Aging Modeling of Low-Voltage Cables Subjected to Radio-Chemical Aging

Abstract

This article presents the development and application of a modelling approach based on quantities obtained from mechanical and electrical tests to assess the aging of low voltage cable insulation for nuclear applications. In order to obtain experimental data needed for the establishing of the models, accelerated aging is performed on coaxial cables. The first part of this paper focuses on the development of a predictive modelling for mechanical properties; this allows the evaluation of the Dose to Equivalent Damage (DED) as a function of the aging stress (dose rate). However, the use of mechanical tests for cable aging assessment presents some problems, being such tests destructive for the insulation and potentially affected by local defects. The novelty of this work lays on the introduction of a new model, allowing the definition of the end-of-life point in terms of electrical non-destructive tests. The second part of this article presents the development of aging modelling of cable insulation and correlation with experimental data obtained at different stresses, which allow the estimation of the expected life of the cable under test to be derived from diagnostic measurements of electrical properties like, e.g, tan. Finally, the application of the proposed life model to two typical real-condition nuclear environments is presented and discussed.INDEX TERMS Modelling of insulations, LV cables, Nuclear cables, radio-chemical aging, predictive modeling, cable life modeling, polymer aging, extruded cables.

Aging Mechanisms and Non-Destructive Aging Indicators of XLPE/CSPE Unshielded LV Nuclear Power Cables Subjected to Simultaneous Radiation-Mechanical Aging

“…Furthermore, regulators and plant operators are considering extending the operating license to 80 years [1]. For the safe and reliable operation of an NPP, it is essential to demonstrate that all the plant safety-related elements can fulfill their intended functions under both the normal operation and postulated events such as loss of coolant accident (LOCA) [4,5]. As a result, age-related degradation of NPP components has received more attention from regulators.…”

“…Cables transmit control signals and data, communicate between different NPP systems, and power various apparatuses [7]. The predominant cable types used in the NPPs are LV power cables and I&C cables since a typical NPP may compose about 1500 km of LV cables [5,8]. NPP LV cables are exposed to harsh conditions during their operation, and they are exposed to different stresses, as illustrated in Figure 1 [9,10].…”

“…However, the EaB measurement is a commonly used method to determine the degradation of polymers [24,25]. However, the EaB test is naturally destructive, and it requires samples removal; thus, it is not practical for on-site testing [2,5,10,26]. Therefore, non-destructive electrical-based condition monitoring techniques have been the focus of scientific interest, such as dielectric spectroscopy, return voltage measurement, and the polarization-depolarization current method [8][9][10]14,15,19,20,[26][27][28][29][30].…”

“…Therefore, non-destructive electrical-based condition monitoring techniques have been the focus of scientific interest, such as dielectric spectroscopy, return voltage measurement, and the polarization-depolarization current method [8][9][10]14,15,19,20,[26][27][28][29][30]. These techniques have been successfully adapted to various insulation systems [2,5,26,30].…”

Aging assessment of insulating materials through broadband dielectric measurements: the appropriate frequency choice

“…On the other side, broadband dielectric spectroscopy allows the definition of e.g., complex permittivity throughout a wide range of frequencies e.g., between 10 -2 -10 6 Hz. At present, very few works consider the impact of the frequency on the proposed aging marker [2]- [5]. Hence, the choice of the frequency which best correlates the aging evolution has still to be properly defined.…”