An investigation by international cable experts into the subsea cable fault leading to the December 2015 outage of the Basslink interconnector has determined the cause to be unknown.
The independent investigation was completed by Cable Consulting International (CCI), a UK based firm regarded as one of the world’s leading submarine power cable experts.
The investigation, which spanned more than six months, included forensic examinations and laboratory analysis in Italy and the UK.
As part of the investigation, CCI also consulted with Materials Technology, a leading UK materials engineering consultancy to undertake specific materials testing.
CCI determined that the fault had occurred within the cable but 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.
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.
Basslink Chief Executive, Malcolm Eccles, said, “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.
“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.
“The silver lining in this whole exercise is that CCI found the other section of the cable it sampled to be in sound condition. This gives us confidence in the long-term outlook of the asset.”
Hydro Tasmania said it will consider the technical material supplied in the report and additional material requested from Basslink to make its own assessment.
Hydro Tasmania will also facilitate continued discussions to resolve outstanding matters with Basslink.
Tasmanian Minister for Energy, Matthew Groom, said the government does not accept Basslink’s position on the cause of the fault and will continue to pursue the matter.