1.3.2. Amerenasks if compliance with R1.3.2 requires multiple contingent generating unit Outages as part of possiblegeneration dispatch scenarios describing critical system conditions for which the system shall be plannedand modeled in accordance with the contingency definitions included in Table 1.

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Request for Interpretation of TPL-002-0 and TPL-003-0 Requirement R1.3.2Received from MISO on August 9, 2007:MISO asks if the TPL standards require that any specific dispatch be applied, other than one that isrepresentative of supply offirm demand and transmission service commitments, in the modeling of systemcontingencies specified in Table 1 in the TPL standards.

MISO then asks if a variety of possible dispatch patterns should be included in planning analysesincluding a probabilistically based dispatch that is representative of generation deficiency scenarios,would it be an appropriate application of the TPL standard to apply the transmission contingencyconditions in Category B of Table 1 to these possible dispatch pattern.


The selection of a credible generation dispatch for the modeling of critical system conditions is within thediscretion of the Planning Authority. The Planning Authority was renamed "Planning Coordinator" (PC)in the Functional Model dated February 13, 2007. (TPL -002 and -003 use the former "PlanningAuthority" name, and the Functional Model terminology was a change in name only and did not affectresponsibilities.)

- Under the Functional Model, the Planning Coordinator "Provides and informs Resource Planners,Transmission Planners, and adjacent Planning Coordinators of the methodologies and tools for thesimulation of the transmission system" while the Transmission Planner "Receives from the PlanningCoordinator methodologies and tools for the analysis and development of transmission expansionplans." A PC's selection of "critical system conditions" and its associated generation dispatch fallswithin the purview of "methodology."

Furthermore, consistent with this interpretation, a Planning Coordinator would formulate critical systemconditions that may involve a range of critical generator unit outages as part of the possible generatordispatch scenarios.

Both TPL-002-0 and TPL-003-0 have a similar measure M1:

M1. The Planning Authority and Transmission Planner shall have a valid assessment andcorrective plans as specified in Reliability Standard TPL-002-0_R1 [or TPL-003-0 R1]and TPL-002-0_R2 [or TPL-003-0_R2]." -

The Regional Reliability Organization (RRO) is named as the Compliance Monitor in both standards.Pursuant to Federal Energy Regulatory Commission (FERC) Order 693, FERC eliminated the RRO as theappropriate Compliance Monitor for standards and replaced it with the Regional Entity (RE). Seeparagraph 157 of Order 693. Although the referenced TPL standards still include the reference to theRRO, to be consistent with Order 693, the RRO is replaced by the RE as the Compliance Monitor for thisinterpretation. As the Compliance Monitor, the RE determines what a "valid assessment" means whenevaluating studies based upon specific sub-requirements in R1.3 selected by the Planning Coordinator andthe Transmission Planner. If a PC has Transmission Planners in more than one region, the REs mustcoordinate among themselves on compliance matters.

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Requirement R1.3.12

Request for Interpretation of TPL-002-0 and TPL-003-0 Requirement R1.3.12Received from Ameren on July 25, 2007:Ameren also asks how the inclusion ofplanned outages should be interpreted with respect to thecontingency definitions specified in Table 1 for Categories B and C. Specifically, Ameren asks if R1.3.12requires that the system be planned to be operated during those conditions associated with plannedoutages consistent with the performance requirements described in Table 1 plus any unidentified outage.

Request for Interpretation of TPL-002-0 and TPL-003-0 Requirement R1.3.12Received from MISO on August 9, 2007:MISO asks if the term "planned outages " means only already known/scheduled planned outages that maycontinue into the planning horizon, or does it include potential planned outages not yet scheduled thatmay occur at those demand levels for which planned (including maintenance) outages are performed?

If the requirement does include not yet scheduled but potential planned outages that could occur in theplanning horizon, is the following a proper interpretation of this provision?

The system is adequately planned and in accordance with the standard if, in order for a system operatorto potentially schedule such a planned outage on the future planned system, planning studies show that asystem adjustment (load shed, re-dispatch ofgenerating units in the interconnection, or system

reconfiguration) would be required concurrent with taking such a planned outage in order to prepare fora Category B contingency (single element forced out of service)? In other words, should the system ineffect be planned to be operated as for a Category C3 n-2 event, even though the first event is a plannedbase condition?

