FERC Order No. 881: Managing Transmission Line Ratings (MTLR)

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Last update: 12/10/2024

Below, affected ISO New England (ISO-NE) participants can learn more about changes to existing systems and procedures related to the Managing Transmission Line Ratings (MTLR) project. This project is one of several that ISO-NE has undertaken, in collaboration with stakeholders, for the continued development of the region’s wholesale electricity markets.

See the Participant Readiness Project Outlook for a summary of specifically affected participants and systems for this and other major projects. To receive announcements about readiness outlook summaries, project pages, and training, please subscribe to the Participant Readiness and ISO Training mailing lists in Ask ISO. Refer to the How to Manage Your Mailing Lists article for instructions.

Project Overview
Required Participant Actions
Participant Training Opportunities
Technical Documentation, Rules, and Procedures
Project Development Materials

Project Overview

The Federal Energy Regulatory Commission (FERC) issued Order Nos. 881 and 881-A, Managing Transmission Line Ratings, to improve the accuracy and transparency of transmission line ratings, to ensure just and reasonable wholesale rates, and to better align the transmission grid with actual operating conditions.

Transmission line ratings are the maximum energy transfer capability of a transmission line, considering the technical limitations on conductors and relevant transmission equipment. These ratings are used to make planning and operations decisions during normal and emergency conditions.

Weather conditions may affect the transfer capability of a transmission line, and incorporating ambient adjusted ratings (AARs) will account for the effects of ambient temperature and solar heating on the transfer capability of the transmission line. The use of AARs in the Day-Ahead Market (DAM) and Real-Time Market (RTM) will allow the energy, ancillary services, and transmission service wholesale rates to more accurately reflect the cost of delivering wholesale energy to transmission customers.

Order Nos. 881 and 881-A establish the following requirements:

The use of AARs in the DAM and RTM
At least four seasonal line ratings for longer-term transmission service requests
Unique emergency ratings
Electronic updates of ratings data on at least an hourly basis

In order to collect, utilize, and share AAR data, ISO New England will introduce two new applications.

The operational Limit Exchange Portal (LEP) will be used to submit required equipment information, such as hourly-forecasted AARs, nominal ratings sets, seasonal ratings sets, temporary ratings, and AAR exemptions via an application programming interface (API). The LEP will be used to exchange forecasted ratings with affected market participants and independent system operators (ISOs).
The historical LEP will be used to provide a five-year history of equipment information and local transmission service data to interested parties.

Additionally, a LEP user interface will be available for local transmission owners to add, edit, and retire local transmission equipment.

With the introduction of the LEP, default seasonal ratings in the NX application will be removed and new fields will be added.

Implementation date: July 12, 2025

Required Participant Actions

Affected market participants are required to take specific steps or adapt to changes in ISO-NE systems as described below. Participants should be mindful of additional time-bound items, some of which may require participants to take specific steps or adapt to changes in ISO-NE systems both before and after the project implementation date.

TIMING OR DEADLINE	SYSTEM	ACTION OR EVENT
Beginning July 31, 2024	N/A	Participants begin their selection of a weather forecast vendor to provide the weather data component of their temperature-based line ratings.
Limit Exchange Portal (LEP) Sandbox Roles: September 24, 2024 LEP Production Roles: July 12, 2025	Customer and Asset Management System (CAMS)	Security administrators (SAs) assign new LEP sandbox or production roles for the operational user interface. Power System Limits Exchange Portal Sandbox / Submitter Power System Limits Exchange Portal Sandbox / Viewer Power System Limits Exchange Portal / Submitter Power System Limits Exchange Portal / Viewer
Sandbox (1^st release): October 18, 2024 Sandbox (2^nd release): December 4, 2024 Production: July 12, 2025	LEP Sandbox and Production (operational)	A representational state transfer application programming interface (RESTful API) will be provided to submit new ratings to the operational LEP in the 1^st sandbox release. The local transmission functionality will be available in the 2^nd sandbox release. eFTR and NX users who are consumers of PSSe and ratings data should request access to the LEP from their SAs.
Sandbox: April 30, 2025 Production: July 12, 2025	NX912D Application Sandbox and Production	Add new flags and fields to the NX-9 form: Ratings to be Provided Via Telemetry flag Conditional Ratings flags Nominal Ratings fields Remove seasonal ratings management.
Sandbox: March 31, 2025 Production: July 12, 2025	LEP Sandbox and Production (historical)	A RESTful API will be provided to query historical ratings. eFTR and NX users who are consumers of PSSe and ratings data should request access to the LEP from their SAs.

