07 October 2016
by Ben Potter
Mystery Over SA Wind Failure
A big drop in output from six South Australian wind farms was a key event in the sequence leading to the state's blackout last week but the Australian Energy Market Operator assigns no reasons for the reduction in generation.
That left protagonists in the debate about whether wind power was the culprit - such as South Australian Premier Jay Weatherill - clutching at straws. A detailed report is a month away.
But a leading energy expert and the chief executive of company that owns Snowtown 2 wind farm - which had the biggest drop in output - said this didn't change their understanding that "the critical cause" of the blackout was transmission failure.
"The storm event took down the transmission. Subsequently a chunk of wind generation came off," Vince Hawksworth, chief executive of New Zealand-based Trustpower, told The Australian Financial Review.
AEMO's preliminary report says that in the lead-up to the blackout there was a sharp reduction in wind generation at six wind farms, the cause of which requires "additional analysis ... before any conclusions can be drawn".
Just before the collapse of South Australia's electricity system in severe storms, wind farms were supplying about 880 megawatts of capacity, Victoria's brown coal power stations about 600MW (mainly across the Heywood interconnector) and gas turbines about 330MW.
A second after two of the state's four main 275 kilovolt north-south transmission lines had been cut,123MW of wind generation dropped out at four wind farms owned by AGL Energy - the Bluff, North Brown Hill, Hallett and Hallett Hill plants.
AEMO attributed the transmission failures to "phase-to-ground" faults - lightning strikes earthing the line, bringing the voltage to zero and triggering an attempt to re-open the line.
Four seconds later, the third 275 kilovolt north-south line cut out. Two seconds after that, another 192MW of capacity was lost from the 270MW Snowtown 2 wind farm north of Adelaide and the 270MW Hornsdale wind farm, owned by France's Neoen and UK infrastructure fund John Laing.
The loss of just over 330MW of capacity triggered a massive surge on the Heywood interconnector to almost 900MW - 1 1/2 times its rated capacity of about 600MW. Heywood automatically shut down, triggering the statewide blackout.
The sequence seems to implicate the wind farms in some way and was seized upon by wind power foes.
But Mr Mountain said the amount of wind power lost in the first instance - 123MW - wouldn't have been enough to trip the Heywood interconnector. He said the fact that each loss of wind power followed seconds after a loss of main transmission lines failures strongly implicates transmission failure.
AGL declined to comment on the reasons for its wind farms dropping out.
AGL chief executive Andy Vesey said on Tuesday that renewable energy generated close to the point of consumption could make electricity networks more secure by reducing their dependence on long distance transmission networks, which are vulnerable to extreme weather.
But a report by ElectraNet, South Australia's transmission company, in August said the loss of coal generation in the state had made the electricity network vulnerable to possible voltage collapses in the case of transmission failures because wind farms can't fulfil the voltage control function that thermal power stations provide.