Titania (TiO2) nanoparticles dispersed transformer oil has high Corona Inception Voltage (CIV). The volume of nanoparticles and the amount of surfactant have a strong influence on corona inception voltage. It is observed that the CIV is almost the same under high frequency AC voltage. CIV reduces with increase in level of distortion of the harmonic AC voltages. Corona generates UHF signal with its dominant frequency at 1 GHz. The characteristics is the same irrespective of harmonic voltages with different THDs. PRPD analysis was carried out to understand the discharge occurrence phase under harmonic voltages and could clearly indicates that discharges always occurs at the point where dv/dt is high. In addition, it is observed that discharges in negative half cycle are high at the point of corona inception, irrespective of harmonic voltages with different level of distortions.