Pics: The damage ... and the culprit? Geelong Star, before its renaming. And below, Basslink cable damage, including the gouge ...
The Basslink Saga: A technical perspective …
On August 8 2016 Pete Godfrey used a letter from a national monthly electronics magazine as a basis for comment on Tasmanian Times on the Basslink saga. Mr Godfrey said …
I read a very interesting letter a couple of days ago, from a retired technician. His letter was about the Basslink cable. With the help of a few retired technician friends they have come to the conclusion that the Basslink cable was hit at speed by a large heavy object. So it seems that something being dragged by a vessel caused the damage to the cable. Was it the Supertrawler, or a Scallop Dredge. Hopefully someone will have details of what vessels were operating in the area of the damage when the cable went down. Then they will have to decide who is to blame. Was the cable laid on the surface of the seabed rather than being buried? Were the regulations around shipping and trawling near the cable too lax? Whichever way it goes, we will end up paying. Some lunatic will soon decide that we need more cables just in case it happens again.
I was the writer of that letter, with the technical input of a friend. Pete’s comments were very relevant. However Basslink was used in my original letter as an example in a wider context as a response to an editorial and complimentary article in a previous issue.
This wider context encompassed the technical, green and economic conflicts facing our legacy power systems on a worldwide basis - including the use of nuclear energy particularly the case for thorium reactors - to solve Tasmania’s energy woes.
However it did raise questions on the Basslink saga and the following is an expansion from our findings on this woeful event.
When the Gordon below Franklin dam proposal was stopped by the Green vote the long history of growth of very low-cost hydro electricity in Tasmania came to an end.
To fill a growing energy insecurity gap a choice had to be made between a thermal power plant (whatever the source of heat) and connecting to the mainland power grid via HVDC (High Voltage Direct Current) cable technology.
It should be noted now that Basslink is a high quality installation that is technically well run.
Hydro is by far the best technology available for peak load supply. Cable technology presented a glittering monetary prize to the political/economists, the ability to export highly profitable peak load power in exchange for imports of cheap off-peak power thus maintaining dam energy levels.
The downside? Such a long HVDC cable can never be as secure as a base load thermal power station no matter what the excuses made by the heads of the utilities.
It is the unpredictability of unacceptably long repair times and the possibility of being irreparable (Moyle cable Ireland to Scotland is currently being replaced) that makes a single cable unsuitable for base energy security.
The reverse is true of a new thermal power station but that would have significantly increased the cost of electricity production and seriously upset the current balance of Tasmanian energy economics. This is based on two-thirds of production consumed by three heavy industries at little more than production-cost-price with commerce and households supporting the main operations and infrastructure … plus profit at approximately mainland prices.
In 2015 the EEU (European Economic Union) published a very comprehensive survey of all marine HVDC cables currently operating in the world as part of a proposal to lay a HVDC connector between Europe and mainland America.
Of interest is the section on cable failures. These occur frequently in northern European waters, 60% are related to mechanical trauma … mainly heavy trawlers in depths similar to the Basslink failure. And in shallower waters anchors, and 10% to environment, for example Earth tremors; the rest to internal failure which are sometimes slow consequences of external trauma or manufacturing defect.
The report also goes on to state cable failures often cause considerable stress to communities, especially where repairs cannot be speedily effected. In these cable-crowded waters it is not unknown for a cable to be cut every 3 weeks. This is for all types of submerged cables … trawlers and anchors do not discriminate.
When a fishing licence was granted for a super trawler to operate in our home waters the statistical vulnerability of Basslink increased dramatically. For the first time there was a vessel type which actually worked at the deeper parts of Bass Strait. Further at these depths the cable is protected by only its own single spiral wound armour … and by burial which is sometimes insufficient because of seabed formation.
Did Basslink fail from an internal fault or did it suffer external trauma?
The confidence of the Hydro that the repair has made the cable as good as new is a positive indication that external trauma was the cause.
This long cable is made with jointed lengths. The repaired section is jointed in by the same techniques as the original laying. They remove a large section cable (several kilometres) either side of the rupture as water ingresses the layers of paper insulation under pressure of the water depth.
If it had been an internal fault, firstly, it could not be reasonably guaranteed other similar defects were not also present in manufacture elsewhere in the cable.
Secondly it is highly unlikely that an internal fault would externally appear anything more than a swelling of the damaged point.
The photograph of the damaged section issued by the Hydro shows a rupture though the armour and external sheath. The size of the bulge which is caused by destabilised internal electrical pressures was limited by very rapid action of the onshore protection systems.
