An Investigation into Wooden Pole Fire Inception Threshold in a Single Wire Earth Return System under Drought Conditions

Earthing electrodes play an important role in the reliable operation of the single wire earth return (SWER) systems. Failure in these can cause cascading effects leading to the possibility of poles catching fire. With climate change affecting the duration and extent of weather conditions such as drought, determining the performance of the SWER earthing system is important to ensure its reliability and resiliency. Since the soil is an integral part of the SWER earthing system, the electrical conductivity and thermal conductivity of a Vertosol type soil were investigated for the effects of changing temperature and moisture contents. The wooden pole was represented by different segments of resistances and was evaluated with its total resistance. A simplified electric circuit model was used to analyze the current through the pole. An analytical approach using COMSOL Multiphysics was performed in simulating the 2D axisymmetric model of a SWER system. The effect of soil cracking is reflected in a significant increase in the voltage across the wooden pole. This paper proposes an explanation of the sequence of events that lead to SWER pole fires under drought conditions.