New Theory on Pole Fires

This article follows-up on a story in the Geelong Advertiser (page 4, 19/01/2000). A rash of pole fires on the morning of Sunday, 16th January to the south-west of Geelong, left up to 22,000 households without electricity for varying periods. A combination of several factors may have triggered this "epidemic" of fires on multiple power poles. The accepted explanation for sporadic, isolated pole fires occurring in electricity distribution networks is well-known and well accepted:

But it seems odd that such a sequence of events could cause NINE pole fires to occur in a small region within the space of a few hours. One possible explanation for fires occurring in small "epidemics" within a very short time frame on interconnected feeders is as follows:

A feeder or feeders with bifurcations or multiple branchings, may have one branch isolated by fault-protection equipment. All the remaining feeders will most likely experience a sudden increase in voltage, because the fault-protection has the effect of shedding load from the originating zone substation. Thus, if there were any other cross-arms ready to ignite, they will suddenly have a more intense and energetic arc-fault eating away inside them. The generation of heat will therefore also be increased, and the likelihood of another fire within a short space of time on these remaining "live" feeders is also increased.

If this scenario has any merit, the historical record should show that pole fires are more likely at "off-peak" times (i.e. times of low electricity usage - such as Sunday mornings!) when we can reasonably expect that voltages will be very high in the distribution network.

One way that distribution utilities may be able to reduce the frequency of pole fires, is to reduce the supply voltage to nominal whenever the customer power usage is low. The technology to do this is already present in all zone substations: it is called a Line Drop Compensator (LDC). Long rural feeders may benefit from the use of line drop compensators at each regulator along the feeder, but this would be expensive. However, one suspects that the present cost burden to rural customers of excessive voltage habitually around 254 volts is a much greater cost to the Australian economy, so the introduction of improved voltage control in both rural and urban settings will have microeconomic reform benefits to the national economy as a whole. We do not live in a third-world Banana Republic do we?

Footnote: Electric sparking (arcing) in HV power lines produces a tell-tale sign on low-band VHF television pictures: Australia's television system has a picture rate of fifty half-images per second, and a mains frequency of 50 Hertz. It therefore follows that bands of "snow" on your TV screen, perhaps slowly moving up or down the screen are almost certainly Power Line Interference (PLI). This is seen most clearly on Channel 2 (the national public TV broadcaster). Check with all your neighbours, video the problem if severe, go for a walk and listen for buzzing power poles in your area. Then report the problem to your utility: Your action may prevent a pole fire in areas where wooden cross-arms are still in use.

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