South Australia blacked out by bad bespoke software, not wind farms

'Non-credible event' triggered safety settings

The Australian Energy Market Operator (AEMO) says wind-powered electricity generation's “intermittency” had nothing to do with the blackouts following South Australia's catastrophic storms in late September.

In its ongoing investigation of what caused the “system black” event on 28 September, the AEMO says the storm caused a loss of 445 MW of wind output (out of a total loss of 900 MW), rather than the 315 MW of its original estimate.

However, AEMO's updated preliminary report (PDF) makes it clear that the political assertions made about wind energy were false.

“The most well known characteristic of wind power, variation of output with wind strength (often termed ‘intermittency’), was not a material factor in the events of 28 September 2016”, the report states on page 21.

Only 20 MW of wind power disconnected due to excessive wind speed. Instead, most loss of wind output was down to how the wind farms' control systems were configured – in particular, the settings for “voltage ride-through” events, which the report notes are proprietary settings in the control software.

“Wind turbine control systems are set to provide a fault ride-through response when voltage dips to below 80% to 90% of its normal voltage as seen at their low voltage terminals,” the report explains (page 21).

“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.”

The setting in question meant nine of the 13 wind farms online at the time of the storm reduced their output or disconnected, because they detected between three and six disturbances in too short a time.

Those nine wind farms – Clements Gap, Hallett, Hallett Hill, Mt Millar, North Brown Hill, Hornsdale, Snowtown North, Snowtown South and The Bluff – were set to invoke the safe mode if there were between two and five “ride-through events” in two minutes – and the other events on the network hammered all of them (as Vulture South speculated earlier this month).

The AEMO notes that the ride-through events happened between 16:17:33 and 16:18:15 on 28 September – a mere 42 seconds.

It's also worth noting that all of the wind farms that stayed online during the storm have one thing in common: they were in the south-east of the state, close to the Murray Interconnect which only ceased operating when the whole system went dark.

Some generators have told AEMO they've already changed their voltage ride-through settings, while others are checking back with turbine manufacturers to see if they can safely reconfigure their systems.

AEMO is also less-than-thrilled about how much it didn't know regarding the ride-through settings – because vendors tried to keep the information to themselves: “AEMO will consider in the longer term the most appropriate level of disclosure and verification for settings embedded in proprietary software control systems”. ®

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