Upcoming Voltage Reduction Test
Please note that all times are in Eastern Standard Time (EST).
The IESO has advised Hydro One that a system voltage reduction test is scheduled for Thursday, July 23, 2026. This province-wide test will consist of two voltage reduction exercises, each approximately one hour in duration. The first will be a 3% voltage reduction exercise from 09:00 to 10:00. The second will be a 5% voltage reduction exercise from 13:00 to 14:00. If system conditions are unfavorable on this date, the test may be rescheduled to a later date with as much advance notice as possible. These tests are also subject to cancellation if a voltage reduction is executed in real time, yielding similar results prior to the test date. Any cancellation or rescheduling notice will be communicated by email.
Market Manual 7, Part 7.1, Section 7 (Grid Control Actions: Readiness Programs) identifies the need to regularly test emergency procedures to ensure staff familiarity and identify deficiencies in procedures.
Part 7.1, Section 7.1.1 describes the purpose of the test, which ensures that the load reduction resulting from a system wide voltage reduction (3% and 5%) provides the expected relief and identifies operational or customer problems that may need resolution. Customers are encouraged to monitor their facilities during the test periods and report any operational concerns or abnormal equipment performance experienced during the voltage reductions.
Part 7.1, Section 7.1.5 specifies the following criteria used by the IESO, Transmitters, and Distributors in granting exclusion request approvals while voltage reduction tests are in progress:
- Safety of the employees or the public,
- Damage to equipment,
- Loss of production, and
- Violation of any applicable law.
As a Voltage Reduction Test participant, Hydro One will make requests to the IESO for exclusions from the test on behalf of embedded customers prior to three (3) business days in advance of the tests, at which point the IESO will approve or reject exclusion requests based on the criteria above within two (2) business days of the scheduled tests. To meet this timeline, customers must submit their exemption requests to Hydro One prior to 23:00 on Thursday, July 16, 2026. No exceptions will be made after this deadline.
Exclusion requests should be kept to a minimum to maintain the validity of the test results. A request for exclusion must be accompanied by the reason for the exclusion and an action plan / timelines for mitigating the exclusion in the future.
Exclusion requests from previous years will not be automatically rolled over. If an exclusion is required, you must submit it through the Voltage Reduction Test – Exemption Request online form.
Please reach out to VRT.Exemptions@HydroOne.com if you have any questions or concerns.