Abstract
This paper investigates the changes in electrical and physico-chemical properties of low-voltage power cables for nuclear application when subjected to the combined effects of gamma radiation and temperature. Electrical response is evaluated by means of the dielectric spectroscopy, while the physico-chemical changes are analyzed at different structural scales through five complementary techniques (OIT measurements, FTIR spectroscopy, swelling measurements, DSC analysis and micro-indentation). The dielectric spectroscopy and the first two chemical techniques are shown to be appropriate for evaluating the development of radio-thermal ageing in low-voltage cables. Hence, the results reported in this article suggest the effectiveness of dielectric spectroscopy as a non-destructive technique for on-site cable diagnosis.
Highlights
Low-voltage (LV) cables are widely used in nuclear power plants (NPPs) for power transmission, control of equipment and instrumentation, communication (I&C) of signals and data
Electrical insulation is often made of polyethylene or ethylene-based copolymer formulated with different kinds of additives, above all antioxidants and flame
DIELECTRIC SPECTROSCOPY Figure 2 shows the variation of the real (ε’) and imaginary parts (ε’’) of the permittivity as a function of frequency for the different ageing periods analysed here
Summary
Low-voltage (LV) cables are widely used in nuclear power plants (NPPs) for power transmission, control of equipment and instrumentation, communication (I&C) of signals and data. It has been estimated that there are about 1500 km of cables inside each NPP [1] and, since most of the NPPs built during the ‘80s and ‘90s are reaching their endof-life point, electric utility companies are trying to extend the NPPs operating life up to other 40 years. To reach this goal, assessing the health of LV I&C cables has become a key problem due to the fact that this is usually achieved through destructive techniques, e.g. mechanical tests [1, 2]. The most sensitive part in terms of ageing is the electrical insulation which surrounds the conductor and whose extensive degradation can lead to the failure of the cable.
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