Around 24,000 customers in northern NSW around Byron Bay went without power for more than an hour on Monday night after one of the main transmission lines tripped, causing the market operator to call for load shedding to keep the network stable.
A spokesman for the Australian Energy Market Operator said Transgrid’s 330 kV Lismore to Coffs Harbour line tripped earlier in the day, and load shedding was needed to secure network from soon after 6pm.
Essential Energy had to cut off power for about 24,000 customers in the area around Byron Bay, Lismore and Ballina after AEMO instructed Transgrid to shed a total of 40 megawatts of load.
The load shedding was required because it was impossible to direct enough supply into the affected region to meet the evening peak.
The tripping of the Lismore Coffs Harbour transmission line – which actually occurred at 5am – did not immediately impact supply because of low demand during the day, and because local solar would have met some demand.
But the tripping of the line also caused the nearby Queensland to NSW high voltage interconnector, Directlink, to trip, apparently as designed.
Directlink returned to service but because it was unable to follow dispatch targets, the options to supply power to the Lismore area to meet the evening demand – as rooftop solar stopped generating – were much reduced, putting the secure operation of the power system at risk.
AEMO says that after load shedding had commenced at approximately 18:34, Transgrid’s 132 kilovolt Armidale – Koolkhan transmission line also tripped and reclosed, and at the same time Directlink tripped and remained out of service.
It says that by 19:45, electricity demand reduced, allowing the majority of power supply to be restored by 20:00, with full restoration by 22:00.
There were also reported problems with other lines, including an unplanned outage on the line from Newcastle to the country’s biggest coal generator Eraring. That incident triggered some constraints but no load shedding it appears.
This story has been updated with new information from AEMO.
