This paper reports the critical investigation on the streaming current of ester fluids towards power transformer. The optimization of benzotriazole (BTA) additive is tested based on the streaming current analysis considering its influence with and without the temperature. From the experimental results, the BTA concentration of 130 ppm on ester fluids observed a negative streaming current. The influence of temperature increases the streaming current of ester fluids.Only a minimal change is noticed in the viscosity of ester fluids with the addition of BTA but to the contradict, an increased dissipation factor is observed. The Response surface methodology (RSM) algorithm is being utilized as an optimization algorithm to identify the permissible level of BTA under transformer standstill and normal operating temperature conditions.