Transmission towers aren’t supposed to fold like matchsticks. But in recent years, that’s exactly what has happened across parts of Australia.
The frequency and force of downburst-driven transmission failures are rising. And our current standards and systems need an urgent upgrade.
“These structures [high-voltage transmission towers] are failing in ways we haven’t seen before,” said Dr John Holmes, an experienced wind engineer and Director of JDH Consulting, Victoria. “It’s not just in Australia. But here, it’s accelerating.”
Like an invisible sledgehammer
The cause is a specific class of non-synoptic wind events known as convective downbursts or microbursts. Unlike the steady boundary-layer winds most transmission towers are designed for, downbursts are short, violent plumes of cold air that plunge to the ground, then fan out horizontally. They can unleash massive force in just a few minutes, with very little warning.
“They’re caused by a very rapid vertical motion of [cold] air at [about] 15 km,” explained Holmes. “When it starts falling under gravity this can produce strong winds – enough to damage structures.”
These winds don’t behave like the synoptic winds that transmission towers were originally designed to withstand.
“Most Australian towers were built before [the year] 2000 – and were designed for synoptic wind events,” said Holmes.
“That matters because synoptic winds allow for span reduction factors: the ability to reduce design loads because wind gusts aren’t usually aligned across an entire span.”
“But with downbursts,” Holmes continued, “there’s very little reduction. The whole structure gets hit simultaneously. In effect, they produce almost a single gust enveloping a couple of kilometres.”
In Texas in 2008, a rare dataset from a downburst event confirmed this: “There were remarkably small reductions in load,” he said. “And that’s one key reason for failures.”
Major events
The first-ever failure of a 500 kV interconnector in Victoria in 2020 marked a point of escalation.
“That was a tested product, a heavy asset, and the Australian Energy Market Operator (AEMO) never expected such an incident,” said Asif Bhangor, Director at ENGIAN Consulting Australia. “It was an eye-opener. [The tower] was literally sheared off at the foundation. The wind pressure was maybe two to three times what the structure was designed for.”
Three such failures occurred between 2020 and 2024 in the same Victorian region. This area had always been non-cyclonic in the Australian Wind Code AS1170.2.
“But what we’re experiencing is cyclonic: microbursts, synoptic downbursts. They’re now becoming more and more frequent, so clearly there needs to be some work done on risk, how to manage that risk and how to effectively mitigate the risk. There is currently very limited information in the current Australian Standards for risk management under extreme weather events.”
In South Australia in October 2024, 29 transmission structures including 19 towers collapsed in a single event, crippling multiple lines and knocking out power to more than 36,000 people. This affected industry too with the BHP Olympic Dam mine, for example, being without power for more than two weeks.
“If you think of the network like the body’s arteries, these failures are like losing a major blood vessel,” said Bhangor. “The grid can’t function without them.”
Engineering blind spots
Both Holmes and Bhangor argue that existing design standards are insufficient.
“AS/NZS 7000 – the overhead line design standard – does include downbursts in Appendix B,” Holmes said. “But it doesn’t yet reflect the impact of line length or orientation, which are critical to actual risk.”
Orientation really matters: Holmes pointed to recurrence interval data showing that north-south aligned lines are far more likely to experience damaging winds. For instance, a north-south line might see 45 m/s gusts every 10 years, while an east-west line might only face such conditions once in a century.
But these downbursts, although now becoming more common, are not new to Holmes.
“I’ve been working on this [convective downdrafts] since the 1990s, when we first started hearing about them, and we actually produced some reports for most of the mainland states, between 1997 and 1999.”
“But many of the reports and data on these risks were buried in filing cabinets for decades – until something failed and they were dug up again.”
Quantifying the threat
Following the failure of the Victorian interconnector, Bhangor saw a knowledge gap.
“There was no adequate literature on resilience and power line exposure to extreme weather. So we had to build our own risk model.”
Bhangor and his team, working through CIGRÉ (the International Council on Large Electric Systems), developed a simple Excel-based model to help assess transmission line vulnerability.
The model combines four factors:
- Network importance – How critical is the line to the grid?
- Restoration complexity – How hard is it to repair or replace?
- Historical performance – How has the line behaved under past stress?
- Route vulnerability – What local hazards (like wind or flooding) apply?
“By overlaying this data with GIS mapping and known weather risks, the tool estimates both existing and residual risk, helping engineers make better-informed decisions.” said Bhangor
“It’s not AI, it’s logic – from engineers who live and breathe this stuff.”
What can be done?
Weather patterns are sometimes wildly unpredictable so there is no single answer but both Holmes and Bhangor point to a few key actions engineers can take to build a more resilient transmission system.
- Update design standards to reflect the need for network resilience to include impact of downbursts especially considering the existing and new transmission infrastructure that is going to be built in the next 10 years”.
- Train the next generation: “There’s almost zero university coursework on overhead lines,” said Bhangor. “That has to change.”
- Model resilience alongside reliability: “It’s not just about uptime,” Bhangor emphasised. “It’s about how fast you can recover when a tower fails.”
Thousands more towers to come
Currently in Australia we have more than 3000 km of high-voltage lines under construction and up to 10,000 km needed by 2050 to hit net zero, so this problem is only going to grow.
“These failures aren’t anomalies anymore,” Holmes said. “They’re signals. And if we don’t listen, the network will keep failing – one storm at a time.”
Dr John Holmes and Asif Bhangor presented at RISK2025 the national conference for the Risk Engineering Society of Engineers Australia.