The same protection would have been afforded to an internal fault of this type, breaching of the outer metal sheath would simply not occur in the very short time (probably less than 15 milliseconds) before the cable was tripped by the protection system.
The photo also shows a wire of the armour binding sheared. Breakage by expansion from an internal fault would have been by stretching … giving a shredded appearance as each wire consists of several strands.
Therefore it appears to me that a substantial force impinged on one strand of the armour, shearing it and pushing one open end through the metal sheath and into the insulation.
This would create a very high electrical stress point, breaking down the insulation and creating the burnt cavity look of the photograph. Whether such damage could have been inflicted in the original cable laying causing delayed electrical failure I think very unlikely because of the point severity and the substantial service time that has elapsed.
Research into heavy trawler Danish-Seine-type net fishing that included input from friends in the UK where the apparent ruthless activities of these vessels is better known.
The design of the the massive nets used relies on weights at the bottom and buoys at the top to balance the tow dynamics for correct operation. Whilst a net does not normally trawl the sea floor, a net out of buoyancy-balance can do just that and the considerable weights on the bottom can plough up a soft seabed significantly.
It is normal that if the design of the net is modified then tests are needed to ensure buoyancy balance for the correct operation of a trawl net.
It is known the Geelong Star left Geelong on the 16 Dec 2015 after net modifications to minimise well-publicised by-catch issues. This was the start of the pelagic fishing season and it soon turned off its compulsory AIS (Auto Identification System) which had apparently been allowed by Marine Authorities.
Pelagic fish are found in the water depths and locations similar to where the Basslink fault was found. The Geelong Star’s next known position was fishing in NSW waters two days after the Basslink failure on the 19 Dec.
In view of a need to test net performance and a possibility of a return to port for corrections it would seem prudent to me to set a course south and slightly westerly and turn south-easterly well out into Bass Strait, testing the nets en-route. This would allow for a quick circle back to port for further modifications if initial tests proved unsatisfactory.
However, if performance was proving satisfactory then an easterly course to NSW waters would be taken, whilst further tuning the nets.
Such a course leaves open the possibility of crossing the cable at the point of failure.
Apart from the AIS, ships send an auto-GPS location signal via satellite on a periodic basis similar to aircraft. however the data does not seem to be publicly available.
From my experience with HVDC cable computerised protection systems they are unable to determine the location of the fault, not even one end or the other of the cable. They usually are able to tell a lot about the conditions of the cable prior to the fault.
If the protection system was able to record the location of the fault then why did it take so long to find the fault?
Blind fault location on long cables uses pulse reflective time techniques; this is only effective over a given length of the cable.
This then requires the cable to be lifted and cut and the process repeated over the next length until the fault is located. It is a heavy laborious task. It would appear this technique was used and the cable first cut at about 80km from shore.
The second test presumably located the fault about 40km further out. It is interesting though they started at the south end, the end nearest where the fault was found (?????). Without another technical explanation how was the choice of starting at the north or south made … by the toss of a coin? Or perhaps a satellite data from a passing ships present at that location and time?
Whilst a second cable would improve reliability statistics, it would be just that, an expensive back-up. The single Basslink covers the vital baseload security and energy exchange adequately with financial contractual obligations to the private owner.
There is simply insufficient income-earning surplus hydro energy for export on a second cable and we have already experienced the catastrophic depletion of dam reserves by excessive exports over the existing cable.
Basslink is a 500 million Watt cable and that is a very significant portion of the Tasmanian grid capacity. This could be be the reasoning why the Federal Government, in my opinion, rightly, are dubious about the viability of a second cable as it seems they were in planning of the current cable.
Tasmania”s historic very low-cost Hydro electrical energy has created an unhealthy imbalance in the government’s cost structure … and industry took the brunt of the energy shortfall.
It was noticed that the State Liberal Government was extremely reluctant to introduce energy saving measures for household and consumers, paranoid may be a better word, as the Treasury coffers would have had a serious loss of revenue if consumers and commercials cut consumption.
The dam level/carbon tax issue period was also researched. It was noted during this period not only was there high export of peak power there was little import (dam level savings) of off-peak power, thus maximising profits. Also the graphs on the drain of dam levels showed a remarkably linear downward trend which would indicate a systemic intention rather than a more random curve dictated by the marketplace and operational prudence.
