Issue Date: -
Monday, 6 August 2007
Powerline checks need new focus to mitigate wildfires
EnergySafety does not believe that Western Power breached its regulations in managing the Toodyay powerlines that caused a fire with fatal consequences earlier this year.
The wildfire was caused by the clashing of conductors of the overhead power line near Chatcup Road, Toodyay, on February 3.
"EnergySafety considers that Western Power now needs to review its present conductor clashing mitigation program carefully in light of the findings of this investigation," Director of Energy Safety Albert Koenig said today.
"The conductor clashing remediation program will need to be modified as a result of this incident," Mr Koenig said.
"I anticipate that the information expected to come forward from Western Power's investigation of the Parryville fire incident of 7 March 2007, which also arose from conductor clashing, will support this view."
That report is expected towards the end of August.
EnergySafety is Western Australia's energy industry technical and safety regulator.
Mr Koenig said the 22,000-volt overhead powerlines in the Toodyay area were now owned and operated by Western Power, having been erected by the State Electricity Commission of WA in the 1960s.
"An outer 'phase conductor' and the underslung earth conductor, sometimes referred to as an 'earth-wire', had clashed on a day of high temperatures and strong winds. The clashing took place even though the line was built to SEC of WA standards of the day which were based on the then applicable national engineering code. Also, the bay in question was fitted with longer crossarms.
"The hot metal globules resulting from the conductor clashing fell to the ground and ignited stubble which resulted in the wild fire.
"The aim of Western Power's investigation was to identify the root cause of the conductor clashing."
Mr Koenig said the Western Power investigation, which was assisted by Perth Consulting Engineers Sinclair Knight Merz, included a survey of practices of other Australian power utilities on long bays (spans) and conductor clearances.
"The survey showed eastern states utilities have over the years adopted additional clearances for long bays and also bays with underslung earth-wires, so as to mitigate the possibility of conductor clashing. Similarly, SECWA also adopted greater conductor clearances in the mid 1970s.
"The investigation identified that the use of different conductor types as was the case at Toodyay is potentially problematic due to differential swings under strong winds, as this could lead to conductor clashing at the spacing employed. The engineering code of the 1960s didn't deal with this issue."
Mr Koenig said that the Toodyay investigation had revealed the following as key factors contributing to the clashing of the conductors of that bay, or span.
"Firstly, the particular bay had the underslung earth-wire mounted 290mm higher on the two poles than provided for in the internal practices used when the power line was built in the 1960s. The reasons for this are unknown.
"Secondly, if the line had instead been built to the practices that Western Power (nee SECWA) adopted in the mid 1970s, the conductors would not have clashed because there would then have been a larger clearance between earthwire and conductors at 50deg C."
EnergySafety believes the Western Power report has added substantially to understanding the factors that contributed to the Toodyay incident, and most likely other incidents.
EnergySafety is now asking Western Power to use this information to better identify and deal with other long spans in its rural networks that present a risk of conductor clashing and wildfires. Western Power will also consider modifying its automatic restoration switching (recloser) practices for rural high voltage feeders at certain times, to reduce the risk of fires.
Media contact: Arthur Hanlon 0408 911 322