WECC-0100 TPL-001-WECC-CRT-3 - Comment Summary - Chuck Matthews 12-12-2014 for 1-6-2015

WECC-0100 TPL-001-WECC-CRT-3 - Comment Summary - Chuck Matthews 12-12-2014 for 1-6-2015

Transmission System Planning Performance

WECC Regional Criterion


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.

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

1.Address damping criteria in TPL-001-4 R4.1.3.

2.Retain a Table W-1 to show requirements more concisely.
B. Requirements and Measures

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).

  1. 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.
  2. 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.).
  3. 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.
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.
  1. Clarify what nominal means.
  2. Clarify can have criteria different than this.
  3. Clarify/justify high voltage if different for ALIS.
  4. Research RC SOL methodology approach.

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]

  1. 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.
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?
  1. Clarify shunt reactive devices used to meet voltage deviation.
  2. Provide technical justification.
  3. Clarify the old 10% voltage deviation.

Action item –Research technical justification.

R1.3Voltage stability is identified by maintaining positive reactive power margin demonstrated by the following criteria: [TPL R6]

1)All P0-P1 events solve at a minimum of 105% of transfer path flow or forecasted peak load,

2) All P2-P7 events solve at a minimum of 102.5% of transfer path flow or forecasted peak load.

  1. P2-P7 events should be clarified so the real power margin 1) applies after load shedding for events where load shedding occurs as a result of the contingency; and 2) does not apply to events where non-consequential load loss is allowed.

Xcel Energy:
This appears to be essentially the same as the existing WR3, albeit stated somewhat differently. However, the re-stated criteria in items (1) and (2) need a better description. For example, it is unclear what is meant by "solve" in this context – does it pertain to steady-state power flow simulation or dynamic/transient stability time-progression simulation? How does this voltage stability criteria correlate to the existing WECC Voltage Stability Methodology document? Lastly, since voltage instability is listed as one of three instability modes within R6 of NERC TPL-001-4, shouldn't R1.3 be included under R2 which addresses the remaining two instability modes of Cascading and uncontrolled islanding?
R1.3: We recommend separating out transfer path flow and forecasted peak load into two separate items. Please clarify what the 105% and 102.5% applies to. We suggest “Solve with a pre-contingency flow with at least 105% of transfer path flow” and “Solve with a pre-contingency load with at least 105% of forecasted peak load”.
  1. Clarify how margin relates to events allowing loss of load or that include load shedding.
  2. Clarify “solve”.
  3. Consider including R1.3 under R2.
  4. Separate out transfer paths versus peak load and clarify requirements.

R1.4Transient voltage response shall be verified by demonstrating that for all P1-P7 category events, the transient voltage response at applicable BES buses shall recover to 80% of pre-contingency voltage within 10 seconds of the initiating event.

  1. BPA proposes the term "Transient voltage response" is changed to "Transient stability voltage response". "Transient voltage response" can imply a shorter time period that includes switching transients (milliseconds versus cycles).
  2. For P1 contingencies with 1-phase or no-fault, the primary objective should be continuity of service to loads. For other criterion contingencies, the primary objective should be integrity of the grid including generators low "Voltage ride-through" capabilities.
  3. BPA believes simulations should be conducted to better refine the voltage recovery parameters in the requirement. Simulations should include several scenarios, stressed conditions, and composite load models to help gauge the minimum level of acceptable system performance.

