*Pic: Secondary damage further along cable
Geelong Star …
An inconvenient truth Part 3 The balance of probability … ?
Despite what I believe is a huge amount of circumstantial evidence to the contrary, including that in Part 2 ( HERE ) concerning cable reliability or MTBF (Mean time between failures). The Tasmanian Government is proposing to sue Basslink for damages claiming the cable was over-driven by Basslink and suffered a consequential internal failure.
In a civil court the criteria is not “beyond reasonable doubt” but “the balance of probability”.
My calculation of the MTBT statistic is very likely to be quite conservative compared to that required by insurance companies to calculate their actuaries.
When you consider that the insurance entities can be faced with the possibility of such huge payouts, as in this failure of Basslink.
The higher the odds against self-failure the better, otherwise premiums would have to be set at an uneconomic figure for cable operation.
Also it is extremely likely that the insurance carries operational clauses. In other words the insurance company prescribes operational conditions under which the cable must be operated based on the manufacturer’s specifications. Basslink has a continuous rating of 500 mWatts.
Basslink Media Statement 10 March 2016 was a clarification of an earlier statement: It confirmed that the outage on 20 Dec 2015 the cable was importing power into Tasmania. The accompanying graph indicated that the imported power level was about 50% of load capacity at the time of failure. The cable had been run essentially at a constant load since midnight until approx 8am on the day of the failure tracking a target load of approx 480 mWatts. The targets are almost certainly programmed in, according to buy and sell market conditions and computer tracked. They were within the operating specification of the cable.
From my experience with much lower powered very high voltage 160 kilo Volt DC electronic driven and computer controlled monitored PSU systems is they have very comprehensive monitoring and data logging of their operating parameters.
In the event of a fault being detected, being electronically driven by an SCR switching system the power can be shut off in tens of thousandth of a second – instead of hundreths of a second – as the old electro-mechanical protection switches. This means there is vastly much less energy for the cable point of failure to blow in a spectacular manner whether the fault is internal or from external means.
My own experience with failed cables: there was no external signs of damage from internal failures.
During research for my first articles in 2016 on this saga I noticed that the Basslink cable was the first cable to use a semi-conductor impregnation fluid in the cellulose (paper) insulation. One property of this fluid – mentioned a little boastfully – that it had a negative temperature co-efficient of resistivity.
Resistivity is in simple terms the goodness factor which determines the voltage electrical insulation quality of a material. Obviously the resistivity factor has to as high as economically and practically as possible for cables such as Basslink to withstand the very high voltages involved.
All insulations in operation leak electrons minutely and it is this leakage when a cable fails (either internal or external) that increases dramatically and activates the shutdown of the driving electrical supply.
However, in the case of Basslink, because of the semi-conductor impregnation fluid the amount of operating leakage is proportional to temperature.
Unless there are other technical parameters that I am not aware of, this leakage could be detected and used to determine the average operating temperature of the cable in real time. With computer magic further data can be derived allowing for the early detection of thermal runaway conditions.
In simple terms Basslink could be the first cable to have real-time temperature monitoring.
Even without real-time temperature monitoring, the statistical reliability of internal cable failure is so high, a requirement by insurance companies.
Ockham’s razor is the name of a long-running ABC radio science show ( HERE ). The name is taken from a philosophical principle in science which states “the simplest solution to a problem is most likely to be the correct one”. Alternate solutions become more unlikely as they increase in complexity.
Applying Ockham’s principle of “simplest solution” one would have to say the cable was struck with an external mechanical force as it is by far the most plausible in common sense.
Firstly the puncture in the cable that is consistent with being struck with a powerful pointed object and rolled with the blow releasing the impacting object.
Whilst single cables being struck by a moving object tend to be hooked, Basslink is a tri cable, that is, three cables, the active feeder, the return and the fibre optic communications cable, bound together. A tri configuration has a different mechanical reaction, rather than tending to be hooked as in the case of a single cable, they tend to roll on the longitudinal axis with the applied force and release the moving striking object.
An external blow also has a potential for greater electrical trauma. By giving marginally more time before the protection system shuts off the supply.
Secondly there is the secondary damage further along cable (see photo above).
Whilst many commentators contend this could be from a grappling iron. The picture I believe was supplied by Basslink as part of the initial damage press release. I doubt if grappling damage would be photographed in mistake for damage from another cause. Further, the damage looks as if it were scraped over a wide area rather than spot grabbed.
It is this combination of damage which indicates that trawl net weights by nature of their design and operation must be very seriously considered as the cause of Basslink failure.
The two arguments – one of very high statistical reliability from internal failure and secondly the nature of the physical damage to the cable are complimentary.
Indicating a “balance of probability” that Basslink was struck by an External Mechanical Force and most probably from the weights of a fishing trawler net.
Whilst the Tasmanian government is claiming that Basslink over-drove the cable there is no indication at all in the Basslink data that in the hours before failure that it had done so.
Hydro’s modelling must rank, in technical terms, as an extremely complex attempt to find an alternative reason for the cable failure and, under the Ockham’s Razor philosophy, a least likely option.
In the article by John Hawkins on the 27-07-18 the AFMA made a rare public statement at comment # 31:
This comment supported a case that the Geelong Star took a westerly route which did not cross the Basslink cable, with graphical evidence. Against most mainstream reasoning that Geelong Star took an easterly route and crossed Basslink on the way to fishing grounds in NSW.
John Hawkins asked in reply comments #32&33 some very pertinent questions concerning the integrity of the chart that still needs to be answered.
My immediate reaction to AFMA chart, as an electronics person, was just how secure is the VMS from being duped?
Also against this AFMA statement there is the serendipitous comment in a Tasmanian Times article by Clive Stott on 21 January 2017, link below:
Comment #9 and I quote:
“I’ve got a mate who knows someone who worked on Geelong Star reckons they were in the area on the day and has a copy of part of the ships log”.
Such serendipitous information verified, would immediately alter the whole legal arena.
However, so powerful is the “balance of probability” technical case of external mechanical trauma, then it must also be asked first, if Geelong Star was not responsible, what vessel was?
In the deafening silence of meaningful governmental communication on the Basslink saga it was almost unimaginable that the AFMA, a federal government agency, came out and made this written statement in TTimes.
It has been the reluctance to reveal verifiable data on either the cable or Geelong Star by State or Federal government or their appropriate agencies that is causing the great Basslink cable “who dun it” mystery.
This is in contrast to the press releases by Basslink, the cable owners and operators. The limited but substantial information they have provided, seems to fit the commonsense physical and technical aspects of the Basslink scenario.
The current technical stance of the Tasmanian government on the Basslink saga is worrying – and to me borders on the irrational.
You might say the plot thickens.
You also may say, fairly or unfairly, that Geelong Star still does remain an “inconvenient truth”.
*Bio of Kelvin Jones: Technically trained and qualified in the UK by a major electrical engineering manufacturing company in Power Engineering with Switch and Protection specialisation, moving on to defence electronics, commissioning RADAR and development of underwater weapons. TV transmission, field work and commissioning work on industrial electronics and HVAC carrier protection. Research in cellular and fibre optics communications. Field work on scientific, bio, and medical instrumentation with extensive work on Medical Imaging particularly CT scanners and Nuclear imaging. Mature age universty studies in computer science and Technology with emphasis on the viability of renewable energy technology on legacy power grids.
• Kelvin Jones: A logical postscript …