What happened

A severe storm system produced two tornadoes with estimated wind speeds of roughly 190–260 km/h about 170 km apart in South Australia, downing transmission towers and causing a single-circuit and a double-circuit 275 kV transmission line to trip within seconds of each other. The resulting voltage disturbances caused nine mid-north wind farms to activate an overly sensitive fault-ride-through protection feature, cutting their combined output by about 456 megawatts within seven seconds. The Australian Energy Market Operator (AEMO) found in its final report, published in March 2017, that this sudden loss of wind generation — rather than wind-power variability itself — triggered the cascading failure that overloaded the Heywood interconnector to Victoria and caused it to trip, leaving South Australia's entire grid without a stable supply source and resulting in a state-wide 'black system' event. AEMO said low system inertia, caused by a reduced number of synchronous generators online at the time, meant automatic under-frequency load-shedding could not respond quickly enough to prevent the collapse, and concluded that if the wind-farm generation loss had not occurred, South Australia would likely have remained connected to Victoria and the state-wide blackout would have been avoided. The event prompted a formal Australian Energy Regulator compliance investigation and led to new national rules on generator protection settings and minimum system-inertia requirements. No fatalities were reported in the reviewed sources; restoration timelines and exact customer-outage duration varied by area and are not quantified here to a single figure.

When cited sources give different casualty, damage or spill figures for this event, they’re reported side by side above rather than merged into one number. See how confidence levels work.