Quelle: www.aemo.com.au (19.10.16); (Bericht 05.10.16) Siehe auch Could household battery storage have prevented SA blackout?

The preliminary report explains how severe weather moved through South Australia on the afternoon of Wednesday 28 September 2016, with high winds, thunderstorms, lightning strikes, hail, and heavy rainfall. The weather resulted in multiple transmission system faults including, in the space of 12 seconds, the loss of three major 275 kV transmission lines north of Adelaide.

UPDATE REPORT – BLACK SYSTEM EVENT IN SOUTH AUSTRALIA ON 28 SEPTEMBER 2016
AN UPDATE TO THE PRELIMINARY OPERATING INCIDENT REPORT FOR THE NATIONAL ELECTRICITY MARKET.

EXECUTIVE SUMMARY

The purpose of this report is to provide an update to the Australian Energy Market Operator’s (AEMO) Preliminary Report, published on 5 October 2016, regarding the ‘Black System’ event in South Australia (SA), which occurred during severe weather at 16:18 on 28 September 2016. This update reflects further observations based on analysis completed as at 11 October 2016. Information and observations may change or be refined as new data becomes available and further analysis is undertaken. In the Preliminary Report, Supervisory Control and Data Acquisition (SCADA) data was used to undertake the analysis. Where high speed monitoring data has been made available to AEMO over the intervening period, this data has been used for the purpose of carrying out analysis in this report. This data is recorded at a finer level of granularity that enables a more detailed analysis and accurate representation of events. AEMO has highlighted information that has changed since its initial Preliminary Report.

AEMO intends to update this preliminary information as investigations continue.

In this update, AEMO provides information about:

• Generator and interconnector responses to transmission faults.
• Restoration and System Re-start Ancillary Services (SRAS).
• Voltage stability.
• Market suspension and resumption.
• Actions taken and next steps.

Pre-event

The market was operating normally prior to the event. AEMO’s assessment concluded that, based on forecast conditions for Wednesday 28 September 2016, there was insufficient justification for reclassification for the loss of multiple transmission lines or generating units.

The forecast severe weather was assessed as increasing the risk to power system failure due to lightning, however, as there are no transmission lines in SA classified as ‘vulnerable’, this did not warrant a reclassification of transmission lines.

Wind speed forecasts were up to 120 km/h, which SA transmission assets are designed to withstand.

Event

It is now known that five system faults occurred within a period of 88 seconds on 28 September 2016. These system faults lead to six voltage disturbances.

The five synchronous thermal generators operating at the time of the event remained connected and operated up until the SA system disconnected from the rest of the National Electricity Market (NEM). The operation of these generators was not materially impacted by the system faults experienced during this event.

Investigations now show that there was a total sustained reduction of 445 MW of wind generation across nine wind farms, plus further transient reductions of 39 MW in each ride-through event. The transient reduction in output was spread across all wind farms online at the time, including those that did not suffer a sustained reduction in output. This information replaces the data (315 MW lost from six wind farms) in the Preliminary Report.

The sudden loss of 445 MW of generation increased flows on the Heywood Interconnector. The Heywood Interconnector’s automatic protection mechanism operated and disconnected to avoid damage to the interconnector and other transmission network infrastructure in both SA and Victoria. The Murraylink interconnector remained connected up until the SA system disconnected, and its operation was not materially impacted by the six voltage disturbances experienced. The design and nature of this direct current link means that it does not respond to the generation shortfall nor provide frequency control or inertia into SA.

The instantaneous loss of 900 MW of supply across the Heywood Interconnector could not be met by the generators remaining online within SA. The sudden and large deficit of supply caused the system frequency to collapse more quickly than the Under-Frequency Load Shedding (UFLS) scheme was able to act, resulting in the SA region Black System.

Nine of the 13 wind farms online did not ride through the six voltage disturbances experienced during the event. In the days following, AEMO identified this issue and reclassified the simultaneous trip of these wind farms as a credible contingency.

AEMO then worked with each of the operators of these wind farms and determined that their ‘voltage ride-through’ settings were set to disconnect or reduce turbine output when between three and six ‘voltage ride-through’ events were detected within a given timeframe. Investigations to date indicate that information on the control system involved and its settings was not included in the models of wind turbine operation provided to AEMO during NEM registration processes prior to connection of the wind farms.

The wind farm operators and the turbine manufacturers are working to propose improved ‘voltage ride-through’ settings for consideration by AEMO. As they are re-configured, the wind farms are removed from the reclassification and returned to normal operation. At the time of this report, five of the wind farms that suffered sustained output reductions in the event have been removed from the reclassification.

Post-event

Following the Black System, AEMO’s focus has been on identifying the causes of the event and securing the power system for the customers of SA.

AEMO gave permission to start restoring electricity load within three hours of the Black System event, and all load that could be restored was restored within a further five hours. The remaining load (around 10–20%) could not be restored in this time due to damaged transmission towers and lines. Since the Preliminary Report was published on 5 October, ElectraNet has constructed temporary towers, restoring three out of the four damaged lines. This has enabled all power requirements in SA, including large industrial demand, to be met from late on 12 October 2016.

System Restart Ancillary Services (SRAS) are provided by generators contracted to restart without power from the grid and provide power to the transmission network and other generating units following a Black System. The two contracted SRAS generators in SA experienced difficulties. AEMO will continue to investigate why SRAS suppliers did not perform as AEMO expected. Some new details are included in the body of this report.

Voltage stability

A rapid decline in voltage across the SA network was observed immediately prior to the opening of the Heywood Interconnector. This rapid voltage decline was consistent across the SA transmission network from the South East to the North. Once separated from the rest of the NEM, network voltage within SA momentarily returned to normal levels before the rapid frequency fall led to the Black System.

This observed reduction in network voltages is consistent with a loss of synchronism between the SA power system and the remainder of the NEM. AEMO will be conducting further analysis to confirm that these changes in network voltages are fully understood and were as expected given the circumstances.

Market suspension

AEMO returned the South Australian spot market to normal operation at 22:30 on 11 October 2016, following formal notification that the Ministerial direction to suspend the market had been revoked.

Kommentar

Wenn das Unerwartete doch eintritt. Ein Teil des Problems war offensichtlich auch die steigende Komplexität im System durch dezentrale Erzeugungsanlagen. Überraschend ist aber, dass nur einige hundert Megawatt Abweichung bereits für den Kollaps ausgereicht haben, wobei hierzu genauere Technische Details fehlen. Und wie so oft, hat auch Murphy zugeschlagen, wenngleich der Ausfall insgesamt sehr glimpflich verlaufen zu sein scheint, obwohl ein Gebiet fast dreimal so groß wie Deutschland betroffen war, wo jedoch nur knapp 1,7 Millionen Menschen leben. Berichtet wurde etwa, dass große Bergwerke die Förderung und Verarbeitung von Gold, Kupfer und Uran aufgrund des Stromausfalls einstellen mussten.