If the requirement is intended to mean only known and scheduled planned outages that will occur or maycontinue into the planning horizon, is this interpretation consistent with the original interpretation byNERC of the standard as provided by NERC in response to industry questions in the Phase I developmentof this standard]?


This provision was not previously interpreted by NERC since its approval by FERC and other regulatoryauthorities. TPL-002-0 and TPL-003-0 explicitly provide that the inclusion of planned (includingmaintenance) outages of any bulk electric equipment at demand levels for which the planned outages arerequired. For studies that include planned outages, compliance with the contingency assessment for TPL-002-0 and TPL-003-0 as outlined in Table I would include any necessary system adjustments whichmight be required to accommodate planned outages since a planned outage is not a "contingency" asdefined in the NERC Glossary of Terms Used in Standards.

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Appendix 2

- • - . • ! ! "- s• - • '-• - • ° • - . • • • 1! !.^ . .-• ! ® • • • !!, ! •-• . ^ ® ® ,• ' • - • • • • • •

Date submitted: December 12, 2011

The following interpretations of TPL-003-0a, System Performance Following Loss of Two or More BulkElectric System Elements (Category C), Requirements R1.3.1, R1.3.10 and R1.5 and TPL-004-0, SystemPerformance Following Extreme Events Resulting in the Loss of Two or More Bulk Electric SystemElements (Category D), Requirements R1.3.1, R1.37 and R1.4 were developed by members of the AssessTransmission Future Needs Standard Drafting Team (ATFNSTD), Protection System MisoperationsStandard Development Team (PSMSDT), and Protection System Maintenance and Testing StandardDrafting Team (PSMTSDT).

•. • Requiremeht •

TPL-003-Oa R1.3.1 Be performed and evaluated only for those Category C contingencies thatwould produce the more severe system results or impacts. The rationale for thecontingencies selected for evaluation shall be available as supporting information.An explanation of why the remaining simulations would produce less severe systemresults shall be available as supporting information.

TPL-003-Oa 111.3.10. Include the effects of existing and planned protection systems, includingany backup or redundant systems.

TPL-003-Oa R1.5. Consider all contingencies applicable to Category C.

TPL-004-0 R1.3.1. Be performed and evaluated only for those Category D contingencies thatwould produce the more severe system results or impacts. The rationale for thecontingencies selected for evaluation shall be available as supporting information.An explanation of why the remaining simulations would produce less severe systemresults shall be available as supporting information.

TPL-004-0 R1.3.7. Include the effects of existing and planned protection systems, including anybackup or redundant systems.

TPL-004-0 R1.4. Consider all contingencies applicable to Category D.

r • • -i-• • -,r

This interpretation request has been developed to address Commission concerns related to the term"Single Point of Failure" and how it relates to system performance and contingency planning

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clarification regarding the following questions about the listed standards, requirements and terms.More specifically, clarification is needed about the comprehensive study of system performance

relating to Table 1's, Category C and D contingency of a "protection system failure" and specifically theimpact of failed components (i.e., "Single Point of Failure"). It is not entirely clear whether a validassessment of a protection system failure includes evaluation of shared or non-redundant protectionsystem components. Protection systems that have a shared protection system component are not twoindependent protection systems, because both protection systems will be mutually impacted for afailure of a single shared component. A protection system component evaluation would include theevaluation of the consequences on system performance for the failure of any protection systemcomponent that is integral to the operation of the protection system being evaluated and to theoperation of another protection system.

On March 30, 2009, NERC issued an Industry Advisory - Protection System Single Point of Failurel (i.e.,NERC Alert) for three significant events. One of which, the Westwing outage (June 14, 2004) wascaused by failure of a single auxiliary relay that initiated both breaker tripping and the breaker failureprotection. Since breaker tripping and breaker failure protection both shared the same auxiliary relay,there was no independence between breaker tripping and breaker failure protection systems, thereforecausing both protection systems to not operate for the single component failure of the auxiliary relay.The failure of this auxiliary relay is known as a "single point of failure." It is not clear whether thissituation is comprehensively addressed by the applicable entities when making a valid assessment ofsystem performance for both Category C and D contingencies.

