Electrode systems: a protrusion on conductor (POC), a protrusion on enclosure (POE), a crack in epoxy plate and a free particle (FP) were fabricated to simulate insulation defects in a gas insulated switchgear (GIS). $SF_6$ gas was filled in the electrode systems by 3 bar and/or 5 bar, respectively. Partial discharge (PD) pulses were detected through a $50{Omega}$ non-inductive resistor. A calibration test was carried out according to IEC 60270, and the sensitivity was 0.25 pC/mV. PD pulses were distributed in the phase of $50^{circ}{sim}135^{circ}$ and over 95% of them existed in the phase of $55^{circ}{sim}120^{circ}$ for the POC. PD pulses were distributed in the phase of $230^{circ}{sim}310^{circ}$ and over 90% of them existed in phase of $220^{circ}{sim}300^{circ}$ for the POE. PD pulses occurred in the phase of $40^{circ}{sim}60^{circ}$ and $220^{circ}{sim}300^{circ}$ for the crack, and pulse counts were 25% higher in negative polarity than in positive polarity. PD pulses were distributed in every phase unlike to other three electrode systems and the peak magnitude was measured at $118^{circ}$ and $260^{circ}$ for the FP. As described above, PD pulses were observed in positive polarity for the POC, in negative one for the POE, in both one for the crack and the FP. In conclusion, it is expected that the identification rate of defect type can be improved by considering the polarity ratio of PD pulses on the PRPDA method.