Degradation mechanisms of silicone rubber (SiR) by accelerated ageing for cables of nuclear power plant

Abstract

The degradation behavior of SiR for the cable insulation by accelerated thermal and radiation ageing was studied and the degradation mechanism was proposed. The degradation was observed by the change of tensile properties, the distribution of crosslinking, and the change of weight. The chemical reaction under the both ageing in oxidation conditions was crosslinking and the oxidation mechanism was found to be the same between thermal and radiation ageing. The yield of crosslinking was proportional to the ageing time and also the dose. The effect of irradiation temperature on oxidation was accelerated with an increase of temperature above around 120 0 C, which might be due to the specific radiation chemical reactions. Therefore, the degradation by simultaneous ageing at higher temperatures above 155 0 C was much higher than that for sequential ageing, such as irradiation followed by thermal ageing or thermal ageing followed irradiation. At a high temperature, the degradation by thermal ageing under vacuum (without oxidation) was more progressed than that for the ageing in air (with oxidation). The reason was assumed to be the thermal decomposition of crosslinks between SiR molecules formed by the chemical crosslinking agent. The hardness (Shore hardness) reflected well the degradation of the SiR material for any ageing conditions.

Condition Monitoring Uncertainties and Thermal - Radiation Multistress Accelerated Aging Tests for Nuclear Power Plant Cables: A Review

“…In the environment having no oxygen or vacuum, with the aging time the EaB and 100 % modulus change little for the insulation material as compared to degradation in oxygen environment but the degradation in the TS is significant [8], reported for the SiR. Initially, the cross-links are destructed, resulting in a low density of the cross-linking.…”

“…The effect of the simultaneous stress as compared to the sequential stresses are shown in Fig. 6 for SiR [8].…”

“…At present, there is not a single monitoring method that can be applied to acquire data for predicting the long term aging performance of the cable insulation material. Even though a substantial amount of research effort having been devoted to studying the aging of cable insulation material [7][8][9][10][11][12][13][14][15][16]. It has also been a challenge for the researchers to determine the key indicators of cable aging that correlate with measurable changes in the insulation material properties, as different materials have a different composition, geometry and pass through different design and fabrication procedures.…”

Electrical treeing behaviors in silicone rubber under an impulse voltage considering high temperature

“…As a result of lightning intrusion, switching surge or commutation failure of the high-voltage direct current transmission system, a repetitive impulse voltage can be generated, which may have a serious impact on the insulation system. Silicone rubber (SIR) is an advanced internal insulating material widely used in high-voltage electrical equipment insulation due to its excellent insulating, thermal, and mechanical performance [8,20,21]. As mentioned above, electrical trees are one of the main causes of insulation failure.…”

Gamma radiation effect of polymethylvinylphenylsiloxane rubbers under different temperatures

“…This accelerated approach certainly allows for easier experimental detection of radiolysis‐induced damage, but it may also lead to deviation with the actual radiation situation . Up to date, there are few work about the study on silicone rubbers subjected to high‐temperature radiation …”