TLR Investigation Procedure
The NERC Operating Committee retired the TLR Investigation Procedure effective July 1, 2011.
To develop a procedure for use by the NERC/NAERO Compliance Program when investigating transmission loading relief events carried out by the NERC Reliability Authorities (RAs) in North America in accordance with Policy 9. These investigations will be conducted to identify lessons learned, reliability impacts, and fairness in implementation. The purpose of the investigations will not be to measure compliance with open access tariffs as filed by any party with their regulators.
Initiation of Investigations
Investigations may be initiated via several different methods. These are as follows:  
  1. Routine Investigations
    Routine investigations will be initiated when:
    1. Any affected RA reports the lack of a timely/clear response from the implementing RA, or
    2. TLR Level 5 is initiated.
  2. Requested Investigations
  3. Requested investigations will be initiated:
    1. For any single TLR event, when requested by three entities (CA, PSE, RA, TP),
    2. For TLR events recurring on the same flowgate and requested by three entities, not necessarily from the same TLR event, or
    3. When the Reliability Authority did not receive the relief expected and requests an investigation.

Requests for investigation must be received within 30 days of the TLR event.

The NERC director of Compliance will review the request for validity and, if appropriate, will initiate the initial investigation. In the event the parties involved are denied an investigation by the NERC director of Compliance, they may appeal to the president of NERC and request that an investigation be carried out.
Further, a TLR investigation may be initiated by the NERC director of Compliance: 
  1. When TLR 3 or higher is called three times or more, within a seven-day period, on the same flowgate, or
  2. When TLR 2 is called six times or more, within a 30-day period, on the same flowgate, or
  3. For any reason, as deemed by the Operating Reliability Subcommittee (ORS) Chair, the Reliability Authority Working Group Chair (RAWG), or NERC director of Compliance.
Not all TLR events that meet the first two items above will be investigated. For example, if a recurring problem exists and the flowgate and associated TLR activity have been reviewed, it is not necessary to complete another review, unless specifically requested.
Measuring Processes
The measuring process will be divided into two separate areas. The first will be a high-level reporting and an initial investigation. This investigation must be initiated within 30 days of the TLR event. The purpose of this effort will be to provide some insights and immediate lessons learned. Should such an effort reveal the need for a more thorough investigation, or at the request of the parties requesting the investigation, a second, more detailed investigation will be initiated. This effort may take several weeks to months to complete. Further, spot reviews may be requested from time to time.
Initial Investigation
Once a TLR has been selected for investigation, the first step of the process will be to begin an initial investigation with the Reliability Authority who initiated the TLR event. The NERC director of Compliance will request a report from the Reliability Authority who initiated the TLR event. At a minimum, this report must include the following information:  
  • Description of purpose or cause of hold/curtailment;
  • Facility or flowgate limitations and flows at the time the TLR was initiated;
  • TLR levels, timing, and relief requested amounts;
  • Transmission and generation outages or changes from prediction that may have contributed;
  • Procedures implemented prior to hold/curtailment;
  • List of known transactions not in the IDC with Transaction Contribution Factors greater than the curtailment threshold and actions taken to curtail such transactions;
  • Excerpts from the RA Operations Log containing information relevant to the TLR event;
  • Flowgate limitations as identified by security analysis processes conducted by the Reliability Authority for the day prior to the TLR event;
  • State Estimator snapshots and security analysis, including any contingency analysis or stability analysis, along with any other recorded data indicating need for TLR;
  • ATC limitations before, during, and after the TLR event;
  • Description of actions taken to avoid future hold/curtailments;
  • Provide IDC-generated Congestion Management Reports showing transaction curtailment list and Control Area NNL (network and native load) curtailment responsibility; and
  • Redispatch actions taken.

The initial investigation shall compare all transaction curtailment lists as generated by the IDC with the list of transactions flowing as determined by the IDC (Whole Transaction Lists) both before and after curtailment. The reasons for any transactions that were excluded from curtailment shall be provided. For those transactions not curtailed, the Reliability Authority will identify those entities and any affiliation with said entities.