Xcel Energy:
Again, no technical justification is provided for discontinuing usage of the existing Table W-1 Transient Voltage Dip magnitude-duration limits for the Cat-B (event P1) and the Cat-C (events P2-P7) contingencies. Therefore, it is hard to appreciate why the proposed transient voltage response/recovery magnitude-duration limit uses 80% voltage magnitude consistent with the existing Table W-1 magnitude limit, but allows recovery duration of 10 seconds (i.e. 600 cycles) which is significantly longer (15 times) than the existing 40 cycles duration in Table W-1. Further, without any technical justification, it is unclear why it is acceptable to have a voltage recovery duration at load buses that is 3.33 times longer than the 3 seconds allowed at generator buses per the PRC-024 Attachment 2 Voltage Ride-Through Time Duration Curve?
For the new standard's R1.4 requirement: The recovery bvoltage used to be 80% for no more than 40 cycles (i.e. 2/3 of a second) instead of the proposed 80% for 600 cycles (i.e., 10 seconds). Do we have any simulations or real time disturbance data demonstrating stable system wide operation when the voltage is that low (0.8 per unit) for that long (10 seconds) ? If not, shouldn't the group developing this new standard generate some simulations demonstrating this, before we ask the members to approve such a requirement?
R1.4: Are there different provisions for three phase faults versus single phase faults? Will this criteria be applicable to Path Rating studies using the stress cases?
We have some seriousreservations onR1.4 and its implications. This seems to be a very simplistic view of Transient voltage response, and does not consider the impact that transient low voltages will have on the new composite load model (not to mention generators) and its impact on system response. Such a lenient requirement opens the doors to system responses that would not have been considered acceptable in the past and that will elevate the exposure to unnecessary operational risks and reduction in System reliability.
Voltage recovery to 80% after 10 seconds? There might not be a system (in real life) to recover to at that point.
I think we should also retain the PRC-024-1 curve at the end of the document (this is part of the Guidance Section, yet to be finalized.)
In the meantime a simple example, that probably requires no validation and I think may be considered a real problem, is the scenario where you allow voltages to stay very low for say, eight or less seconds, and then have them recover to 80% within 10secs. If such a voltage excursion results in tripping of generators in a neighboring area how can you justify that this be considered acceptable response? A similar scenario may result in loss of an inordinate amount of load. I am sure the lawyers will be knocking at your door pretty soon.
You would meet your R1.4 criteria, but is this really the type of performance that we want to experience in our systems?
It is not unrealistic to think up a scenario where the voltage depression and duration (within the 80% in 10 seconds criteria) might not be sufficient to cause cascading, instability and uncontrolled separation, but enough for a few units to trip (inside or outside the control area)..
Would this be a violation of TPL-001-4, I think not. Thus relying on TPL-001-4 to screen out forthis performance will probably not work .
Would we want to consider this performance acceptable? I hope not.
Note that a similar logic could also be applied to loads.
  1. Consider differentiating performance for 1-phase versus 3-phase faults for P1 events.
  2. Conduct simulations to test criteria and refine parameters.
  3. Provide technical justification if changing from existing Vdip criteria.
  4. Clarify difference between Vdip and V recovery if needed.
  5. Consider retaining PRC-024 curve, at least for generators.

Action item - Completion of white paper that includes research and simulations.

R2.Each Transmission Planner and Planning Coordinator shall investigate the potential for Cascading and uncontrolled islanding, if one or more of the following are observed in its Planning Assessment studies: [TPL R6]

  • Thermal overload on a Facility exceeds the phase protective relay settings described in NERC PRC-023-2 Transmission Relay Loadability,and trips.
  • Any single generator pulls out of synchronism and trips.
  • The transient voltage response at any BES bus is outside of the voltage ride-through criteria defined in Requirement R1.3.2 of this document, after a delayed fault clearing disturbance.

  1. First bullet: Reference to NERC PRC-023-2 – BPA recommends this be revised to NERC PRC-023-3 as version 2 was retired October 1, 2014.
  2. Third bullet: BPA requests clarification of the reference to R1.3.2. The requirement seems to refer to transient stability requirements in R1.4.
  3. BPA believes references to "TPL" in the document should be "TPL-001-4" or referenced by a footnote as "NERC Standard TPL-001-4".
  4. BPA suggests referencing Attachment 2 from PRC-024-1 as is not referenced in the document other than "Voltage ride through" criteria as defined. Additionally, in PRC-024-1, there is a list of "Voltage Ride-Through Curve Clarifications" (1-5) that are not included in the document - - should they be?​​

Xcel Energy:
We agree with the first bullet (thermal overload criterion) and the third bullet (unacceptable transient voltage response) as the potential precursors of uncontrolled system instability but cannot appreciate how the second bullet's criterion of one generator pulling out of synchronism can possibly lead to system-wide instability. Again, technical justifications for each of the three bullets would be very helpful.
R2, bullet 1: Does this apply only to lines/transformers identified in PRC-023-3 analysis, or should this apply to all BES lines/transformers?
R2, bullet 3: Please clarify voltage ride-through.
  1. Need to better quantify “single generator pulls out of synchronism”.
  2. Provide technical justification for each bullet.
  3. Clarify what “PRC-023” reference is referring to such as all BES circuits where PRC-023 is applied.
  4. Clarify voltage ride-through.

Action item – Research technical justification.

Developed as WECC-0100Page 1

[1] Those points identified as “P” in this document refer directly to the NERC Standard TPL-001-4, Transmission System Planning Performance Requirements, Table-1 Steady State and Stability Performance Planning Events.