Some examples of failures resulting in large areas with prolonged outages include Perth (May 1994) and Sydney Jan 1991. Recent storms in Cressy, Victoria (January 2020) brought down 6 high voltage transmission towers and damaged a further 2. The fallen structures, uncontrolled electric currents, and electricity loss to customers, are all potential hazards. In Plumpton Sydney Jan 2019, high voltage lines fell onto houses (causing fire) and endangering homes, neighbourhoods and motorists on M7 Freeway.
South West Victoria – 31 January 2020
In Victoria, there was an extreme localised storm event on Friday, 31 January 2020 that caused six 500 kV double circuit overhead line towers to fall over and one severely damaged near the town of Cressy in South West Victoria. Winds in excess of 160 km/hr created a strong downdraft known as a downburst that is believed to have flattened six steel transmission towers completely.
The damage to the towers caused trips to both lines and impacted supply to the Alcoa Portland aluminium smelter, and resulted in a disconnection of the Heywood interconnector between Victoria and South Australia, separating South Australia from the National Electricity Market.
Emergency restoration structures were temporarily erected and the first line was re-energised by 17 February 2020 and the second line was back in service by the 3 March 2020.
South Australia – 28 September 2016
In South Australia, on Wednesday 28 September 2016, tornadoes with wind speeds in the range of 190–260 km/hr occurred in areas of South Australia. Two tornadoes almost simultaneously damaged a 275 kV single circuit transmission line and a 275 kV double circuit transmission line, approximately 170 km apart.
The damage to these three transmission lines caused them to trip, and a sequence of faults in quick succession resulted in clusters of generation (Wind Farms) to trip and Heywood interconnector to disconnect. As the supply-demand became imbalanced, frequency decline resulted in a state wide blackout at 4:18 pm within 2 minutes from the start of the event.
The first customers had power restored by 7:00 pm on 28 September 2016 and about 40% of the load had been restored by 8.30 pm, and 80 to 90 % had been further restored by midnight. It was a swift response from ElectraNet and AEMO to re-electrify the entire state.