By Corinne Reichert

December 20, 2017

The Basslink subsea cable outage of 2015-16 was caused by Basslink (BPL) exceeding its design limit, which then degraded the cable, according to reports by two global experts provided to Hydro Tasmania.

The findings on the subsea cable, which provides energy and wholesale high-speed telecommunications services to Tasmania, were made by a power cable failure expert and a thermal modelling expert from international engineering consultancy DNV GL.

“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 explained.

“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.”

Hydro Tasmania, a state government business enterprise that is responsible for a majority of the state's energy generation, said the findings “vindicate” its decision to have the outage investigated.

“We're confident this expert investigation solves the mystery of the Basslink failure for all Tasmanians,” Hydro Tasmania CEO Steve Davy said.

“BPL believed its cable could safely and reliably operate at 630MW for extended periods without overheating the copper and insulation and causing an unreasonable likelihood of failure. Unfortunately, they were wrong. The expert reports note that the cable, as designed and constructed, cannot meet the minimum operating requirements.”

Basslink responded by saying it is reviewing the reports, but has refuted that the outage was caused by anything other than a chance occurrence.

“Basslink stands by the independent investigation that was undertaken by Cable Consulting International (CCI), one of the world's leading submarine power cable experts, who described the exact cause of the subsea cable fault as 'cause unknown',” Basslink said.

“Based on the findings of CCI, Basslink maintains the cable fault was a force majeure event.”

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