In its preliminary report on the state-wide blackout in South Australia (referred to as a Black System), the Australian Energy Market Operator (AEMO) has determined the cause to be solely extreme weather and not the energy generation mix. While the storm triggered the blackout, the AEMO is now conducting an investigation into how each part of the electricity system responded.
The AEMO’s report Black system event in South Australia found that before the storm hit on 28 September the electricity system in South Australia was stable and exhibited no unusual activity.
At the time, the state’s power supply was made up of approximately 880MW of SA wind generation, 330 MW of SA gas generation, and 610 MW of electricity imports via two interconnections with Victoria. These systems were collectively supplying 1,895MW of electricity to 850,000 customer connections across the state.
However in the afternoon, a catastrophic storm hit suddenly and three major 275 kv transmission lines north of Adelaide and 22 transmission towers were damaged and went offline.
AEMO’s report found that the energy generation mix was initially able to ride through the faults, but following an extensive number of faults in a short period, 315MW of wind generation disconnected, affecting an entire region north of Adelaide.
The uncontrolled reduction in wind generation resulted in increased flow on the main Victorian Heywood interconnector to make up for the deficit. This resulted in the interconnector overloading.
To avoid damage to the interconnector, the automatic-protection mechanism activated, tripping the interconnector. This resulted in a Black System with the remaining customer load and electricity generation in SA being lost.
This automatic-protection operated in less than half a second.
Getting back on the grid
A ‘Black System start’ is a pre-defined and practised plan which was activated following assessment of the electricity system and public and employee safety.
Within approximately 90 minutes, SA transmission network owner ElectraNet started the process of progressively restoring power by progressively energise the main Victorian interconnector through to Adelaide to start Torrens Island Power Station and provide a basis to allow customer supply to be restored.
AEMO reports that by midnight on 28 September, 80 to 90 per cent of electricity that could be restored had been.
The remaining electricity load could not be restored, due to the loss of the three transmission lines north of Adelaide, together with the unknown status of a fourth line (which required physical inspection).
This effectively cut the SA transmission grid in two, isolating the north of the state.
AEMO reported the transmission lines north of the Adelaide metropolitan area could not be re-energised before visual inspection on the morning of 29 September, in accordance with standard industry practices to protect public safety and the safety of ElectraNet’s field crews.
The northern line confirmed intact was re-energised on 29 September 2016, allowing some electricity to be restored in the northern region.
Supply to the three large industrial sites in the north of the state remains constrained due to the limitations which remain in the northern region.
On 30 September, the last remaining segment of transmission supply, the southern Eyre Peninsula, was restored.
South Australian Premier, Jay Weatherill, said, “South Australia hasn’t seen a storm like last week’s in living memory.
“Based on early advice from AEMO and the experts, I have consistently said this was a weather event, not a renewable energy event. AEMO’s preliminary report supports this view.
“Friday’s meeting of Energy Ministers in Melbourne is an important opportunity to look at Wednesday’s events and begin working to ensure this doesn’t happen again.
“South Australia will be taking a leadership role to promote reform of the National Energy Market and drive further interconnection between states.”