Question 1: For the parenthetical "(stuck breaker or protection system failure)" in TPL-003-Oa (CategoryC contingencies 6-9) and TPL-004-0 (Category D contingencies 1-4), does an entity have the option ofevaluating the effects2 of either "stuck breaker" or "protection system failure" contingency3, or does anapplicable entity have to evaluate the contingency that produces the more severe system results orimpacts as identified in R1.3.1 of both standards?

There is a lack of clarity whether R1.3.14 requires an entity to assess which contingency causes the mostsevere system results or impacts (R1.3.1) and this ambiguity could result in a potential reliability gap.Whether the simulation of a stuck breaker or protection system failure will produce the worst resultdepends on the protection system design. For example when a protection system is fully redundant, aprotection system failure will not affect fault clearing; therefore, a stuck breaker would result in moresevere system results or impacts. However, when a protection system failure affects fault clearing, thefault clearing time may be longer than the breaker failure protection clearing time for a stuck breakercontingency and may result in tripping of additional system elements, resulting in a more severe system

1 NERC Website: (http://www.nerc.com/fileUploads/File/Events%20Analvsis/A 2009 03 30 01 pdf)2As required by NERC Reliability Standard TPL-003-0a, Requirement R1.3.10. and/or TPL-004-0, Requirement

R1.3.7.

3 As required by NERC Reliability Standard TPL-003-0a, Requirement R1.5. and/or TPL-004-0, Requirement R1.4."Be'performed and evaluated only for those Category (TPL-003-Oa Category C and TPL-004-0 Category D)

contingencies that would produce the more severe system results or impacts."

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response.

Question 2: For the phrase "Delayed Clearing5i used in Category C6 contingencies 6-9 and Category D'contingencies 1-4, to what extent does the description in Table 1, footnote (e)8 require an entity tomodel a single point of failure of a protection system component that may prevent correct operation ofa protection system, including other protection systems impacted by that failed component based onthe as-built design of that protection system?

There is a lack of clarity whether footnote (e) in Table 1 requires the study and/or simulation of a failureof a protection system component (i.e., single point of failure) that may prevent correct operation ofthe protection system(s) impacted by the component failure. Protection systems that share aprotection system component are fully dependent upon the correct operation of that single sharedcomponent and do not perform as two independent protection systems. This lack of clarity may resultin a potential reliability gap.

Clarity is necessary as to whether (1) a valid assessment should include evaluation of delayed clearingdue to failure of the protection system component (i.e., single point of failure), such as the failure of ashared protection system component, that produces the more severe system results or impacts; and (2)the study and/or simulation of the fault clearing sequence and protection system(s) operation shouldbe based on the protection system(s) as-built design.

The lack of clarity is compounded by the similarity between the phrase "Delayed Clearing" used in TPL-003-Oa and TPL-004-0, footnote (e), and the NERC glossary term "Delayed Fault Clearing." While TPL-003-Oa and TPL-004-0 do not use the glossary term, the similarity may lead to confusion andinconsistency in how entities apply footnote (e) to "stuck breaker" or "protection system failure"contingency assessments.

For the parenthetical "(stuck breaker or protection system failure)" in TPL-003-Oa (Category Ccontingencies 6-9) and TPL-004-0 (Category D contingencies 1-4), does an entity have the option ofevaluating the effects9 of either "stuck breaker" or "protection system failure" contingency10, or doesan applicable entity have to evaluate the contingency that produces the more severe system results orimpacts as identified in R1.3.1 of both standards?

5 As required by NERC Reliability Standard TPL-003-0a, Requirement R1.5. and/or TPL-004-0, Requirement R1.4.6 As required by NERC Reliability Standard TPL-003-0a, Requirement R1.5.' As required by NERC Reliability Standard TPL-004-0, Requirement R1.4.

8 Footnote (e) Delayed Clearing: "failure of any protection system component such as a relay, circuit breaker, orcurrent transformer, and not because of an intentional design delay,"9 As required by NERC Reliability Standard TPL-003-Oa, Requirement R1.3.10. and/or TPL-004-0, RequirementR1.3.7.

