The state government-owned utility explained that during the replacement of old electricity lines to the refinery on July 13 "there was a problem that caused one of the steel electricity towers to fold over and bring the transmission lines down".

Caltex has declined to put a damage bill on the incident but the cost is likely to be in the tens of millions of dollars.

An 18-minute power blackout at the same refinery in 1995 resulted in Caltex receiving a $7.25 million insurance payout.

Electricity has been restored to the refinery but there is still no back-up.

The normal levels of network redundancy will be available prior to the end of September, according to Energy Australia, but the damaged transmission line would not return to normal operation until next year.