Medium Voltage Cable Predictive Diagnostics Technique

Industrial plant engineers are required to provide safe and reliable electrical cable infrastructure that will assure maximum uptime at the lowest possible cost. As electric systems age and the availability of maintenance crews decrease, reliability of the entire system is at risk. To ensure continued reliability, industrial sites are engaged in the decision process to either replace the cable, which is very costly, or repair it at discrete locations to extend its life. Engineers assigned this responsibility are able to make better power cable system reliability decisions when predictive diagnostic tools are applied. This paper is an overview covering best practices for commissioning new installations and applying predictive diagnostic programs to aging industrial shielded extruded dielectric cable systems rated 5 kV and higher. This paper will examine failure mechanisms in extruded cable and accessories. It will also cover the IEEE 400 Guide for Field Testing and Evaluation of the Insulation of shielded power cables providing clarification between non-destructive diagnostic and destructive withstand tests. A discussion will follow which describes the adverse effects of withstand testing when the objective is to assure system reliability. Case studies from actual petrochemical facilities and other industrial sites will demonstrate the ability of defect specific diagnostics to pinpoint defects and avoid future unplanned service outages. Lastly, the use of taped metal shield will be addressed, examining the aging process that may cause it to be less reliable than other shield designs and limit the ability to assess future cable system performance.