Section 503.6 and Section 503.18 Amendments

Important Dates & Materials

December 17, 2025 | Stakeholder Feedback due

November 26, 2025 | Letter of Notice and related materials posted

Background and Purpose

Section 503.6

On July 31, 2025, the AESO received an ISO Rule Proposal from TransAlta to amend Section 503.6, proposing to amend subsection 6 which has an incorrect reference. TransAlta identified that subsection 6 incorrectly references Section 503.19 and has proposed that the subsection should be corrected to reference Section 503.18, as follows:

6 The operator must, subject to Section 503.18 of the ISO rules, Operation and Maintenance of Facilities, operate the generating unit, aggregated facility, or energy storage resource with the governor system in service, in droop mode, and free to respond to frequency changes while:

(a) supplying active power to the interconnected electric system; or

(b) providing an ancillary service that requires a response to frequency changes.

The AESO has identified that the reference to Section 503.19 in subsection 6 is an error and agrees with TransAlta’s Rule Proposal that the reference should be corrected.

Section 503.18

On November 7, 2024, the AESO received an ISO Rule Proposal from Enfinite to amend Section 503.18, proposing to amend subsection 3(2) which has an errant omission. Enfinite identified that subsection 3(2) is missing subsection (b) and has proposed the following language be added, which carries over from the predecessor Section 502.6 Generating Unit Operating Requirements:

(2) The legal owner must:

(a) submit the operating data requested by the ISO, if available, no later than 5 business days after receipt of the notices set out in subsection 3(1); or

(b) if the operating data requested by the ISO is not available, advise the ISO in writing no later than 5 business days after receipt of the notice set out in subsection 3(1).

The AESO intended to transition subsection 7(1)-7(2) of Section 502.6 to subsection 3(1)-3(2) during the development of Division 503, which is evidenced by the Table of Concordance for the Transition from Division 502 to Division 503 of the ISO rules. The AESO agrees with Enfinite’s Rule Proposal that subsection 3(2) should be amended to correct the omission.

The Rule Proposals can be found on the ISO Rule Proposal page on AESO.ca.

Pursuant to Alberta Utilities Commission Rule 017, Procedures and Process for Development of ISO Rules and Filing of ISO Rules with the Alberta Utilities Commission, the AESO is providing notice and seeking feedback from the Stakeholders on a proposed amendment to Section 503.18.


Important Dates & Materials

December 17, 2025 | Stakeholder Feedback due

November 26, 2025 | Letter of Notice and related materials posted

Background and Purpose

Section 503.6

On July 31, 2025, the AESO received an ISO Rule Proposal from TransAlta to amend Section 503.6, proposing to amend subsection 6 which has an incorrect reference. TransAlta identified that subsection 6 incorrectly references Section 503.19 and has proposed that the subsection should be corrected to reference Section 503.18, as follows:

6 The operator must, subject to Section 503.18 of the ISO rules, Operation and Maintenance of Facilities, operate the generating unit, aggregated facility, or energy storage resource with the governor system in service, in droop mode, and free to respond to frequency changes while:

(a) supplying active power to the interconnected electric system; or

(b) providing an ancillary service that requires a response to frequency changes.

The AESO has identified that the reference to Section 503.19 in subsection 6 is an error and agrees with TransAlta’s Rule Proposal that the reference should be corrected.

Section 503.18

On November 7, 2024, the AESO received an ISO Rule Proposal from Enfinite to amend Section 503.18, proposing to amend subsection 3(2) which has an errant omission. Enfinite identified that subsection 3(2) is missing subsection (b) and has proposed the following language be added, which carries over from the predecessor Section 502.6 Generating Unit Operating Requirements:

(2) The legal owner must:

(a) submit the operating data requested by the ISO, if available, no later than 5 business days after receipt of the notices set out in subsection 3(1); or

(b) if the operating data requested by the ISO is not available, advise the ISO in writing no later than 5 business days after receipt of the notice set out in subsection 3(1).

The AESO intended to transition subsection 7(1)-7(2) of Section 502.6 to subsection 3(1)-3(2) during the development of Division 503, which is evidenced by the Table of Concordance for the Transition from Division 502 to Division 503 of the ISO rules. The AESO agrees with Enfinite’s Rule Proposal that subsection 3(2) should be amended to correct the omission.

The Rule Proposals can be found on the ISO Rule Proposal page on AESO.ca.

Pursuant to Alberta Utilities Commission Rule 017, Procedures and Process for Development of ISO Rules and Filing of ISO Rules with the Alberta Utilities Commission, the AESO is providing notice and seeking feedback from the Stakeholders on a proposed amendment to Section 503.18.


  • Written Consultation | November 26 - December 17, 2025

    Purpose 

    Pursuant to Alberta Utilities Commission Rule 017, Procedures and Process for Development of ISO Rules and Filing of ISO Rules with the Alberta Utilities Commission (AUC Rule 017), the AESO is providing notice and seeking feedback from stakeholders on proposed amendments to Section 503.6, Frequency & Speed Governing (Section 503.6) and Section 503.18, Operation and Maintenance of Facilities (Section 503.18) of the ISO rules.

    Request for Feedback

    The AESO is requesting feedback on proposed amendments to Section 503.6 and Section 503.18 by December 17, 2025. All responses will be shared in their original format on AESO Engage. In accordance with AUC Rule 017, the AESO will provide written responses to the feedback received and post these responses on AESO Engage.

    Written Consultation Materials

    Can be found in the AESO Materials section.

    Instructions 

    1. To submit your responses, you will need to be registered and signed in on the AESO Engage platform. 
    2. Please click on the "Submit Stakeholder Feedback" box below to begin the survey and provide your specific comments. 
    3. Please submit one completed survey per organization. 
    4. Responses are due on or before December 17, 2025. 
    5. All responses will be shared on AESO Engage in their original format. 

    Questions

    1. Do you agree with the proposed amendment to Subsection 6 of Section 503.6?
    2. Do you agree with the proposed amendment to Subsection 3(2) in Section 503.18?

    Submit Stakeholder Feedback
Page last updated: 26 Nov 2025, 09:09 AM