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To assess the fire safety of cables in the service process, the influence of thermal-aging temperature on the combustion properties, pyrolysis properties, and mechanical properties of civilian-type flame-retardant electrical cables was investigated. Flammability test shows that the LOI value of the sheath increases with the rise of thermal-aging temperature, primarily ascribed to the formation of a dense carbon layer. Cone calorimeter test shows that the total heat release (THR) value and residual mass of the cables firstly decrease and then increase as the thermal-aging temperature rises. After 21 days of aging treatment at 120 °C, the THR and peak heat release rate values of the cable are reduced to the lowest values of 88.9 kW m−2 and 109.2 MJ m−2, respectively. TG analysis shows that the onset decomposition temperature of the sheath first increases and then decreases with the rise of the thermal-aging temperature, where the onset decomposition temperature declines sharply after 150 °C thermal aging for 21 days. Mechanical test shows that as thermal-aging temperature increases, the elongation at break of the sheath decreases sharply, while the tensile strength increases significantly. This is mainly because the molecular structure of the aged sheathing material is changed, as supported by SEM and FTIR analyses. [ABSTRACT FROM AUTHOR]

Thermal aging of natural ester oil shows drastic reduction in partial discharge inception voltage (PDIV) and a significant variation is observed only above a certain aging time, under AC, DC, high frequency AC voltages and with harmonic voltages with different total harmonic distortion. Weibull distribution studies on PDIV measurements indicate a reduction in scale parameter (α) with increase in thermal aging temperature. A characteristic reduction in breakdown voltage was observed with the thermally aged ester oil, under AC, DC and standard lightning impulse voltage. The breakdown voltage variation with aged ester oil follows normal distribution. Ultraviolet (UV) analysis of ester oil thermally aged at 160°C has revealed a regular shift of the derived absorbance parameter to longer wavelengths. The interfacial tension and turbidity exhibits an inverse relationship with the thermally aged ester oil. Gas chromatography/mass spectrometric analysis of the thermally aged ester oil predicted the formation of more carboxylic acids and ketones with aging duration. The steady-state fluorescence on thermally aged ester oil exhibits a shift in its emission profile, which is in tandem with the UV absorption spectroscopic analysis. Fluorescence analysis can be adopted as a real-time monitoring tool in transformers, to understand the condition of liquid insulation. The viscosity dependence on the wavelength of derivative absorption maxima follows a direct relationship with the thermally aged natural ester oil.