Skip Links

Transmission Losses

Forecasting and Planning

In the Decision and Order on the IESO’s 2018 Expenditures, Revenue Requirement, and Fees submission (EB-2018-0143, “2018 Revenue Requirement”), the Ontario Energy Board (OEB) accepted the Package Settlement as agreed to between the IESO and participating intervenors. The Package Settlement included a condition that the IESO engage with stakeholders regarding the IESO's transmission losses work to explore cost effective opportunities for line loss reduction with Hydro One.

To satisfy this condition, the IESO will lead a formal stakeholder engagement on transmission system losses. As part of this engagement, the IESO, with Hydro One’s assistance, will prepare supporting materials building upon the public information session conducted in September 2019 that informed stakeholders on how transmission system losses are considered during planning of the transmission system in Ontario.

Through this engagement, the IESO will seek feedback from stakeholders on:

  • Opportunities to cost-effectively reduce transmission losses, including through improved processes, cost-benefit analysis methodologies, documentation, and reporting
  • The preparation of the final report
  • The need for, and the incremental value of, retaining independent, third expertise to review these processes and identify further areas for improvement

Additional details on the IESO’s plans to engage with stakeholders can be found in the engagement plan. All comments and enquiries on this engagement can be directed to

Anticipated timing for this engagement is presented below.

Related Information

  • September 6 Public Information Session presentation
  • Power Advisory feedback from September 6 Public Information Session
  • IESO response to Power Advisory feedback

Documents referenced on this page, but not posted, can be obtained by contacting with a link to the web page that lists the document and advise whether it needs to be provided in an accessible format. Please allow a minimum of one business day for a response.

Schedule of Activities

Timing Materials Expected Actions

December 7, 2023

Final Engagement Summary Report


June 2023

Transmission System Losses: Evaluation Guideline

August 13, 2021

Deadline for stakeholder feedback on the draft guideline.


July 22, 2021

Draft report published for stakeholder review and comment:

Transmission Planning Guideline - Consideration of Losses

Feedback form


March 31, 2021

Transmission Losses Stakeholder Engagement Update


October 22, 2020

IESO is seeking feedback from stakeholders on the materials presented at the September 30th webinar

IESO Response to Stakeholder Feedback


September 30, 2020

Engagement Webinar

This webinar will review IESO and Hydro One's practices regarding how transmission losses are considered in planning and operation of the system, a comparison of these practices to those used in other jurisdictions, and seek stakeholder feedback on potential improvements to these practices.

Recorded Presentation

This webinar is being presented during the IESO's September stakeholder engagement sessions, see full agenda for more information.

Registration List

Documents prior to 2020

Documents are available upon request. Email with specific instructions and advise if an accessible format is needed.


September 6, 2019

Public Information Session #1

Purpose and timeline for these sessions, an explanation of transmission losses, and the accountabilities between the IESO and transmitters

Stakeholder Feedback