A methodical experimental study was carried out to understand the partial discharges initiated due to particle movement in transformer oil under different frequencies of the AC voltage, by adopting UHF technique. The rise time of the partial discharge current pulse formed due to particle movement is 2ns. It is observed that the frequency content of the signal radiated due to partial discharges generated due o particle movement in the electrode gap lies in the UHF signal range, with its dominant frequency at near 1 GHz, irrespective of frequency of the supply voltage. The UHF signal magnitude and the time required for 100 UHF signals to form shows direct correlation. When the applied voltage is increased above levitation voltage, the UHF signal magnitude formed due to particle movement increases, irrespective of supply voltage frequency. Ternary diagram clearly indicates that irrespective of frequency of the supply voltage, the UHF signal location in the ternary diagram is the same. © 2011 The Institute of Electrical Engineers, Japan.