The Australian Energy Market Operator (AEMO) this week provided an update to its preliminary operating incident report into the ‘Black System’ event in South Australia (SA) that occurred on 28 September, 2016, during a severe weather event.
The preliminary report relied on data from Supervisory Control and Data Acquisition (SCADA) for the initial analysis. Due to further high speed monitoring data being made available to AEMO throughout the course of the investigation, this update conducts a more thorough analysis with accurate representation of the blackout event.
In the updated report, AEMO provides detailed information on:
- Generator and interconnector responses to transmission faults.
- System Restart Ancillary Services (SRAS) facing difficulties during system restart.
- Voltage stability and corresponding effects triggered by wind generation control systems in SA.
- Market suspension and resumption sequence.
- Action and next steps.
Based on forecast weather conditions on Wednesday, 28 September, severe wind speeds (reaching up to 120 km/h) were not enough grounds for AEMO to reclassify transmission lines as vulnerable. South Australian transmission assets were designed to endure these conditions.
Reportedly, there were five system faults within 88 seconds on 28 September, leading to six voltage disturbances. Consequently, investigations show a sustained loss of 445 MW of wind generation across nine farms (replacing previous data in the preliminary report of 315 MW from six wind farms).
The sudden loss increased power flows from the Heywood Interconnector reaching design thresholds. The automatic protection system activated to disconnect in order to secure against damage of the interconnector and other transmission assets in Victoria and SA.
Heywood disconnection caused a loss of 900 MW of supply and the large deficit caused a frequency collapse more quickly than could be counteracted by frequency stabilisation measures in place.
Nine of the thirteen wind farms did not ride through the six voltage disturbances and simultaneously tripped. This led AEMO to reclassify these wind farms as a credible contingency. Reportedly, their voltage control system was set to trip after 3-6 ride-through events, which was not included in their models of operation initially submitted to AEMO during the National Electricity Market (NEM) registration process.
Five of the nine wind farms were removed from the reclassification and returned to normal operation following a reconfiguration with improved voltage ride-through settings in liaison with AEMO.
AEMO restored spot market trading to normal operation on 11 October at 10.30pm. It will continue to investigate the Black System events, particularly the difficulties faced by two SRAS providers during the system restart, when they failed to perform as expected.
AEMO will continue to advise the public forum with a more comprehensive report expected for release in December, outlining recommendations for actions to mitigate the recurrence of risks for this type of event.
The update to the preliminary report can be viewed here. (Insert Hyperlink) https://www.aemo.com.au/Media-Centre/-/media/9027D5FB69294D408E4089249F38A36D.ashx
