Influence of Flexibilizers on the Thermal and Combustion Properties of Soundproof Enclosures in Ultrahigh Voltage Converter Transformer Equipment

Soundproof enclosures are essential components in ultra-high voltage converter transformer equipment. However, conventional designs pose considerable fire risks, as they may impede fire suppression efforts in case of equipment failure. This study adopted a multi-technique experimental strategy to systematically evaluate the influence of flexibilizer content on the thermal and combustion properties of soundproof enclosures. The methodology combined scanning electron microscopy and thermogravimetric analysis, cone calorimetry and thermal deformation tests. Subsequently, the entropy method was applied to quantify comprehensive fire risk based on the experimental data. The results showed that incorporation of a flexibilizer reduced thermal stability, evidenced by a decrease in the initial pyrolysis temperature from 570 K to 505–545 K at a heating rate of 5 K/min. As flexibilizer content increased, the activation energy (Eα) exhibited a pattern of initial decrease, followed by an increase, and then a subsequent decrease, with most samples exhibiting Eα values below 250 kJ/mol. Simultaneously, flexibilizer addition improved critical fire safety parameters, including reduced heat release rate, total heat release, smoke production, CO2 release rate, mass loss rate, thermal deformation temperatures, and increased CO release rate. The comprehensive fire risk score decreased significantly from 0.2801 to a range of 0.1147–0.2522 after the addition of the flexibilizer. Thus, this study provides a quantitative assessment of fire safety in ultra-high voltage converter transformer equipment through risk evaluation, offering valuable insights for developing safer enclosure materials.