Transmission System Planning Performance
WECC Regional Criterion
TPL-001-WECC-CRT-3
Document Scope
This document is designed to address the substance of TPL-001-WECC-CRT-2.1, WECC Requirement WR3 and the requirements imposed by NERC TPL-001-4, Requirements R5 and R6.
Draft One
Draft One is designed to open an industry dialogue to ensure the direction of the draft aligns with the needs of the industry. Draft One is not intended to be a final work product; rather, is it the springboard from which the drafting team will proceed. The drafting team welcomes comments on all aspects of the document.
To assist the industry in this development process, Mr. Charles Matthews, the team’s chair, anticipates presentation of this document to the Planning Coordination Committee (PCC) during the October 7, 2014 meeting.
Measures and a Guidance Section will be developed once the substance of the Requirements is further developed.
Table W-1
Revision of Table W-1 is within the scope of this project. The drafting team understands that the Table is currently under review by the WECC Reliability Subcommittee (RS). The team will coordinate any changes with the RS.
Procedural Background
On September 5, 2012,the WECC Board of Directors (Board) adopted a recommendation by the Regional CriteriaWorkGroup(RCWG) changing the designation of this document from a WECC Criterion (CRT) to a WECC Regional Business Practice (RBP). On June 24, 2014, the Board reversed that decision and designated this document as a CRT.
In further keeping with the September 5, 2012 recommendation, on November 28, 2012, a Standards Authorization Request (SAR) was submitted to evaluate whether this document should be drafted as a WECC Regional Reliability Standard (RRS).
On December 19, 2012, the WSC accepted the WECC-0100 SAR as drafted with specific approval to assign an evaluation team to review the subject matter and return a recommendation to the WSC.
On June 26, 2013, the WSC approved the evaluation team’s recommendation to ballot the retirement of TPL-001-WECC-RBP-2.1, WR1, WR2, WR4 and WR5, coincident with the Effective Date of NERC’s TPL-001-4, because the content of the WECC Requirements will be resident in the NERC TPL.
On August 8, 2013, the WSC assigned the original drafting team, augmenting the team during later weeks.
On October 8, 2013, a WECC Ballot Pool voted to retire TPL-(012 through 014)-WECC-RBP-2.1, WR1, WR2, WR4 and WR5 of the Effective Date of NERC TPL-001-4. (The Effective Date is projected for approximately January 1, 2016. It should be noted that the TPL has a staggered Effective Date.)
On November 1, 2013, the WECC-0100 Drafting Team (DT):
1) Reported completion of the tasks assigned in the WECC-0100 Standard Authorization Request (SAR),
2) Requested the WECC Standards Committee (WSC) deem the WECC-0100 SAR complete; and,
3) Requested the WSC accept the DT’s recommendation to proceed with informal drafting in support of an iterative SAR tailored to the remedial needs of TPL-001-WECC-RBP-2.1, System Performance, WR3 as well as a more granular implementation plan of TPL-001-4, Transmission System Planning Performance Requirements Requirement R5 and R6.
In light of the retirement of the TPL-001-WECC-RBP-2’s Requirements WR1, WR2, WR4 and WR5, the drafting team reported that an update of the associated Table W-1 was underway by the Reliability Subcommittee.
The WSC agreed to expand the WECC-0100 drafting team to include the entire Reliability Subcommittee, and accept the drafting team’s recommendation that further drafting continue on remedial language for:
1) TPL-001-WECC-RBP-2.1. WR3;
2) Table W-1; and,
3) TPL-001-4, Requirements R5 and R6.
On December 5, 2013, the Board approved the decision to retire portions of the WECC TPL upon the Effective Date of the NERC TPL.
During June 2014, the Planning Coordinating Committee (PCC) conducted a straw poll concluding the most appropriate document categorization for this document should be that of a WECC Regional Criterion.
On June 24, 2014, the Board changed the designation of this document from that of a RBP to that of CRT.
Comments:
Xcel Energy:WECC-0100 Regional Criterion's Scope – Xcel Energy strongly recommends that the acceptable power oscillations damping criterion required as per 4.1.3 in TPL-001-4 should also be addressed within the scope of this project. In fact, we believe that it is as important, if not more important, to have a common criterion for acceptable power oscillations damping applicable in the WECC region, similar to the system planning performance criteria already included in the project's scope.
