The Basslink subsea cable fault that led to the December 2015 outage has been described as ‘cause unknown’ by the investigating team.
Basslink, a subsea cable connecting George Town in Tasmania and Loy Yang in Victoria, experienced a fault on December 20, 2015, approximately 100 km off the Tasmanian coastline in Bass Strait.
The independent investigation was recently completed by UK’s Cable Consulting International (CCI). The investigation, which spanned more than six months, encompassed forensic examinations and laboratory analysis in Italy and the UK.
As part of the investigation, CCI also consulted with Materials Technology to undertake some specific materials testing.
CCI determined that the fault had occurred within the cable; the fault was not at a location of a joint, or a lead sheath to armour bond. There was no evidence of any pre-existing mechanical damage to the cable. The point of initiation within the fault path and the direction of propagation of the electrical failure could not be determined due to the severity of the fault damage, Basslink explained.
The operating conditions at, and preceding, the time of failure were no different to those of the year of 2015 and the cable was within its thermal rating. The insulation adjacent to the failure site was sound and showed no evidence of thermal ageing. A sample of cable remote from the fault site was in sound condition.
“We have provided the report in its entirety to Hydro Tasmania and the Tasmanian Government and trust it will provide them with sufficient expert evidence to accept that the fault was a force majeure event. Given this, we would like Hydro Tasmania to recommence meeting its contractual obligations to Basslink immediately,” said Malcolm Eccles Basslink chief executive.
“Despite best efforts, the CCI investigation has concluded that it is not possible to determine the cause of the fault. It is not uncommon that the cause of the fault remains unknown based on other past incidences of submarine cable outages,” he said.
Basslink has accepted the findings of CCI and will not be undertaking any further testing, the company added.