10 As required by NERC Reliability Standard TPL-003-0a, Requirement R1.5. and/or TPL-004-0, Requirement R1.4.

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The interpretation drafting team concludes that the Planning Authority and Transmission Planner must

evaluate the situation that produces the more severe system results or impacts (i.e., TPL-003-0a, R1.3.1

and TPL-004-0, R1.3.1) due to a delayed clearing condition regardless of whether the condition resulted

from a stuck breaker or protection system failure. The Reliability Standards TPL-003-Oa (Table I,

Category C contingencies 6-9) and TPL-004-0 (Table I, Category D contingencies 1-4) involve an

assessment of the effects of either a stuck breaker or a protection system failure. The single line

ground (SLG) (TPL-003-0a, Table I, Category C) Fault and 3-phase (30) (TPL-004-0, Table I, Category D)

Fault contingencies with delayed clearing are further defined by footnote (e) and the parenthetical

phrase "(stuck breaker or protection system failure)." Footnote (e) explains that "Delayed clearing of a

Fault is due to failure of any protection system component such as a relay, circuit breaker, or current

transformer, and not because of an intentional design delay." The parenthetical further emphasizes

that the failure may be a "stuck breaker or protection system failure" that causes the delayed clearing

of the fault. The text in Table 1 in either standard explains that when selecting delayed clearing

contingencies to evaluate, both conditions "(stuck breaker or protection system failure)" must beconsidered.

For the phrase "Delayed Clearing11i used in Category C12 contingencies 6-9 and Category D13

contingencies 1-4, to what extent does the description in Table 1, footnote (e) 14 require an entity tomodel a single point of failure of a protection system component that may prevent correct operation ofa protection system, including other protection systems impacted by that failed component based onthe as-built design of that protection system?

The term "Delayed Clearing" that is described in Table I, footnote (e) refers to fault clearing that resultsfrom a failure to achieve the protection system's normally expected clearing time. For Category C or Dcontingencies, each Planning Authority and Transmission Planner is permitted engineering judgment inits selection of the protection system component failures for evaluation that would produce the moresevere system results or impact (i.e., TPL-003-0a, R1.3.1 and TPL-004-0, R1.3.1). The evaluation wouldinclude addressing all protection systems affected by the selected component.

A protection system component failure that impacts one or more protection systems and increases thetotal fault clearing time requires the Planning Authority and Transmission Planner to simulate the full

11As required by NERC Reliability Standard TPL-003-0a, Requirement R1.5. and/or TPL-004-0, Requirement R1.4.

12 As required by NERC Reliability Standard TPL-003-Oa, Requirement R1.5.13 As required by NERC Reliability Standard TPL-004-0, Requirement R1.4.

14 Footnote (e) Delayed Clearing: "failure of any protection system component such as a relay, circuit breaker, orcurrent transformer, and not because of an intentional design delay,"

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impact (clearing time and facilities removed) on the Bulk Electric System performance.

The interpretation drafting team bases this conclusion on the footnote (e) example "...any protectionsystem component such as, relay, circuit breaker, or current transformer..." because the component"circuit breaker" is not addressed in the current or previously defined NERC glossary term. Theinterpretation drafting team initially believed the lowercase usage of "protection system" inferred theNERC glossary term and the components described therein; however, based on the interpretationdrafting team's further assessment of footnote (e), it concludes that the existing TPL standards (TPL-003-Oa and TPL-004-0) do not implicitly use the NERC glossary term. Without an explicit reference tothe NERC glossary term, "Protection System," the two standards do not prescribe the specificprotection system components that must be addressed by the Planning Authority and TransmissionPlanner in performing the studies required in TPL-003-Oa and TPL-004-0.

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Standard TPL-004-Oa- System Performance Following Extreme BES Events

A. Introduction

1. Title: System Performance Following Extreme Events Resulting in the Loss of Two orMore Bulk Electric System Elements (Category D)

2. Number: TPL-004-Oa

3. Purpose: System simulations and associated assessments are needed periodically to ensure thatreliable systems are developed that meet specified performance requirements, with sufficientlead time and continue to be modified or upgraded as necessary to meet present and futureSystem needs.

