While the operating voltages for some instrument andcontrol (I&C) cables can be greater than 4 kV to operatepumps, controls, and provide auxiliary power, theoperating voltage for most I&C cables is near 600 V.Although the electrical stress is not nearly as high in theinsulation of these cables, an ac withstand two and onehalftimes greater than the operating voltage after asimulated design basis exposure (DBE) has been used inenvironmental qualification (EQ) to determine the abilityof an insulation to meet a 40-year lifetime at an operatingvoltage. While multiple cable lengths greater than 10 feetare needed to replicate this EQ, systematic measurementof the electrical insulation strength in harvested cableinsulations can be beneficial to better understand theremaining useful life of the insulation. This understandingcan only be realized through systematic comparison tosome level of DBE, and electrical insulation strengthmeasurement can provide a baseline for comparison withother mechanical, chemical, and electricalcharacterizations that have been utilized. Acceleratedaging of two types of ethylene propylene rubber (EPR)insulations from harvested cables was carried out, and theelectrical breakdown strength and indenter modulus forboth insulations were determined. Results showed thatdegradation of electrical breakdown strength occurred inonly one type of BIW insulation and that this degradationdid track with that measured by indenter modulus. Themethodology for using Weibull statistics for electricalbreakdown strength relative to time to failure is discussed.
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