ABOUT 200,000 South Australians experienced power outages overnight after the state was separated from the Victorian network.

Energy Minister Tom Koutsantonis said the issue was upstream in the power supply system as the problem was caused in Victoria.

Around 220 megawatts was lost in SA, affecting about 200,000 South Australian customers. Some lost power for 15 minutes, others for up to an hour. But most properties had power restored by 2am.

Among those worst affected was the Olympic Dam mine, which lost power for four hours. It’s the second time in about two months the mine has been badly affected by a statewide blackout.

BHP chief executive Andrew Mackenzie issued a scathing statement saying Australia’s unreliable energy supply system was unacceptable and needed to be fixed, because it was affecting investment and jobs.

In late September, a disastrous blackout caused major chaos across the state when hundreds of thousands of people were left without power, some for days.

Far "OUT" just got the SMS now to say restored, which it did at 1:30am. lol. @theTiser pic.twitter.com/cyMbrhlXWd — Roy (@VandervegtRoy) November 30, 2016

Mr Koutsantonis said load shedding could be very disruptive and he hoped families and businesses were not too inconvenienced by the outages.

“It has been confirmed that in the early hours of this morning a fault on the Victorian side of the Heywood Interconnector caused the interconnector to trip overnight, which resulted in load shedding to areas of South Australia,” he said.

“South Australia’s grid operated effectively as an island and load began to be restored within half an hour, with SA reconnected to the national grid at around 5.11am.

“The event also emphasises just how important it is to supply our local generators with affordable gas.

“We are working with other states through the COAG process to modernise the National Electricity Market and implement reforms that will make it more stable and fairer to all states.”

In a statement, the Australian Energy Market Operator confirmed the SA power system separated from Victoria at 1.03am on Thursday.

It resulted in localised outages in the state for up to an hour, together with the disconnection of the Portland smelter in Victoria.

Adelaide Lunchtime Newsbyte December 1 Adelaide Lunchtime Newsbyte December 1

The separation of South Australia was due to an issue on the Victorian transmission network, impacting the flow via the Heywood Interconnector to South Australia, with the root cause still under investigation.

Approximately 220 megawatts was lost in SA, due to the need to balance the frequency of the network.

A Victorian smelter was also disconnected from electricity supply as a result of this fault, with power being restored to the smelter from 4am.

The Australian Energy Market Operator is working closely with Victorian transmission network service provider AusNet Services to identify the cause of the fault.

After last night’s outage, there were reports the SA Power Networks messaging system designed to alert customers to power outages was either slow or never received.

But SA Power Networks spokesman Paul Roberts said the issue would have related to the speed of restoration.

“Some outages lasted 15 minutes so it would be a case of a message going out and power being restored as the message was being sent,” he said.