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    Available Transfer Capability Risk Mitigation Measures Overview

    The Alberta Interconnected Electric System (AIES) experienced a significant disturbance event on June 7, 2020, at 2:50 p.m. due to the tripping of the interties with British Columbia (BC) and Montana (MT). This resulted in impacting customers within Alberta through the unexpected activation of the province’s Under-Frequency Load Shed (UFLS) program.

    At this point, the AESO has completed its initial investigations into the incident and the system’s response to the event including generation, load, load shed service for imports (LSSi), and system inertia. 

    Based on the preliminary investigation, the AESO has implemented initial mitigation measures to reduce the risk of a reoccurrence of impacting customers in Alberta through unexpected activation of the province’s UFLS program when under high import conditions. These initial mitigation measures include:

    • arming additional volumes of LSSi;
    • monitoring system inertia in real time and reducing BC/MT Available Transfer Capability (ATC)  if the inertia falls below a certain threshold; and,
    • during inclement weather conditions along the Alberta-BC intertie corridor, reducing BC/MT ATC to as low as 550 MW if high imports are occurring. 

    These mitigation measures will remain in effect until the AESO has completed its investigations and has evidence of improved response, particularly from generation and LSSi within the province, to under frequency-related system events.

    Stakeholder Information Session

    The AESO hosted an information session on July 28, 2020 where an update was provided regarding reasons for the trip, system performance during the event, and the mitigations implemented in order to reduce the risk of impacting customers in Alberta from such system events in the future. 

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