Adoption of response surface methodology for optimization of benzotriazole additive in ester fluids as transformer insulant

This paper reports the critical investigation on the streaming current of ester fluids towards power transformer. The spinning disc methodology is adopted for measuring the streaming current at the liquid and pressboard interface. Based on the measurement of the streaming current, the optimization of the benzotriazole (BTA) additive is evaluated, considering its impact with and without temperature. According to the experimental findings, a negative streaming current is observed when BTA concentrations reaches 130 ppm in the ester fluids, and the effect of temperature is found to enhance the magnitude of streaming current. Only a minimal change is noticed in the viscosity of ester fluids with the addition of BTA but to the contradictory, an increased dissipation factor is observed. The diffusion of BTA additive in ester fluids towards reduction in streaming phenomenon can impact the other dielectric properties inside the power transformers. Thus, it is required to identify the optimal concentration of BTA in ester fluids before implementing to real-time applications. In the present research work, the response surface methodology (RSM) is being utilized as an optimization technique with central composite design (CCD) as a tool to identify the permissible level of BTA under transformer standstill and normal operating temperature conditions. During transformer standstill conditions, the optimal concentration level of BTA provided by RSM-CCD towards lower streaming current is 106.863 ppm with its permissible disc velocity of 300 rpm. A quadratic model is being followed for standstill conditions with its R² value equivalent to 0.9889. Considering this BTA concentration as a base input to RSM-CCD during transformer operating conditions, the optimal concentration of BTA is found to be 104.265 ppm with temperature limit of 65 °C resulting in magnitude of streaming current, viscosity, and dissipation factor to 1145.33 pA, 18.43 mPa.s and 0.0159, respectively.