A connection between Port Augusta Renewable Energy Park and the national electricity grid is under investigation for causing lights to flicker and dim across South Australia for hours this morning.

Energy distributor ElectraNet said the third-party connected to the grid in South Australia's north about 1:30am causing a "voltage issue".

There have been widespread reports of house and street lights flickering across the state as a result.

South Australian Energy Minister Tom Koutsantonis said the issue was not related to AEMO's gradual end to its intervention to wholesale price caps, which started from 4am and would go for 24 hours.

The minister stopped short of assigning blame but said it could be "a connection issue".

"We don't know what the actual cause is. We know the source of the problem but we don't know who was causing it," he said.

"It could have been [the] renewable energy park, it could have been ElectraNet."

ElectraNet said it worked with the Australian Energy Market Operator [AEMO] to identify the cause and the third party was disconnected from the network.

It said power supplies returned to normal about 5.30am.

Mr Koutsantonis said large operators such as GFG and BHP noticed the "voltage fluctuations".

He denies there was an inherent problem with renewable energy.

"I don't think it was anything malicious or dangerous. I just think it's probably testing, probably either a new generator that's attempting to establish its connection to the grid after commission," he told ABC Radio Adelaide this morning.

"There was testing and as demand started to increase into the day, they pulled the testing and the flickering stopped."

Premier Peter Malinauskas said ElectraNet controls the transmission lines from power stations to localised networks.

"The transmission lines issue sits with ElectraNet and apparently there's a frequency issue there with one of their feeders," he said.

"I understand there is an investigation underway from AEMO with ElectraNet."

AEMO last week suspended the market and directed generators to pump power into the network to keep lights on.