Environmentally friendly gases have been widely investigated to replace sulphur hexafluoride (SF6) in compressed gas insulated equipment for the power industry. This work presents the experimental investigations on the gas stability of HFO1234ze(E) (hereinafter referred to as C3H2F4) where a unique first breakdown voltage behavior is found for AC, DC and lightning impulse (LI) voltages. A splatter of dark colored soot is observed on the plane electrode after the first breakdown that is followed by consecutive LI breakdowns chopped on the front. The breakdown characteristic stabilizes after the first voltage withstand and the 50% breakdown voltage (U50) is calculated using the subsequent stabilized data series. This first breakdown behavior of C3H2F4 is consistently observed for different tested electrode materials and configurations. The voltage difference between the first breakdown and U50 varies significantly due to the work function of the electrode material and electric field uniformity. For AC breakdowns with comparatively higher discharge energy, the data series is more consistent after the first breakdown but with significant level of soot formation indicating that this is the main influencing factor for the first breakdown effect. Soot is identified as fluorinated carbon through X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analyses.

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SF6 alternatives with significantly lower environmental impact have been extensively researched. This paper investigates two electrode configurations and test pressures to mimic the conditions as found in MV/HV equipment to systematically compare the breakdown performance of SF6, C3H2F4 and a mixture of 30% CF3I / 70% CO2 under AC and LI stresses. SF6 possesses comparatively better breakdown performance than the other alternatives investigated in this study. C3H2F4 shows "first breakdown" behavior and only the stable data series is considered for evaluation of 50% breakdown voltage, U50. The lower boiling points of C3H2F4 and CF3I limit its potential application to medium-voltage equipment with a low operating pressure. Due to pyrolysis, there is formation of soot and iodine post-breakdown in C3H2F4 and 30% CF3I / 70% CO2 respectively. This will reduce their dielectric performance and could pose health hazard to maintenance personnel.