Also of interest during the Carbon Tax period there was reported a serious dispute between a relatively newly-appointed Head of Treasury and Finance and political masters. Evidently the new head was previously the head of Aurora and resigned, citing personal issues, leaving before his five-year term finished.
From the published data it does appear to me that the initial crisis cause is not Basslink failure but imprudent running down (for cash) of dam levels, creating the natural senario that is the primary reason Basslink was meant to protect against. The dangers of running down dam levels would have been painfully obvious to anyone technically well briefed. This scenario leads to the question … was the current government warned in no uncertain terms by the Treasury of over-exploitation of the dams?
While the obvious solution to Tasmania’s energy/economic imbalance is to shut down the three heavy industries (that is if they do not shut themselves down as seems a real possibility), the other alternative is to build a thermal power station to restore baseload security.
Either way it would mean that more Hydro energy would be available for our own peak-load needs - and safe export over Basslink at least for a while.
One further aspect in hydro technology advancement the public does not seem aware of is the dramatic improvement in water turbine technology efficiency. The famous gigantic Hoover dam in the USA upgraded its old water turbines with an eight-times improvement in efficiency over the old turbines. This means it it takes one eighth of the amount of the water to produce a unit of electricity, effectively increasing water storage by eight times for the same level of generation capacity.
It was also reported they intend in the not to distant future to upgrade again with an expected improvement from eight to 12 times. I cannot see Hydro engineers not having investigated the feasibility of upgrading Tasmanian dams.
These are big and capital intensive modifications and only Hydro engineers are able to determine thee effectiveness of such upgrades. However this technology does throw a promising dimension into the mix for solving Tasmania’s energy dilemma.
As major new infrastructure has a long lead time, unless heavy industry does cease operation, Tasmanian electrical energy security is in question for the some time to come. A price for originally choosing a glittering economic prize offered by an inappropriate technology.
There are no free lunches in energy physics.
*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.
• Pete Godfrey in Comments: … The photos of the fault released and the paucity of details did not look like a manufacturing fault to me. Thanks again, I believe that secrecy will prevail as it usually does in Tasmanian government matters, but we need to know who is paying and how much …
• Luigi in Comments: It would be simple enough for the Geelong Star to voluntarily make its whereabouts known to prove its alibi on the day of the Basslink outage. I would also be simple enough for our government to demand to know the whereabouts of the Geelong Star. Or is the six month outage just a $100 million giggle to our government? Or do they already know?
• Kelvin Jones in Comments: … Hydro engineers, if allowed to disclose the current state of water turbine technology, could answer this question very quickly. There is also a very pertinent comment that indicates the State Government is more interested in cash income than capital expenditure which is at the root of the Basslink saga which must have great weight. … At the moment I am as certain as I possibly can be that external mechanical trauma caused the demise of Basslink. There also is circumstantial evidence that there is activity of a vessel with the capability of inflicting such trauma at that time … There has been - for the last 70 years among the populous - a growing illusion, that if there is a problem, science and technology will find a solution. Economists have fallen for this trap in a big way. Most of this illusion is formed from the perceptions based on an ever-widening array of gadgets and goodies that have been incrementally introduced into our lives. They are all based on one fundamental technology ... usable energy …
• William Smith in Comments: … The only short term option would involve the reduction of the heavy industrial load with possibility of closure of one of the big three with the very regrettable loss of jobs.
• Kelvin Jones in Comments: … Brian Green’s office also commented on the large amount of censorship in a documentation that was tabled to State Parliament. Could it be that the document did contain details of the Basslink failure and the possible involvement of the Geelong Star. Disclosure on the floor of the Tasmanian State Parliament would have negated the legal protection from marine law then applying to Basslink. This could have then had a legal chain reaction back to a Commonwealth Desk? We can ask a lot more questions if that is the case …
• KAS in Comments: … The real issue with the bass link cable, is not that it was damaged – which is not that unusual for cables laid in shallow water like it is, but rather that it took so long to repair. I have never heard of a repair taking that long, and I think the reason for the delay was that they had insufficient spare cable to carry out the repair … This theory was confirmed to me by a friend who works for one of Hydro’s major customers. He told me that Hydro had told his company that the real cause of the long delay in repair was due to insufficient spare cable being available …
• John Hawkins in Comments: Kelvin thankyou for your efforts. The ABC has been emasculated by the Liberals so total silence on this important matter. The Mercury is in bed with the Liberals and will never do them a disservice ... result - total silence. The Examiner has nobody who can research or write an original story hence can only regurgitate a press release …