Important Information on IESO’s RFP Program

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Transmission-connected Generators

Transmission-connected generators connect to our high-voltage system at more than 50 kV (50,000 volts) and are registered with the Independent Electricity System Operator (IESO).

Please refer to our Hydro One Transmission Generation Interconnection Requirements and the Protection Planning Standard at the bottom of this page for generation connection requirements for the Hydro One transmission system.

For a transmission-connected facility, generators must have our team conduct a Transmission Customer Impact Assessment, and the IESO must conduct a System Impact Assessment. The same application form is used for both studies and is submitted to Hydro One and the IESO simultaneously.

Transmission Generation Connection Process

There are six phases in the transmission generation connection process that include multiple steps and procedures within each phase that may overlap to facilitate critical in-service dates.


We recommend you first complete a pre-consultation and read these important considerations before you begin the transmission connection process for Generators.


The phases of the transmission connection process are identified below:


Phase One 

System and Customer Impact Assessments

Phase Two 


Phase Three 

Cost Recovery Agreement

Phase Four 

Design and Build

Phase Five 


Phase Six 

Approximate Timeline: An average connection can take anywhere from 18 months to over three years to complete. Certain land issues and approval processes can extend project timelines.



Customers requesting a new or modified connection to our transmission system must apply and register with us and The Independent Electricity System Operator (IESO). The IESO Connection Assessment and Approval (CAA) is a separate process that runs parallel with our Customer Connection Process. The CAA process includes a System Impact Assessment (SIA) which is conducted to assess the impact of the connection proposal on the reliability of Ontario’s transmission system.


The pre-consultation provides an opportunity for the proponent to discuss their transmission generation connection project with our planning staff. The proponent will receive more information on the transmission connection process and our staff will gain a better understanding of the project. This will help make the project successful.


The proponent should bring all relevant project information and documentation to allow for effective discussion, such as:

  • map of project location

  • GPS coordinates of project location

  • diagrams of proposed generator connection and related equipment

Contact your Account Executive or email LargeAccounts@HydroOne.com with the subject “Tx Generation Connection Inquiry” to request a pre-consultation meeting.​

  • Phase 1


    Connection Application:
    The customer prepares details of the proposed generator to be connected to the transmission system to initiate the process.

    Pre-Consultation: We will meet with the customer for a pre-consultation to discuss and review available connection facilities, general technical requirements, and responsibility to perform the identified connection work.

    Customer Submits Application Form: The customer completes the System Impact Assessment (SIA) and Customer Impact Assessment (CIA) application for a generation facility and submits to both us and the Independent Electricity System Operator (IESO).

  • Phase 2


    Note: This Phase takes approximately five months to complete for a renewable generation project.

    Customer Impact Assessments: Completion of the System Impact Assessment (SIA) and Customer Impact Assessment (CIA). The SIA study is completed by the IESO and the CIA study by Hydro One.

    Study Agreement Negotiated:
    A Study Agreement is negotiated to determine the Terms & Conditions of the CIA.

    Final draft SIA is posted by the IESO:
    The final draft SIA is posted by the IESO, triggering our team to finalize the CIA. The CIA highlights significant impacts, if any, to other affected transmission customers early in the project development process and thus allow an opportunity for these parties to bring forward any concerns that they may have.

    SIA Completed:
    We issue a final CIA report to the Electrical Safety Authority (ESA), IESO, Connection Applicant, and other Transmission-connected customers in the study area. The IESO issues and posts the final SIA report to their website.

    The customer will be invoiced for the CIA amount, if required.

  • Phase 3


    Connection Estimates:
    Phase 3 provides cost estimates for the connection based on the proponents' requirements and the outcome of the SIA/CIA. It also evaluates the financial contribution required and identifies construction responsibility for the transmission facilities required for the project. This process is initiated through a Connection Cost Estimate Agreement (CCEA) to obtain Connection Estimates.

    Preliminary Engineering (optional):
    Hydro One may conduct a high-level engineering assessment of the proposed connection to identify any major issues with the connection at an early date to speed up the connection process. A Preliminary Engineering Agreement is executed to initiate this work.

    Agree on Schedule and Scope:
    We exchange information with the customer to allow the scope, cost, and schedule for the project to be developed by our Engineering and Construction team.

    Cost estimate is delivered to customer:
    We present the project costs in accordance with the terms of the CCEA. Costs depend on scope and complexity.

  • Phase 4


    Cost Recovery Agreement:
    The Cost Recovery Agreement Phase places both the customer and our team in a position to proceed with design and construction of the transmission facilities needed through a finalized Connection and Cost Recovery Agreement (CCRA).

    Pre-CCRA Letter Agreement:
    A Pre-CCRA Letter Agreement may be executed to place orders for material or to commence design engineering at an early date.

    CCRA is negotiated and executed:
    We work with the customer to negotiate and execute the CCRA based on the agreed scope of work in Phase 3. This step initiates detailed engineering, the ordering of equipment, and acquiring the necessary approvals, permits, and licenses for the project.