4. Applicability:



5. Effective Date: April 1, 2005

B. Requirements

RI. The Planning Authority and Transmission Planner shall each demonstrate through a validassessment that its portion of the interconnected transmission system is evaluated for the risksand consequences of a number of each of the extreme contingencies that are listed underCategory D of Table I. To be valid, the Planning Authority's and Transmission Planner'sassessment shall:

111.1. Be made annually.

R1.2. Be conducted for near-term (years one through five).

R1.3. Be supported by a current or past study and/or system simulation testing thataddresses each of the following categories, showing system performance followingCategory D contingencies of Table I. The specific elements selected (from withineach of the following categories) for inclusion in these studies and simulations shallbe acceptable to the associated Regional Reliability Organization(s).

R1.3.1. Be performed and evaluated only for those Category D contingencies that wouldproduce the more severe system results or impacts. The rationale for thecontingencies selected for evaluation shall be available as supportinginformation. An explanation of why the remaining simulations would produceless severe system results shall be available as supporting information.

111.3.2. Cover critical system conditions and study years as deemed appropriate by theresponsible entity.




111.3.6. Include Reactive Power resources to ensure that adequate reactive resourcesare available to meet system performance.

111.3.7. Include the effects of existing and planned protection systems, including anybackup or redundant systems.


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R1.3.9. Include the planned (including maintenance) outage of any bulk electricequipment (including protection systems or their components) at those demandlevels for which planned (including maintenance) outages are performed.

R1.4. Consider all contingencies applicable to Category D.

R2. The Planning Authority and Transmission Planner shall each document the results of itsreliability assessments and shall annually provide the results to its entities' respective NERCRegional Reliability Organization(s), as required by the Regional Reliability Organization.

C. Measures

Ml. The Planning Authority and Transmission Planner shall have a valid assessment for its systemresponses as specified in Reliability Standard TPL-004-0_R1.

M2. The Planning Authority and Transmission Planner shall provide evidence to its ComplianceMonitor that it reported documentation of results of its reliability assessments per ReliabilityStandard TPL-004-0 Rl.

D. Compliance

1. Compliance Monitoring Process

I.I. Compliance Monitoring Responsibility

Compliance Monitor: Regional Reliability Organization.

Each Compliance Monitor shall report compliance and violations to NERC via theNERC Compliance Reporting Process.

1.2. Compliance Monitoring Period and Reset TimeframeAnnually.

1.3. Data Retention

None specified.


None.


2.1. Level 1: A valid assessment, as defined above, for the near-term planning horizonis not available.



2.4. Level 4: Not applicable.E. Regional Differences

1. None identified.

Version History

Version Date Action Change Tracking0 April 1, 2005 Effective Date New

Oa February 7, 2013 Interpretation adopted by NERC Board ofTrustees

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I Oa I June 20, 20] 3 1 Interpretation approved in FERC order I I

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Category Contingencies System Limits or ImpactsSystem Stable

and bothThermal and Loss of Demand

Initiating Event(s) and Contingency Voltage or CascadingElement(s) Limits within Curtailed Firm Outages


ANo Contingencies

All Facilities in Service Yes No No

Single Line Ground (SLG) or 3-Phase (30) Fault,B

Event resulting inwith Normal Clearing

I GeneratorYes No b No

the loss of a single 2 Transmission CircuitYesYes

bNo b

Noelement. 3 Transformer Yes No b

NoNoLoss of an Element without a Fault

Single Pole Block, Normal Clearinge4 Single Pole (dc) Line Yes Nob No

eC SLG Fault, with Normal Clearing

Event(s) resulting inI Bus Section Yes Planned/ No

the loss oftwo ormore (multiple)

2 Breaker (failure or internal Fault) YesControlled`Planned/ No

element Controlled°sSLG or 30 Fault, with Normal Clearinge, ManualSystem Adjustments, followed by another SLG or

30 Fault, with Normal Clearinge3 Category B (B 1, B2, B3, or B4) Yes Planned/ No

contingency, manual system adjustments Controlled',followed by another Category B (B 1, B2,B3, or B4) contingency


Normal Clearinge- Yes Controlled' No

5 Any two circuits of a multiple circuitYetowerlmer s Planned/ No

Controlled°SLG Fault, with Delayed Clearmge (stuck breakeror protection system failure)

