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Assessment of Operational Incident on July 9, 2020

October 8, 2020

Ontario benefits from use of Remedial Action Schemes that increase the reliability of the province’s transmission system. When transmission capacity is limited – due to a planned maintenance or forced outage, for example – the IESO deploys a Scheme that will select generation or load to almost instantaneously, and automatically, shut down if another transmission line trips off. This ensures that system limits are not exceeded and reliability of the power system is maintained in a cost-effective way.

On July 9, a 230 kV transmission circuit connected to the Bruce Power site was forced out-of-service for emergency repairs. To prevent potential damage to transmission and generation equipment in the area, the IESO prepared and implemented an operational plan, which included use of a Remedial Action Scheme. 

In this case, the IESO mistakenly selected an incorrect Scheme option which immediately triggered a Bruce generator to shut down, as per the design of the Remedial Action Scheme. The IESO is reporting this operational incident because it had a market impact, increasing market payments to suppliers by an estimated $17 million, and correspondingly reducing their contractual payments paid through the Global Adjustment by the same amount. While there was no increase to system costs as a whole, due to the way costs are allocated Class A customers incurred an estimated $2M in additional costs while Class B costs were reduced by $2M.

At no point was the reliability of Ontario’s electricity system at risk. The IESO is taking steps to prevent this from happening in the future, including additional staff training.


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