## 1 Introduction  
Recently, with the rapid progress of the information society, the dependence of social functions on electricity is increasing. Because of the surge in power demand, the power system is also becoming large-capacity and ultra-high voltage, and accordingly, stabilization and reliability of power facilities has become very important. Therefore, substation facilities are changing, in particular conventional air- or oil-insulated substations are changing to gas-insulated substations [1, 2, 3].  
A gas-insulated switchgear (GIS) was introduced in the 1960s in substations, and it offers high power transmission and switching capability in very limited installation space with delivery of high power and reliability [4]. The GIS tank is filled with sulfur hexafluoride (SF\({}_{6}\)) gas, which has excellent insulation and extinguishing ability as an insulating medium, and the filling part of the GIS is supported by a solid insulating epoxy spacer [5, 6]. Because of its good characteristics, epoxy resin is used for the spacer, and by using an automatic pressure gelation (APG) molding process, complex structures, such as home appliances, automobile parts, and electronic equipment parts [7, 8, 9, 10, 11, 12, 13] can be manufactured.  
Recently, due to concerns about environmental pollution and gradually depleting petrochemical resources, interest in bio-based epoxy resin to replace petroleum-based epoxy resin has been growing [14, 15, 16]. The bio-based epoxy resin is cost-effective and can reduce the stress, lower the viscosity, and strengthen the solidity of epoxy resins [17; 18; 19; 20; 21; 22; 23]. Normally, in the APG process, the resin mixture in a relatively low temperature state is supplied using pressure in a high temperature sealed mold, and the curing accelerator contained in the resin mixture reacts rapidly due to the temperature difference. Then, the mixture is changed to a gel form within a short time until the curing is completed, and this method can compensate for reaction contraction by continuously supplying the liquid mixture under pressure [24]. However, because the APG process relies on empirical predictions, the use of new materials can lead to unexpected results, so it is difficult to find an optimized process condition. Especially, in the case of bulky injection moldings, it is necessary to optimize according to each heater temperature of the mold in consideration of mechanical characteristics and stability of the product due to the temperature difference of the lower mold near the injection hole when injecting resin. However, empirical prediction is not appropriate in such complex conditions; therefore, to effectively optimize the temperature and APG process conditions of each part of the mold, accurate simulation and analysis should be performed to consider all variables, such as epoxy resin, heat temperature, etc. [25].  
In this research, the process of the bio-epoxy-based GIS spacer was simulated and analyzed to find the optimized process conditions before manufacturing. The spacer was 3D-modeled first by Moldflow, and then, the APG process was simulated using thermosetting resin bio-based epoxy composite. Based on the measured data, the simulation was conducted considering temperature, mold temperature, heater temperature, injection time, and injection pressure. The optimized process conditions were presented to suggest optimized APG process conditions, and the GIS spacer was manufactured based on the optimal conditions.