6. Generator Yes Planned/ NoControlled`

7 Transformer Yes Planned/ NoControlled'

8 Transmission Circuit Yes Planned/ NoControlled'

9. Bus Section Yes Planned/ NoControlled`

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D° 30 Fault, with Delayed Clearinge (stuck breaker or protection system Evaluate for risks and


two or more (multiple) I Generator 3 Transformer ' May involve substantial loss ofelements removed or customer Demand andCascading out of service 2 Transmission Circuit 4 Bus Section generation in a widespread

area or areas• Portions or all of the

30 Fault, with Normal Clearing interconnected systems mayor may not achieve a new,

5. Breaker (failure or internal Fault) stable operating point^ n Evaluation of these events may

6 Loss of towerline with three or more circuits requirejoint studies with

7 All transmission lines on a common right-of wayneighboring systems

8 Loss of a substation (one voltage level plus transformers)

9 Loss of a switching station (one voltage level plus transformers)

10. Loss of all generating units at a station

1 I Loss of a large Load or major Load center

12 Failure of a fully redundant Special Protection System (orremedial action scheme) to operate when required


14. Impact of severe power swings or oscillations from Disturbancesin another Regional Reliability Organization

a) Applicable rating refers to the applicable Normal and Emergency facility thermal Rating or System Voltage Limit asdetermined and consistently applied by the system or facility owner. Applicable Ratings may include Emergency Ratingsapplicable for short durations as required to permit operating steps necessary to maintain system control. All Ratingsmust be established consistent with applicable NERC Reliability Standards addressing Facility Ratings.

b) Planned or controlled interruption of electric supply to radial customers or some local network customers, connected to orsupplied by the Faulted element or by the affected area, may occur in certain areas without impacting the overallreliability of the interconnected transmission systems. To prepare for the next contingency, system adjustments arepermitted, including curtailments of contracted Firm (non-recallable reserved) electric power Transfers.

c) Depending on system design and expected system impacts, the controlled interruption of electric supply to customers(load shedding), the planned removal from service of certain generators, and/or the curtailment of contracted Firm (non-recallable reserved) electric power Transfers may be necessary to maintain the overall reliability of the interconnectedtransmission systems.




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Appendix 1

Date submitted: I December 12, 2011

The following interpretations of TPL-003-0a, System Performance Following Loss of Two or More BulkElectric System Elements (Category C), Requirements R1.3.1, R1.3.10 and R1.5 and TPL-004-0, SystemPerformance Following Extreme Events Resulting in the Loss of Two or More Bulk Electric SystemElements (Category D), Requirements R1.3.1, R1.37 and R1.4 were developed by members of the AssessTransmission Future Needs Standard Drafting Team (ATFNSTD), Protection System MisoperationsStandard Development Team (PSMSDT), and Protection System Maintenance and Testing StandardDrafting Team (PSMTSDT).

TPL-003-Oa R1.3.1 Be performed and evaluated only for those Category C contingencies thatwould produce the more severe system results or impacts. The rationale for thecontingencies selected for evaluation shall be available as supporting information.An explanation of why the remaining simulations would produce less severe systemresults shall be available as supporting information.

TPL-003-Oa 111.3.10. Include the effects of existing and planned protection systems, includingany backup or redundant systems.

TPL-003-Oa R1.5. Consider all contingencies applicable to Category C.

TPL-004-0 R1.3.1. Be performed and evaluated only for those Category D contingencies thatwould produce the more severe system results or impacts. The rationale for thecontingencies selected for evaluation shall be available as supporting information.An explanation of why the remaining simulations would produce less severe systemresults shall be available as supporting information.

TPL-004-0 R1.3.7. Include the effects of existing and planned protection systems, including anybackup or redundant systems.

TPL-004-0 R1.4. Consider all contingencies applicable to Category D.

This interpretation request has been developed to address Commission concerns related to the term"Single Point of Failure" and how it relates to system performance and contingency planningclarification regarding the following questions about the listed standards, requirements and terms.

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More specifically, clarification is needed about the comprehensive study of system performancerelating to Table 1's, Category C and D contingency of a "protection system failure" and specifically theimpact of failed components (i.e., "Single Point of Failure"). It is not entirely clear whether a validassessment of a protection system failure includes evaluation of shared or non-redundant protectionsystem components. Protection systems that have a shared protection system component are not twoindependent protection systems, because both protection systems will be mutually impacted for afailure of a single shared component. A protection system component evaluation would include theevaluation of the consequences on system performance for the failure of any protection systemcomponent that is integral to the operation of the protection system being evaluated and to theoperation of another protection system.

