The optimum quantity of titania nanoparticles as a filler and the surfactant ought to be added with a mixture of 20% ester oil and 80% transformer oil, which is estimated based on Corona Inception Voltage (CIV) and breakdown studies under AC and DC voltages. The addition of titania nanoparticles along with cetyltrimethylammonium bromide (CTAB) as a surfactant to mixed oil is compared with nanofluid prepared with oleic acid as a surfactant. The breakdown voltage is high under lightning impulse voltage followed by DC and AC voltages. Ultra High Frequency (UHF) signal radiated during corona activity has shown discharge magnitude less with CTAB added nanofluid. The phase-resolved partial discharge studies have indicated less spread in phase discharges with nanofluid formed with CTAB. Particle Size Distribution (PSD) studies, Zeta potential, and dielectric parameter measurements have corroborated the superiority of CTAB used as a surfactant for optimized mixed oil, which is also supported by flow electrification studies. UV and fluorescence spectra of the samples were analyzed to substantiate the influence of nanoparticles on the chemical signature of oil. It is observed that optimally dispersed nanofluid exhibits better thermal conductivity, turbidity, and flashpoint. The presence of nanoparticles exerted marginal effects on viscosity of the fluid, but no variation is observed after electrical breakdown in nanofluids, ensuring its stability. © 2019 IOP Publishing Ltd.