###### Abstract
[PERSON] and [PERSON] [8] reported that micro-fillers are significantly cheaper than nano-fillers and more suitable for large-scale production, resulting in substantial cost savings. For example, while 3-5 wt% of nano-fillers can achieve similar property improvements, 20-30 wt% of micro-fillers are required; however, the cost-effectiveness of micro-fillers still prevails [8]. Moreover, micro-fillers have long-established reliability in power equipment [8], while the long-term performance of nano-fillers is yet to be fully verified. Additionally, [PERSON] et al. [9] pointed out that nano-fillers have a tendency to agglomerate, complicating the manufacturing process, whereas micro-fillers disperse more easily, simplifying production and improving quality control. Thus, micro-fillers are preferred for power equipment insulation design. Considering such popularity in practical cases and the industry, therefore, this research selected epoxy/Al\({}_{2}\)O\({}_{3}\) micro-composites as the test specimens. Based on its improved mechanical and thermal performance compared to pure epoxy for electrical insulation applications, research on epoxy/Al\({}_{2}\)O\({}_{3}\) micro-composites has been performed [10; 11; 12; 13]. [PERSON] et al. [10] compared the effects of fluorination treatment on the surface properties of micro-alumina-filled and unfilled epoxy insulators used in SF\({}_{6}\) gas insulation systems. It was reported that fluorination treatment increased surface hydrophilicity and that the presence of Al\({}_{2}\)O\({}_{3}\) particles affected the surface structure and agglomeration state of the composite, thereby changing the surface modification characteristics. In addition, [PERSON] et al. [11] studied the effect of particle agglomeration state on the dielectric breakdown characteristics of epoxy/micro-alumina (Al\({}_{2}\)O\({}_{3}\)) composites under temperature gradients. It was demonstrated that micro-alumina particles can alter the electrical tree growth path and dielectric breakdown time under high-voltage and high-temperature gradient conditions. Moreover, [PERSON] et al. [12] analyzed the effects of nano- and micro-alumina (Al\({}_{2}\)O\({}_{3}\)) and Al(OH)\({}_{3}\) fillers on the flame retardancy properties of epoxy composites in vacuum insulators. In the referenced study [12], micro-fillers demonstrated better combustion resistance than nano-fillers for Al\({}_{2}\)O\({}_{3}\). The prior study [13] also compared the electrical performance of epoxy resins filled with micro and nano alumina particles. Ref. [13] emphasized that although nanoparticles more effectively improved the dielectric breakdown resistance, micro alumina is still a favorable choice in terms of large-scale production and cost. Thus, it can be seen that micro-sized Al\({}_{2}\)O\({}_{3}\) fillers exhibit superior properties and offer economic advantages when selected. Meanwhile, high-voltage experiments generally involve statistical processing of experimental data. This is because high-voltage test results can vary due to experimental conditions, environmental factors, and equipment sensitivity. Hence, statistical methods are used to ensure the reliability of the results. In the study by [PERSON] et al. [14], for instance, statistical methods were employed to evaluate a breakdown voltage (BDV) distribution of insulators when analyzing their flashover characteristics. The BDV data were statistically analyzed to assess various distribution models, and comparisons between experimental data were made to identify better-performing models. Other studies have also applied statistical techniques to high-voltage experimental data [15; 16; 17]. In the work of [PERSON] and [PERSON] [15], the goal was to evaluate how the breakdown strength (BDS) of nanofluids changes when various nanoparticles (Fe3O4, Al2O3, SiO2) are added to synthetic ester. In that study, the AC breakdown strength (AC-BDS) was measured using standard electrode configurations, and the collected data were analyzed using both normal and Weibull distributions.