On March 30, 2009, NERC issued an Industry Advisory - Protection System Single Point of Failure1(i.e.,NERC Alert) for three significant events. One of which, the Westwing outage (June 14, 2004) wascaused by failure of a single auxiliary relay that initiated both breaker tripping and the breaker failureprotection. Since breaker tripping and breaker failure protection both shared the same auxiliary relay,there was no independence between breaker tripping and breaker failure protection systems, thereforecausing both protection systems to not operate for the single component failure of the auxiliary relay.The failure of this auxiliary relay is known as a "single point of failure." It is not clear whether thissituation is comprehensively addressed by the applicable entities when making a valid assessment ofsystem performance for both Category C and D contingencies.

Question 1: For the parenthetical "(stuck breaker or protection system failure)" in TPL-003-Oa (CategoryC contingencies 6-9) and TPL-004-0 (Category D contingencies 1-4), does an entity have the option ofevaluating the effectsz of either "stuck breaker" or "protection system failure" contingency3, or does anapplicable entity have to evaluate the contingency that produces the more severe system results orimpacts as identified in R1.3.1 of both standards?

There is a lack of clarity whether R1.3.14 requires an entity to assess which contingency causes the mostsevere system results or impacts (R1.3.1) and this ambiguity could result in a potential reliability gap.Whether the simulation of a stuck breaker or protection system failure will produce the worst resultdepends on the protection system design. For example when a protection system is fully redundant, aprotection system failure will not affect fault clearing; therefore, a stuck breaker would result in moresevere system results or impacts. However, when a protection system failure affects fault clearing, thefault clearing time may be longer than the breaker failure protection clearing time for a stuck breakercontingency and may result in tripping of additional system elements, resulting in a more severe systemresponse.

Question 2: For the phrase "Delayed Clearings" used in Category C6 contingencies 6-9 and Category D'contingencies 1-4, to what extent does the description in Table 1, footnote (e)8 require an entity to

1 NERC Website: (http://www.nerc.com/fileUgloads/File/Events%20Analysis/A-2009-03-30-01 pdf)

2 As required by NERC Reliability Standard TPL-003-0a, Requirement R1.3.10. and/orTPL-004-0, RequirementR1.3.7.

3 As required by NERC Reliability Standard TPL-003-0a, Requirement R1.5. and/or TPL-004-0, Requirement R1.4.4"Be performed and evaluated only for those Category (TPL-003-Oa Category C and TPL-004-0 Category D)contingencies that would produce the more severe system results or impacts."


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model a single point of failure of a protection system component that may prevent correct operation ofa protection system, including other protection systems impacted by that failed component based onthe as-built design of that protection system?

There is a lack of clarity whether footnote (e) in Table 1 requires the study and/or simulation of a failureof a protection system component (i.e., single point of failure) that may prevent correct operation ofthe protection system(s) impacted by the component failure. Protection systems that share aprotection system component are fully dependent upon the correct operation of that single shared

component and do not perform as two independent protection systems. This lack of clarity may resultin a potential reliability gap.

Clarity is necessary as to whether (1) a valid assessment should include evaluation of delayed clearingdue to failure of the protection system component (i.e., single point of failure), such as the failure of ashared protection system component, that produces the more severe system results or impacts; and (2)the study and/or simulation of the fault clearing sequence and protection system(s) operation shouldbe based on the protection system(s) as-built design.

The lack of clarity is compounded by the similarity between the phrase "Delayed Clearing" used in TPL-003-Oa and TPL-004-0, footnote (e), and the NERC glossary term "Delayed Fault Clearing." While TPL-003-Oa and TPL-004-0 do not use the glossary term, the similarity may lead to confusion andinconsistency in how entities apply footnote (e) to "stuck breaker" or "protection system failure"contingency assessments.

For the parenthetical "(stuck breaker or protection system failure)" in TPL-003-Oa (Category Ccontingencies 6-9) and TPL-004-0 (Category D contingencies 1-4), does an entity have the option ofevaluating the effects9 of either "stuck breaker" or "protection system failure" contingency10, or doesan applicable entity have to evaluate the contingency that produces the more severe system results orimpacts as identified in R1.3.1 of both standards?