    Connection facility responsibilities:
    The CCRA will define responsibilities for connection facilities for Hydro One and the customer with regard to the project. The CCRA provides the scope of work chargeable to the Proponent, scope of work not chargeable to the Proponent, Generator connection work, estimated capital contribution, payment schedule, statement of engineering and construction costs, form of easement. Date of grid connection is finalized.

  • Phase 5


    Design and Build:
    The Design and Build Phase may take up to a year or more to complete depending on the complexity of the project. The customer will undertake the contestable portion of the work and we will undertake the non-contestable portion of the work.

    Prior to commencing construction, the following items must be completed:

    • The IESO Notification of Conditional Approval for Connection;

    • Any Regulatory, Provincial, Municipal approvals;

    • Real Estate and Property Agreements or Land Acquisition Agreements in place

    • Environmental Assessments; and

    • Transfer of land rights required by us.

    Detailed engineering and project design completed:
    The connection requirements, standards, detailed engineering, project design, metering, and milestones are completed and approved by our team for our work and the Contestable portions of work.

    Equipment and project material procurement:
    We work with the customer to procure necessary equipment and project materials.

    Construction of connection facilities:
    The required customer connection facilities are built as per:

    • The IESO Market Entry Process, which must be initiated by our team or the customer as required;

    • The Connection and  Cost Recovery Agreement (CCRA) scope of work; and

    • The final approved design, taking into consideration any modifications as directed by the OEB and other provincial and municipal organizations.

  • Phase 6

  • Commissioning:
    The Commissioning phase involves inspection and testing of the connection facility to prepare for In-Service.

    The TCA negotiations are initiated:
    We negotiate the Transmission Connection Agreement (TCA) with the customer in preparation for connection.

    Finalizing the TCA:
    We work with the customer to finalize the TCA, including the Operating Schedule, transmission tariffs, high-voltage equipment data, and special connection considerations. The TCA must be executed before the customer’s facilities are allowed to be placed into service. The TCA must be completed before commissioning can begin.

    Our facilities are commissioned. We notify the IESO of equipment ready for operation.

    Customer facilities commissioned:
    Customer submits Commissioning Plan 45 days prior to the In-Service date for review and comments. Customer performs and completes commissioning activities on customer-built facilities, including the submission of the COVER to us and the IESO.

    Customer facility goes into service: Connection to our transmission grid is completed.

    Customer submits final documents: Customer submits final “As Built" Connection documents and Station Single Line diagrams within 60 days of connecting to our system.     


    CCRA is updated with actual costs: We will append the CCRA with the final invoice (credit, where applicable) to reflect actual costs within 180 days of connection and will provide to the customer with the final invoice if applicable. 


    End: Connection Process is complete.


Important Transmission Generation Connection Considerations

Consider the following ways to save time and money: 
  • Engage an experienced consultant familiar with generation connections in Ontario.

  • Ensure adequate time for acquiring and potentially transferring land rights for the connection facilities.

  • In executing a connection project, proponents should identify any potential or planned design changes to both our team and the IESO as soon as possible after the changes are considered. Failure to identify and report these changes to both parties could result in connection delays, connection refusal or additional costs.

Take advantage of the following resources for information:
  • One of our representatives is assigned to each active project

  • All project communication should be made with this representative to ensure effective communication

  • Contact our representative to initiate the connection process.

Important Transmission Generation Connection Considerations


Review the following information before beginning the connection process:

Regulatory approvals may be required throughout the process and could have a significant impact on project timelines. They can include:

  • Ontario Energy Board (OEB) approval (Leave to Construct) is required for transmission lines in excess of 2 km

  • Environmental approvals to construct facilities on environmentally sensitive lands

  • Municipal approvals and permits, including land easements and land acquisitions

  • First Nation’s consultation and approvals.

Contestable work is the work the customer performs. Non-Contestable work is work only we can perform.

The customer must select one of three options regarding construction and ownership for any Contestable portions of the project. They are:

  • Customer build and own;

  • Customer build and transfer to us ownership, or

  • We build and own.

Cost responsibility for connection and network transmission facilities is governed by the Transmission System Code (TSC). We apply the principles of the TSC to identify costs that the customer is responsible for. There may be cases where cost responsibility may require OEB resolution, which may impact connection timelines.

Our Protection Planning Standard for Transmission Generation Connections document provides generation customers with a valuable guide to the protection requirements needed to support generation connection applications on our Transmission Network. This document can be downloaded below (Adobe Acrobat Reader required).

Download The Protection Planning Standard

Hydro One considers Battery Energy Storage System (BESS) one of the fastest developing technologies that will provide wide-ranging benefits in support of electrification and growth in Ontario. Currently, there is a gap in the development of consistent standards and the existing standards do not address the potential impact of BESS fires on critical transmission infrastructure. To support the consistent and safe integration of BESS facilities in Ontario, Hydro One — with support from experts at Fire Risk Alliance — has developed the BESS Fire Protection Risk & Response Assessment Standard for the industry.

Download the Fire Protection Risk and Response Assessment Standard