Experimental studies were carried out to understand the partial discharges initiated due to particle movement in GIS operated at different pressure, under high frequency AC voltages adopting UHF technique. The rise time of partial discharge current pulse formed due to particle movement is 2ns. It is observed that the frequency contents of the signal radiated due to partial discharges generated due to particle movement in the electrode gap filled with SF 6 lies in the UHF signal range, with its dominant frequency at near 1 GHz, irrespective of frequency of the supply voltage and the operating pressure. The UHF signal magnitude and the time required for 100 UHF signal to form shows direct correlation. Ternary diagram clearly indicates that irrespective of frequency of the supply voltage, the UHF signal location (signal generated due to PD) in the ternary diagram is the same. © 2011 IEEE.