4.1.3. For planning events P1 through P7: Power oscillations shall exhibit acceptable damping as established by the Planning Coordinator and Transmission Planner.
Table W-1 Revision – We support the concept of having a revised version of Table W-1 within the scope of WECC-0100 project, as stated on pages 3 and 4 of the posted draft TPL-001-WECC-CRT-3. However, t appears that the expected quantitative content in any revised Table W-1 has been addressed in the form of requirements in the posted draft. Our preference is to have all the transmission system performance criteria captured in tabular form within a revised Table W-1, which may then be supplemented with requirements to the extent needed to support the tabular criteria.
(Page 3) Revision of Table W-1 is within the scope of this project. The drafting team understands that the Table is currently under review by the WECC Reliability Subcommittee (RS). The team will coordinate any changes with the RS.
(Page 4) The WSC agreed to expand the WECC-0100 drafting team to include the entire Reliability Subcommittee, and accept the drafting team's recommendation that further drafting continue on remedial language for:
1) TPL-001-WECC-RBP-2.1. WR3;
2) Table W-1; and,
3) TPL-001-4, Requirements R5 and R6.b
Responses:
- A damping criteria is also recommended in the scope of the document. [Xcel]
Scope DONE
During the drafting team’s meeting to respond to comments, Mr. Hari Singh explained his concerns regarding the scope of the document as it pertains to damping. Within WECC, the Peak Reliability Coordinator System Operating Limit methodology at Paragraph 37 includes a high level damping criteria. The drafting team agreed to include the substance of that paragraph into the criterion. A Rationale block and associated language were added as follows:
WR1.4Oscillations that do not show positive damping within a 30-second time frame shall be deemed undamped.
Rationale: For purposes of Requirement WR1.4, positive damping in stability analysis is demonstrated by showing that the amplitude of power angle or voltage magnitude oscillations after a minimum of 10 seconds is less than the initial post-contingency amplitude. In any case, results that do not show positive damping within a 30-second time frame shall be deemed undamped.
Footnote: This stipulation is not intended to require that transient stability simulations be run out to 30-seconds all the time in order to ensure the system is stable and positively damped. Shorter runs are permissible.
- It is recommended to retain a Table W-1 similar to the existing criteria. [Xcel]
WR1.4 Table W-1 DONE
Addressing the Table W-1 is within the scope of the WECC-0100 Standards Authorization Request (SAR). Once the Requirements are more fully developed the drafting team will revisit the need to retain, edit, or adopt the existing Table. The team is concerned that a static table may not meet the needs of mandating requirements. This item was listed as an action item in the December 16, 2014 meeting minutes and will be further discussed.
Requirement:
R1.Each Transmission Planner and Planning Coordinator shall use the following minimum criteria in its Planning Assessment: [Addressing NERC TPL R5, R6]
R1.1Steady-state voltages at all applicable Bulk-Electric System (BES) buses shall stay within each of the following limits [Addressing NERC TPL R5]:
1)95% to 105% of nominal for P0[1] event (system normal),
2)90% to 110% of nominal for P1-P7 events (contingency).
Comments:
BPA:- BPA believes the requirement should ensure applicable entities apply their established "internal" criterion rather than develop a one-size-fits-all criterion. Steady-state voltages are system dependent where low voltage is defined by minimum service to a utility's customers, and high voltage limits are driven by equipment issues.
- Regarding the proposed criterion posted, BPA believes the meaning of the term "nominal" should be clarified as individual entities use the term differently (e.g. base voltage in simulations, equipment nominal voltage specification, operating voltage schedule, etc.).
- Regarding the proposed criterion posted, BPA believes there is no technical justification for the high voltage for P0 events to be less than P1-P7 events. High voltage is driven by equipment issues, and voltage up to that specified for contingencies may also be acceptable for all lines in service.
Xcel Energy:
Please clarify that these are the default voltage limits for system normal and post-contingency system conditions, and an individual TP/PC may choose to use more restrictive voltage limits for its footprint. Note that the suggested approach is identical to what has been adopted by the Reliability Coordinator for implementing its SOL Methodology for Operations Horizon, and this approach lends itself well to be used in the Planning Horizon.
