An update on the September 28 blackout published today by the Australian Energy Market Operator (AEMO) shows nine wind farms shut down due or reduced output to the “voltage ride-through” settings on their turbines, triggered by the day’s fierce storm causing multiple faults on the grid.
As previously reported, the sudden loss of voltage overloaded the main interconnector to Victoria, leading to the blackout.
InDaily has learned that at least one operator was unaware of the sensitivity of the shut-down setting, describing it as a “sleeping dog of an alarm”.
However, the new report says a key concern about wind farms – “intermittency” or fluctuations in voltage – wasn’t a factor in the day’s events.
Another criticism levelled at wind farms – that they shut down in high winds – appears to also have been of little or no consequence. The report finds only 20MW of power was lost due to wind turbines shutting down due to the fierce winds (immediately before the blackout, wind was generating 883MW in SA).
The report says the voltage ride-through settings on the wind farms operated as designed – that is, to disconnect or reduce turbine output when three to six disturbances are detected within a defined time period.
That’s exactly what happened on 28 September, with AEMO reporting that five system faults occurred within 88 seconds, leading to six voltage disturbances.
Four of the 13 SA wind farms operating before the blackout remained in service, including one which initiated its ride-through mode multiple times but was set to a limit of more than six of these events.
After the blackout, there were transient reductions in output, spread across all wind farms, including those that did not suffer from a sustained reduction in output.
Thermal (conventional) energy plants continued to operate through the faults, giving fuel to those who were quick to blame wind power for the blackout.
But proponents of renewables will take heart from the report as it shows, in effect, that the wind farms operated as intended, and their settings can be adjusted to ensure the same response doesn’t happen again.
AEMO says several operators have already taken action to revise the settings on their turbines so they can ride through a higher number of disturbances.
The report also says further investigations are underway into why several conventional back-up systems – including contingency generation for Port Lincoln – failed to operate as they should.
Energy expert Dylan McConnell, from the Melbourne Energy Institute, says the sensitivity of the ride-through settings – presumably put in place by the turbine manufacturers – had surprised at least one of the wind farm operators.
The unnamed operator told him the settings were a “sleeping dog of an alarm, undocumented in the alarm list and descriptions”.
He quoted the operator as saying: “It is extremely disappointing to find a piece of code that has not been described and that has been implemented into a system with high lightning probability.
I will initiate an immediate search through these units with their controls personnel to see if there is anything else that we don’t know about. Clearly with identical units with identical code they would all have to be considered as a single credible contingency.”
McConnell said the latest AEMO report was unlikely to settle the political debate.
“I don’t think there’s any chance of that,” he said.
However, the report was close to finalising the details of the blackout’s cause.
“It’s hard to point the finger at anyone really, apart from the storm,” he said.
Under the hypothetical scenario of zero wind energy in South Australia, and the two mothballed Port Augusta coal-fired stations still being in operation, it was difficult to say whether the ultimate result would have been different.
“How it would have occurred if Northern and Playford (power stations) were still there, it’s very unclear, because they would have still been on the other side of the fault,” McConnell said.
State Energy Minister Tom Koutsantonis jumped on the report, saying it confirmed that the intermittent nature of wind energy had nothing to do with the blackout.
“This is a software issue – not a problem with renewable energy,” he said. ” I am pleased that AEMO will now lead investigations at a national level to ensure all wind farms around the country have the appropriate settings they need to sustain the types of voltage shocks we can expect in Australia.”
He said “political opportunists” owed South Australians an apology “for using this event to pursue their anti-renewables agenda”.
The report reveals that, before the blackout, AEMO didn’t believe the transmission lines were at risk, so didn’t see the need to take pre-emptive action
“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 report says.
“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.”
AEMO found that the restoration of electricity began after three hours, with 80 to 90 per cent restored within another five hours.
It will release a further update ahead of the December COAG Energy Council meeting but its final report, including recommendations, would take up to six months to complete.
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