Investigating the impedance of a wooden power pole after a pole fire

Wooden pole fires caused by leakage current flow are a major problem faced by various power distribution utilities in Australia and many other parts of the world. This paper investigates a fire at the bolt mounting a transformer to a 22kV wooden structure experienced by one of the electricity distribution utilities in Australia. A comparative analysis is undertaken between the damaged pole and an undamaged pole of similar ages and species. The effect of sapwood conductivity and varying moisture content on leakage current flowing through the wooden structure is studied. The impedances of each pole under different weather conditions are also examined in detail. A relatively low leakage current magnitude is observed to be enough current flow to create sufficient heat, causing smouldering. A combination of environmental factors and pole configuration created the right circumstances for the resulting pole fire.