SRP:
R1.1 bases limits on "nominal" voltages. We recommend defining nominal voltage. If this is the system operating voltage then can each Transmission Planner define a unique range for each BES bus? If the nominal voltage for P0 started at 0.95 p.u. during P1 event and the nominal voltage went to 0.88 p.u, would that be a violation for R1.1 Part 2? This is less than 8% deviation but outside the bounds specified in Part 2.
Responses:
- Ensure each entity has a criteria for steady state voltage performance rather than develop a one size fits all approach. [BPA]
- Clarify the meaning of the term “nominal”. [BPA, SRP]
Requirement WR1 is designed to set the minimum threshold at which the Transmission Planner (TP) and the Planning Coordinator (PC) will examine their own systems. For purposes of examining their own systems, the TP and PC can use a more or less stringent set of criteria than stated in Requirement WR1; however, they may not impose a more stringent set of criteria on neighboring systems, and they must allow neighboring systems the same performance for a less stringent set of criteria.
To help clarify Requirement WR1, the following Rationale block has been added.
Rationale for Requirement WR1:
“Requirement WR1 recognizes that each system has its own unique characteristics that need to be addressed. Rather than lock each entity to a specific study parameter this Requirement sets a baseal study parameter coupled with a unique nominal value, established by the Transmission Planner and the Planning Coordinator, to be used in the absence of either a more stringent or less stringent study parameter.
In the context of this document the word “nominal” carries its common definition and is the base voltage used in the entity’s Planning Assessment model. This voltage will vary from entity to entity.
Requirement WR1 does not preclude an entity from using either a more stringent or less stringent criteria. However, when an entity uses a study criteria other than that required in requirement WR1, it must make available it’s criteria upon requestthe associated Planning Assessment showing the assumptions used (see later Requirement).”
This concept is further embellished in the Rationale box for Requirement WR1.2.
Use of the term “nominal”DONE
See Rationale box above.
- There is no technical justification for having high voltage criteria different for P0 than P1-P7. [BPA]
Technical Justification for High Voltage DONE
BPA suggests there is no technical justification for the high voltage for P0 events to be less than P1-P7 events. The drafting team recognizes that studied steady-state voltages will vary from one system to the next. For purposes of examining their own systems, the TP and PC can use a more or less stringent set of criteria than stated in Requirement WR1; however, they may not impose a more stringent set of criteria on neighboring systems, and they must allow neighboring systems the same performance for a less stringent set of criteria.Requirement WR1, subsets WR1.1.1 and 1.1.2 allow the studying entities to establish a unique nominal value that fits its specific system(s). In the context of Requirement WR1 “nominal” is uniquely determined by the steadying entity. The Applicability section also acknowledges that certain elements may be excluded from the WECC Criterion.
To address the issue, the drafting team has redrafted the Requirement as follows:
WR1. Each Transmission Planner and Planning Coordinator shall use the following baseal criteria in its Planning Assessment, unless otherwise specified in accordance with Requirements WR2 and WR3: [Addresses NERC TPL R5 and R6]
1.1.Steady-state voltages at all applicable Bulk-Electric System (BES) buses shall stay within each of the following limits:
1.1.1.95 percent to 110 percent of the nominal customer requirement.
1.1.2.90 percent to 110 percent of the nominal equipment protection level.
The drafting team further acknowledges that an exchange of this information is critical to establishing accurate models. To meet this need the drafting team has added the following Requirements and associated Rationale boxs.
WR2. Each Transmission Planner and Planning Coordinator that uses more stringent criteria in its Planning Assessment than that stated in Requirement WR1 shall apply that criteria solely to its own system.
Rationale for WR2: The purpose of this Requirement is to clarify that an entity may apply a more stringent criterion to its own system; however, it may not impose that more stringent criterion to any other system.
WR3. Each Transmission Planner and Planning Coordinator that uses less stringent criteria in its Planning Assessment than that stated in Requirement WR1 shall allow other Transmission Planners and Planning Coordinators to have the same impact on that part of the system for the same planning events.
WR43. Each Transmission Planner and Planning Coordinator that uses study criteria different from the baseal criteria in Requirement WR1 shall make its criteria Planning Assessment available upon request.
