A great deal of power failures occur at cable joints in Hydro-Quebec underground conduit network. Many failures are due to the degradation of the electrical connection inside these joints and the corresponding degradation of their electrical insulation. Hydro-Quebec started a few years ago an infrared thermography program for underground cable joints. This program has been implemented to perform a predictive maintenance and withdraw the defective joints before failure. This program has very strict withdrawal criteria. Those criteria have until now no real scientific and experimental basis. Moreover, there are serious discussions as to whether a punctual measurement of the temperature of a cable joint can really represent the health state of its electrical connection. Also, for how long a temperature measurement is valid and therefore what should be the best frequency of temperature measurement? A computer program based on sound cable joint withdrawal criteria has been developed. It diagnoses defective cable joints by detecting signs of electrical connection degradation before their failure.
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