Powercor has agreed to plead guilty to one charge relating to the St Patrick's Day fires that ravaged south-west Victoria in 2018.

Energy Safe Victoria (ESV) initially charged Powercor with six offences after its investigation found the fires at Garvoc and Terang were caused by its infrastructure.

Up to a dozen homes, as well as farm buildings, fences and cattle were destroyed.

But yesterday in the Warrnambool Magistrates Court, ESV agreed to withdraw five of the charges, including all those related to the Garvoc fire, which its investigation attributed to a rotten power pole that snapped in high winds.

Powercor will now plead guilty to one remaining charge of failing to minimise risk of bushfire, which relates to powerlines that clashed in high winds at Terang, sparking one of the March 17 fires.

Investigations blamed infrastructure

ESV's initial investigation into the Garvoc fire alleged Powercor had failed to identify that a power pole was compromised.

"At around 9pm (on St Patrick's Day, 2018) the pole snapped and the high-voltage conductor hit the ground and ignited vegetation," an ESV statement said.

But with the dropping of the Garvoc charges by ESV yesterday, Powercor claimed its inspection and maintenance policies had been vindicated.

"We are satisfied with this outcome, as we strongly contend the necessary safety processes and procedures to maintain the network were followed, as approved by ESV at the time," a Powercor spokesperson said in a statement.

"In relation to the Terang fire, we have pled guilty to one charge of 'failing to minimise risk of bushfire'.

"The 2018 fires in the south-west region were devastating and we acknowledge the impact it has had on the community."

ESV chair Marnie Williams said in a statement that it was "the duty of every major electricity company to keep the community safe from bushfire danger caused by the failure of their assets".

"Energy Safe Victoria has held Powercor to account regarding the Terang fire and will not hesitate to hold other power companies to account for failing to manage and operate their electricity assets safely," she said.

The long-running matter will return to court on December 13.