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Remaining life
Correctly identifying the remaining life of a cable system is essential in determining the optimum time to replace the cable.
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Economy
A rule of thumb frequently used by many businesses, including utilities around the world is that approximately 10% of the investment costs can be saved for each year an investment is postponed. Remaining life estimation can therefore provide a means by which substantial savings can be realized.
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Degradation processes
Determining the rate of degradation of a cable system is crucial in correctly determining its remaining life. The type of degradation that can be expected depends on the type of cable. With polymer cable, for example, the most significant degradation results from accessories and water treeing of the main insulation. With mass-impregnated medium voltage cable, the most important degradation comes from accessories as well as from lead sheath corrosion and thermal degradation of the paper insulation. Degradation processes can also be identified for high voltage oil-filled cables, pipe-type cables and gas-pressure cables. Diagnostic tools and laboratory investigations can help in determining the present rate of degradation of the cables in the system.
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Remaining life estimation
KEMA has developed tables for most types of cables that are used to estimate the remaining life. These tables not only consider the type of cable, but also incorporate information about the present, past and future loading conditions.
In the case of paper cables, for example, thermal degradation of the paper is crucial to the reliability of the cable for several reasons. Utilities tend to apply higher loads in order to avoid installation of new cables, and the higher loading accelerates the degradation of the paper insulation. The remaining life of the cables can be estimated in this type of scenario using the techniques developed by KEMA.
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