The Reliability Authority who initiated the TLR will prepare a report addressing each of the above points within 20 working days of the request. The report will be provided to the NERC director of Compliance and the Chairs of the ORS and RAWG. NERC will also post the report on the NERC website for public dissemination. The NERC director of Compliance, the NERC ORS Chair, the NERC RAWG Chair, and any parties who requested the investigation will review the report and determine if a more detailed investigation is warranted. Results will also be reported to the NERC Operating Committee at the next regularly scheduled meeting.
The RA shall retain all data related to the TLR event for six months following:  
  1. Posting of the initial investigation report, or
  2. Completion of the detailed investigation report, if requested.
Detailed Investigation

Once the initial investigation has been completed, it may be necessary to complete a more detailed audit of the TLR event. This would come at the request of the NERC director of Compliance, the original parties who requested the audit, the NERC ORS or RAWG Chairs, or the NERC Operating Committee Chair. Any such request must be made within 30 days subsequent to the posting of the report resulting from the initial investigation. The purpose of this investigation will be to review in detail all aspects of the TLR process from beginning to end. A team comprised of one person from compliance staff of an unaffected Region, one unaffected Reliability Authority, and one person from NERC compliance staff will carry out this detailed investigation. Additionally, at the request of the Operating Committee Chair, it may be necessary to secure the services of an independent auditor to carry out such an investigation. Such a complete investigation will require significant resources and time to complete. In such an investigation, it is not the intent to collect the same information as included in the initial report. There may be a need for additional data and information, as well as a site visit. However, all aspects of the initial report will be reviewed. Additionally, staff members will:  

  • Review the stated purpose or cause of hold/curtailment and the validity of purpose;
  • Review facility/flowgate limitations for accuracy and actual flows;
  • Investigate the system topology model utilized and compare to the actual system topology for accuracy;
  • Review SDX data and actual outages to determine if all relevant outages were submitted in order to produce accurate IDC results;
  • Review other options or procedures considered and any others that may have been available before or during to avoid hold/curtailment;
  • Check Reliability Authority Operational Logs for the period for consistency with stated actions;
  • Review previous day system studies and any current day system studies for accuracy with known outages, limitations, generation patterns, and load expectations;
  • Review any state estimator output, loading trends, etc., to determine if earlier corrective action was warranted;
  • Review Transaction Curtailment Lists generated by the IDC for accuracy of the data and the calculations performed;
  • Survey Control Areas for the actual time of curtailment of transactions and compare to Reliability Authority requests;
  • Review whole transaction lists from the IDC both before and after curtailment and compare to curtailment list. Also, determine if new transactions were initiated in restricted directions;
  • Collect actual schedules from sink Control Areas and compare to whole transaction lists from the IDC to determine if all schedules were entered and, hence, subject to curtailment;
  • Review transaction list from the IDC indicating upcoming higher priority transactions and actions taken to adjust current schedules;
  • Review RAIS system messages for consistency and other methods of communication;
  • Review TLR levels, timing, and relief-requested amounts;
  • Review ATC limitations before, during, and after the TLR event and OASIS reservations related to the flowgate;
  • Review and analyze actions taken to avoid future hold/curtailments for expected effectiveness; and 
  • Identify of any NERC policies violated.
During the detailed investigation process, there will be several steps necessary to insure accuracy. These include:  
  1. Review of the initial report and identification of key issues to be investigated;
  2. Identification of additional information required (This should be completed as quickly as possible to allow reasonable time for the parties involved to respond and to include the data in the report.);
  3. Collection of additional data and information (Reliability Authorities and other parties are to provide items requested within 10 business days of the request.);
  4. Initial review and findings developed by the review team;
  5. Review of findings of fact with Reliability Authority who initiated the TLR;
  6. Development of findings and recommendation of the investigation;
  7. Development and submission of final report;
  8. Appeals by the affected Reliability Authority (if in disagreement with findings); and  
  9. Possible dispute resolution.
Every attempt should be made to complete detailed investigations within a 60-day period. However, the investigation should not be limited to that period. The focus should be on thorough and accurate results.
The final report will be posted on the NERC website and presented to the Reliability Authority Working Group, the Operating Reliability Subcommittee, and the Operating Committee.
Identification of Confidential Data or Information
During the course of the initial or detailed investigation, Reliability Authorities are to fully disclose all information regarding the TLR event. In the event that there is market sensitive information included in the report developed for the initial investigation or in the report for any detailed investigations, that data or information is to be marked as “confidential” and will be omitted from the report as posted on the NERC website.
Version 2 - Approved by the NERC Operating Committee on July 18, 2002
Version 2 – Retired by the NERC Operating Committee effective July 1, 2011