"The DNV GL analysis indicates that the cable had been operated by BPL in a manner that allowed it to exceed its temperature design limits during a number of periods in its service life. This overheating and subsequent cooling of the cable has resulted in degradation of the cable," Hydro Tasmania said at the time.
"DNV GL concluded that the cable failure was the probable result of electrical energy discharge within the cable as a result of polarity reversal and cooling shortly before the 20 December 2015 cable failure."
Basslink retorted that the report merely put forward one idea and did not provide any "conclusive and definitive proof".
"Hydro Tasmania's experts did no actual testing on the Basslink cable or any similar HVDC [high-voltage direct current] cables. They used a theoretical model based on certain assumptions to come to a set of conclusions," Basslink CEO Malcolm Eccles said. "These assumptions make the experts' conclusions speculative and not based on actual facts."
The Basslink Interconnector was down between December 2015 and June 2016, with the fault discovered 90.5km from the Tasmanian coastline, and removed and capped three months after going down.
"The upgrade will more than double Telstra's capacity on two subsea cables across Bass Strait to 1 terabit per second each, or the equivalent of 200,000 HD videos being streamed simultaneously," Telstra COO Robyn Denholm said.