18 November 2020
Looking after our existing power stations is the biggest part of Hydro Tasmania’s annual workload and budget. There are rolling schedules of maintenance and outages planned years in advance, which often take more than a year to complete. But even though we’ve been doing this for decades, there are sometimes still a few surprises in store.
Over much of 2019-20, that was the situation facing a Hydro Tasmania team at Wilmot Power Station, near Mount Roland. Things got so difficult that Wilmot was jokingly renamed “Wilnot”.
Commissioned in 1971, Wilmot is part of the Mersey Forth Power Scheme. It draws water from nearby Lake Gardiner on the Wilmot River, but sits on the north-west shore of Lake Cethana. It can discharge up to 15 cubic metres of water per second into that lake, which can then be reused for further generation downstream. Project Manager David van Emmerik explained that this configuration made planning a major overhaul of Wilmot an intimidating project.
“Whenever you’re not generating, water is spilling down the Wilmot River and you’re losing all the energy value in the water,” David explained. “Although Wilmot’s just a single 32 megawatt machine, the impact of the outage is the equivalent of having a 50 megawatt machine out of service because of the losses downstream. So we were under a reasonable amount of pressure to get things done in a timely manner.”
The outage began 30 September 2019 after more than a year of preparation, with a return to service scheduled for July 2020. You may be thinking that perhaps the pandemic was the reason for any delay, but when the pandemic hit in March the reassembly was still going reasonably well. The problems were more technical in nature.
The first of two major issues was a problem with ‘achieving machine alignment’, which means making sure the machine’s vertical shaft doesn’t deviate from its axis while spinning. Mind you, the shaft is over 10 metres long, spins at 600 revolutions per minute with a rotating mass of 80 tonnes, and the amount of ‘throw’ – how much the shaft can safely move off-centre – is about the thickness of a sheet of paper. That throw is controlled by the generator’s ‘thrust block’, which has to be heated for installation then cooled before testing in a process that takes a minimum of 48 hours to complete… and which was eventually performed 16 times.
“So there’s a month’s delay,” David sighed. “Looking at the original records from commissioning in the ‘70s, they’d had a lot of trouble with this part of the machine and they spent about six months trying to sort this out.”
The second major delay came when the generator’s upper guide bearing was ‘wiped’, which means the bearing’s surface effectively melted due to the high speeds at which these machines operate. This seemed to confirm the Curse of Wilmot, until the problem was painstakingly tracked to the set-up of a single component used for lubrication.
Wilmot site manager Josh Wilkes has over 15 years’ experience with Hydro Tasmania, including 10 as a supervisor, but this was his first project at this scale.
“There were good days and bad days,” Josh reflected.
But Dave only had praise for Josh and the entire site team.
“Of things that happened on this job, I’m doubtful that any would’ve been better handled by someone more experienced, unless they’d struck the particular issue at another station, and even then I’m sceptical,” Dave said.
As you would expect, COVID-19 presented the team with further challenges they had to overcome. Before the pandemic, there were often up to 40 people on site, with many working in closely in tight spaces. Hydro Tasmania’s number one focus is keeping its people safe, so its entire workforce across multiple sites had to make many changes. New processes were established and crew sizes were pruned to their absolute minimum.
“With a smaller team, the reality is you are normally less efficient,” Josh said. “But we were getting far more done than I ever predicted, because everyone was just having a go. We ended up working six days a week in two shifts, working 19-20 hours per day. Whatever was thrown at them, they kept going. I’m not sure I’ve been lucky enough to work with a team like that before.”
Dave said the breadth of experience within Hydro Tasmania means there is an understanding that complex work on older infrastructure will not always go according to plan.
“While things haven’t been perfect, the fact is that most of the stuff we planned went well,” Dave said. “For me, the focus was not so much on just getting the machine back in service, but about keeping people safe. It’s great to be in a business that has that focus and that’s prepared to not only learn from mistakes, but to give people a go.”
Wilmot Power Station finally returned to service in early September, nearly a full year after disassembly began. With preparation beforehand and the final clean up – and a new coat of paint – it has taken the better part of two years to complete. And this is just one of 30 power stations.
“The final days felt strange,” Josh said. “I remember talking to a few of the fellas and it didn’t feel real. We’d been that close that many times, then all of a sudden it actually happened.”
“I’ve already moved across to the Lake Echo refurbishment, so the things that caused us pain at Wilmot are the things I’m already targeting!”
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