EHV wood pole fires: Their cause and potential cures

The cause of fires in vertical pole members of wooden high voltage transmission line towers not attributable to surface leakage currents or lightning stroke has been identified as a result of excessive internal Joule losses generated within the pole wood. These Joule losses are a consequence of the electrical conductivity of high moisture content wood and charging currents resulting from the capacitive coupling existing between the poles and the phase wires and high electric field intensities. Suggested cures for the problem include the use of increased numbers of metal fasteners holding the grounding wires to the Poles to more uniformly transfer the charging current from the pole to the grounding network.