Participant Training Opportunities

ISO New England and GE Grid Solutions may offer online or classroom-based training, information sessions, and other opportunities for affected customers to learn about changes and ask questions in advance of project implementation.

DATE	EVENT AND SUPPORTING MATERIALS
Recurring, beginning June 26, 2024	FERC Order No. 881 Managing Transmission Line Ratings Implementation Workshops for designated technical contacts to discuss Limit Exchange Portal (LEP) technical design and NX application changes. Meeting recordings are posted as they become available. Click here for the meeting link to join the sessions at 3:00 ET below: June 26, 2024, meeting recording and presentation July 31, 2024, meeting recording and presentation August 28, 2024, cancelled September 25,2024 (no recording), presentation October 30, 2024, meeting recording and presentation November 20, 2024, cancelled No December Meeting January 29, 2025 February 26, 2025 March 26, 2025 April 30, 2025 May 28, 2025 June 25, 2025
February 21, 2024	Introduction to Transmission Ratings and Operating Limits Information Exchange (TROLIE)—A technical introduction to the communication specification for reliability coordinators and transmission owners presented by GE Grid Solutions in partnership with The Linux Foundation and the Midcontinent Independent System Operator (MISO).
November 20, 2024	A Lap Around Trolie 1.0—In this webinar, the TROLIE maintainers will explore these use cases and highlight how the TROLIE OpenAPI specification addresses them. Attendees will gain insights into the concepts that the TROLIE project identified when articulating solutions to the 881 use cases, as well as how to make effective use of the project documentation and the specification itself. The presentation will focus on ensuring the audience is prepared to implement their respective interoperability use cases. Accordingly, this will be a fast-paced, in-depth tour of all that the project has produced as it nears completion.

Technical Documentation, Rules, and Procedures

Market participants affected by the project should consult the following documents for specific instructions on completing related tasks or processes and helpful answers to frequently asked questions.

Technical Specifications and Documentation

DOCUMENT	NOTES (if necessary)
Limit Exchange Portal (LEP)	Application programming interface (API) documentation and user guide to be provided.
Trolie JAVA Client Software Development Kit	Trolie client library for TOs to invoke the LEP API.
Customer Asset Management System (CAMS) Application Group Roles	Updated to include the LEP production and sandbox application and role descriptions.
Transmission Planning Technical Guides	To be updated.

Rules and Procedures

DOCUMENT	NOTES (IF NECESSARY)
OP-16—Transmission System Data	Appendix A—Explanation of Terms and Instructions for Data Preparation of NX9-A Appendix B—Explanation of Terms and Instructions for Data Preparation of NX9-B Appendix C—Explanation of Terms and Instructions for Data Preparation of NX9-C Appendix D—Explanation of Terms and Instructions for Data Preparation of NX-9D Appendix E—Annual Certification Appendix G—Explanation of Terms and Instructions for Data Preparation of NX-9 Appendix H—Explanation of Terms and Instructions for Data Preparation of NX-9H Appendix I—Explanation of Terms and Instructions for Data Preparation of NX-9 (Other Equipment)
OP-18—Metering and Telemetering Criteria
OP-19—Transmission Operations
M/LCC7—Processing Outage Applications
M/LCC13—ISO and LCC Communication Practices
M/LCC15—System Operating Limits Methodology
Planning Procedure No. 7 (PP7)—Procedures for Determining and Implementing Transmission Facility Ratings in New England

Project Development Materials

RM20-16-000 Order No. 881 Managing Transmission Line Ratings
FERC News Release: FERC Rule to Improve Transmission Line Ratings Will Help Lower Transmission Costs
Order No. 881 NEPOOL committee presentations and FERC filings and orders NEPOOL technical committee materials for participants and stakeholders, related FERC documentation.