- Clarify these are default criteria and an entity can have more restrictive criteria. [Xcel]
Requirement WR1.1 DONE
Xcel requests: Cclarification that Requirement WR1.1 represents fault voltage limits for system normal and post-contingency system conditions, and those individual TP/PCs may choose to use more restrictive voltage limits for its footprint.
The drafting team has added a number of Rationale Blocks to the document to further clarify the intent of the Requirements and the Requirement subsets.
- Clarify whether delta V from 0.95 to 0.88 is a violation even though it may meet WR1.2. [SRP]
Violations
SRP asks that where the nominal voltage for P0 started at 0.95 p.u. during P1 event and the nominal voltage went to 0.88 p.u, would that be a violation for Requirement WR1.1, Part 2? The intent of the criteria is that Transmission Planners and Planning Coordinators meet all requirements. Regarding specific examples, that is a question of interpretation which is a compliance issue. The Standard Drafting Team can only respond to comments related to development of the criteria itself.
PENDING
Requirement:
R1.2Post-Contingency steady-state voltage deviation at each applicable BES bus serving load (having nointermediate connection) shall notresult in voltage deviation exceeding eight percent for P1 events. [Addressing NERC TPL R5]
Comments:
BPA:- BPA suggests Requirement R1.2 be clarified that shunt reactive devices (added to support and control voltages) are assumed to be able to be switched to maintain an acceptable post-contingency steady-state voltage deviation.
Xcel Energy:
No technical justification has been provided to support the 8% limit and discontinue usage of the existing Table W-1 Post-Transient Voltage Deviation limits of 5% for single (Cat-B or event P1) contingencies and 10% for multiple (Cat-C or events P2-P7) contingencies. Absent a technical justification for change, the existing Table W-1 Post-Transient Voltage Deviation limits must be retained.
SRP:
R1.2: Are there any requirements for voltage deviation? Suppose the nominal system voltage was 0.96 p.u. and with P2 events the nominal went to 0.89 p.u. even though the deviation is not 8% or 10%, would this violate R1.1 Part 2?
Responses:
- Clarify shunt reactive devices are assumed to be switched to meet post-contingency voltage deviation. [BPA]
Requirement WR1.2: Post-contingency Steady-State Voltage Deviation DONE
BPA suggests clarification of Requirement WR1.2 to show that shunt reactive devices are assumed to be able to be switched to maintain an acceptable post-contingency steady-state voltage deviation.
The drafting team does not believe that manual switching should be assumed; rather, the existing practice of assuming automatic switching should be retained. Requirement WR1.2 has been redrafted as follows:
WR1.2Post-Contingency steady-state low voltage deviation at each applicable BES bus serving load (having no intermediate connection) shall not exceed eight percent for P1 events. [Addressing TPL R5]
The WR1.2 Rationale box has been elaborated as follows:
“Rationale for Requirement WR1.2:
Requirement WR1.2 establishes a reasonable target that could be met by each entity without incurring costs that would outweigh the benefits. Many legacy systems were not designed to meet a more stringent threshold. The eight percent target of Requirement WR1.2 is established not by a technical study; rather, it is established based on sound engineering judgment. Further, certain entities are bound by state tariffs that establish the percentage rate specifically at eight percent.
By default, only automatic post-contingency actions including capacity or reactor switching are considered when calculating voltage deviation.
With that said, it is recognized that each system has its own unique characteristics that need to be addressed. For purposes of examining their own systems, the TP and PC can use a more or less stringent set of criteria than stated in Requirement WR1; however, they may not impose a more stringent set of criteria on neighboring systems, and they must allow neighboring systems the same performance for a less stringent set of criteria. The drafting team has added a number of Rationale Blocks to the document to further clarify the intent of the Requirements and the Requirement subsets. Where the Transmission Planner or the Planning Coordinator apply less stringent criteria when studying their own systems, the less stringent criteria would be permissible so long as other Transmission Planners and Planning Coordinators were also allowed to apply the same less stringent criteria to their own systems. For example, if an entity applied manual capacitor or reactor switching to its own system the same criteria would be allowed for the systems of others. By contrast, where the Transmission Planner or the Planning Coordinator applies more stringent criteria to their own systems, that Transmission Planner or Planning Coordinator would not be allowed to impose the more stringent criteria on any system other than its own.”