National Research Council – the government of Canada’s premier research and technology organization – developed a diagnostic test to help utilities assess the health of aging underground cable. An agency of the Government of Canada, it conducts research and development in areas that are of strategic importance and economic value for the country.
Starting in the 1970s, the government agency sought to understand the aging phenomenon of underground XLPE cables in order to develop a better way to assess their true condition – recognizing that many utility assets installed after the Second World War would soon reach end of life. After decades of research and a decade of field testing, they developed and refined an on-site diagnostic test challenges existing testing methods.
The prevalent cable test at that time was tan delta testing, however this testing had some serious drawbacks. The test requires higher than rated voltage being applied to the cable, which stresses and potentially damages the cable. In addition, test results can often be inconclusive when using tan delta measurements – providing utilities little insights for making reliable asset management decisions.
As National Research Council (NRC)’s research into XLPE cable aging and failure progressed, the focus turned to testing for insulation health condition. Water trees have been identified as one of the most prevalent failure mechanisms in distribution class cables. Water trees are small tree-shaped channels of moisture and ionic impurities that grow over time and degrade the quality of the insulation.
NRC’s objective was to develop a safe, accurate and non-destructive testing technology to identify the extent of water tree damage in XLPE cables. It began field testing the technology in 2006 with Hydro Ottawa, the distribution company serving 326,000 customers in Canada’s capital.
The result: a unique on-site diagnostic test that measures the depolarization current when the cable is de-energized. Based on this measurement, a finite health index is assessed to help prioritize what cables need to be addressed first to maintain reliability and spend capital budgets wisely.
Traceable. Quick. Non-destructive. The benefits of this new method were so clear that it sought a partner to commercialize the service.