From the AEMO report this morning:
The predicted weather front moved through SA on the afternoon of Wednesday 28 September 2016, including high winds, thunderstorms, lightning strikes, hail, and heavy rainfall.
The weather resulted in multiple transmission system faults. In the short time between 16:16 and 16:18, system faults included the loss of three major 275 kV transmission lines north of Adelaide.
Generation initially rode through the faults, but at 16:18, following an extensive number of faults in a short period, 315 MW of wind generation disconnected (one group at 16:18:09, a second group at 16:18:15), also affecting the region north of Adelaide.
The uncontrolled reduction in generation resulted in increased flow on the main Victorian interconnector (Heywood) to make up the deficit.
This resulted in the Heywood Interconnector overloading. To avoid damage to the interconnector, the automatic-protection mechanism activated, tripping the interconnector. In this event, this resulted in the remaining customer load and electricity generation in SA being lost (referred to as a Black System).
This automatic-protection operated in less than half a second at 16:18.
The event resulted in the SA regional electricity market being suspended.
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.
At 17:23, AEMO directed the SA transmission network owner ElectraNet to 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.Restoration of electricity supply started in Adelaide at 19:00. By midnight on Wednesday 28 September 2016, 80–90% of electricity (that could be restored) was restored.
The remaining electricity load could not be restored, as the loss of three of the four 275 kV transmission lines north of Adelaide, together with the unknown status of the fourth line (which required physical inspection), effectively cut the SA transmission grid in two, isolating the north of the state.
In accordance with standard industry practices to protect public safety and the safety of ElectraNet’s field crews, the transmission lines north of the Adelaide metropolitan area could not be re-energised before visual inspection on the morning of Thursday 29 September 2016. Continued poor weather conditions and high winds kept helicopters grounded, making slower ground patrols of the transmission network necessary.
The northern line confirmed intact was re-energised at 12:15 on Thursday 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.
At 21:00 on Friday 30 September 2016, the last remaining segment of transmission supply, the southern Eyre Peninsula, was restored.
Temporary transmission tower structures owned by ElectraNet have been deployed, and also contributed by network owners in other states to assist in the restoration. Access continues to be hindered by poor weather conditions and flooding. Consequently, the restoration of the second and third lines is expected to take 7–10 days.
On Thursday 29 September 2016, pursuant to clause 3.14.3 (2) of the National Electricity Rules (Rules), AEMO was directed to suspend the market in the SA National Electricity Market region by Ministerial direction by the South Australian Government under the Essential Service Act 1981.
The SA wholesale electricity market remains suspended and prices continue to be determined in accordance with schedules and processes defined in the Rules.