Funding: Joint
NEETRAC PROJECT #: 12-061
Date Closed: 6/1/2016

Underground Transmission Systems are viewed by some utilities as "New Technologies" and by others as "Established Technologies". Independent of the new or established perspective, utilities and specification preparation bodies such as the Association of Edison Illuminating Companies (AEIC) are very interested in understanding the true meaning of industry wide performance surveys conducted to date. The most recent document is CIGRE TB 379 from WGB1.10, issued in 2009. Unfortunately, there are some issues that limit the usefulness of this document in the North American context.

This project sought to expand on the information in this document by surveying both manufacturers and utilities and focusing on cable systems installed since 2000, including components that failed in service and excluding third party damage. NEETRAC simultaneously collected data on failures and installed lengths and then identified components that failed, considering both HV (69 - 150 kV) and EHV (230 – 400 kV) cable systems. The disbursement of component failures was then obtained and the most likely failure rate and most likely failure range were estimated. Finally, a perspective on the "bathtub curve" for HV & EHV cable systems was provided. Although not requested, some (but not all) of the data were provided with specific times in service before failure or a range of times before failure. There was a sufficient amount of this data to be able to identify if there were different failure modes and different relative failure rates. The information also provided some understanding of when failures initiate. Through this project, it was found that North American HV & EHV Service Performance data for modern extruded systems differ from the CIGRE data. This could be due to differing data sets, larger North American participation, reduced confirmation bias, and/or increased data.

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