The interpretation drafting team concludes that the Planning Authority and Transmission Planner must

evaluate the situation that produces the more severe system results or impacts (i.e., TPL-003-0a, R1.3.1

and TPL-004-0. R1.3.1) due to a delayed clearing condition regardless of whether the condition resulted

6 As required by NERC Reliability Standard TPL-003-Oa, Requirement R1.5.

' As required by NERC Reliability Standard TPL-004-0, Requirement R1.4.

8 Footnote (e) Delayed Clearing: "failure of any protection system component such as a relay, circuit breaker, orcurrent transformer, and not because of an intentional design delay,"9 As required by NERC Reliability Standard TPL-003-0a, Requirement R1.3.10. and/or TPL-004-0, RequirementR1.3.7.


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from a stuck breaker or protection system failure. The Reliability Standards TPL-003-Oa (Table I,

Category C contingencies 6-9) and TPL-004-0 (Table I, Category D contingencies 1-4) involve an

assessment of the effects of either a stuck breaker or a protection system failure. The single line

ground (SLG) (TPL-003-0a, Table I, Category C) Fault and 3-phase (3o) (TPL-004-0, Table I, Category D)

Fault contingencies with delayed clearing are further defined by footnote (e) and the parenthetical

phrase "(stuck breaker or protection system failure)." Footnote (e) explains that "Delayed clearing of a

Fault is due to failure of any protection system component such as a relay, circuit breaker, or current

transformer, and not because of an intentional design delay." The parenthetical further emphasizes

that the failure may be a "stuck breaker or protection system failure" that causes the delayed clearing

of the fault. The text in Table 1 in either standard explains that when selecting delayed clearing

contingencies to evaluate, both conditions "(stuck breaker or protection system failure)" must beconsidered.

• .U es

For the phrase "Delayed Clearing11i used in Category Clz contingencies 6-9 and Category D13contingencies 1-4, to what extent does the description in Table 1, footnote (e)14 require an entity tomodel a single point of failure of a protection system component that may prevent correct operation ofa protection system, including other protection systems impacted by that failed component based onthe as-built design of that protection system?

`;..^•

The term "Delayed Clearing" that is described in Table I, footnote (e) refers to fault clearing that resultsfrom a failure to achieve the protection system's normally expected clearing time. For Category C or Dcontingencies, each Planning Authority and Transmission Planner is permitted engineering judgment inits selection of the protection system component failures for evaluation that would produce the moresevere system results or impact (i.e., TPL-003-0a, R1.3.1 and TPL-004-0, R1.3.1). The evaluation wouldinclude addressing all protection systems affected by the selected component.

A protection system component failure that impacts one or more protection systems and increases thetotal fault clearing time requires the Planning Authority and Transmission Planner to simulate the fullimpact (clearing time and facilities removed) on the Bulk Electric System performance.

The interpretation drafting team bases this conclusion on the footnote (e) example "...any protectionsystem component such as, relay, circuit breaker, or current transformer..." because the component"circuit breaker" is not addressed in the current or previously defined NERC glossary term. The

Linterpretation drafting team initially believed the lowercase usage of "protection system" inferred the

11 As required by NERC Reliability Standard TPL-003-0a, Requirement R1.5. and/or TPL-004-0, Requirement R1.4.12 As required by NERC Reliability Standard TPL-003-0a, Requirement R1.5.

13 As required by NERC Reliability Standard TPL-004-0, Requirement R1.4.

14 Footnote (e) Delayed Clearing: "failure of any protection system component such as a relay, circuit breaker, orcurrent transformer, and not because of an intentional design delay,"

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NERC glossary term and the components described therein; however, based on the interpretationdrafting team's further assessment of footnote (e), it concludes that the existing TPL standards (TPL-003-Oa and TPL-004-0) do not implicitly use the NERC glossary term. Without an explicit reference tothe NERC glossary term, "Protection System," the two standards do not prescribe the specificprotection system components that must be addressed by the Planning Authority and TransmissionPlanner in performing the studies required in TPL-003-Oa and TPL-004-0.

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