Thermoconductivity effects on electrical installations using horizontal directional drilling

With limited access and right-of-way areas for the installation and/or relocation of underground utilities in urban settings, it is increasingly necessary to explore cost-effective techniques to make these installations more feasible. One method that has gained growing acceptance is the use of Horizontal Directional Drilling (HDD) to install underground utilities including telephone, sewer, water, natural gas, communication, and electrical conduits Directional drilling enables the installation of utility systems with minimal impact to surface activity and is rapidly becoming a preferred method, particularly in established urban environments, due to its competitive cost over conventional surface trenching. Electrical utilities have employed HDD for installing underground distribution conduits & cables to provide improved aesthetics in urban areas. A key concern for such installations is the dissipation of heat, and the effect on cable current carrying capacity (ampacity rating) resulting from the thermal properties and possible void formation of the bentonite-based drilling fluids typically used during directional drilling. Subsequently, the evaluation of the thermoconductivity of a bore installed by HDD is an important research area to determine the integrity of these installations. This paper discusses the results of on-site research to evaluate thermoconductivity of a multi-duct (duct bank) electrical feeder installation. Special prepositioned thermal sensors were installed to capture long-term thermal data used to evaluate the affects of such installations on the cable ampacity rating.