Effect of O2 on AC Partial Discharge and Decomposition Behavior of C4F7N/CO2/O2 Gas Mixture

This paper focus on the influence of oxygen on the partial discharge (PD) and decomposition characteristics of C4F7N/CO2/O2 gas mixture as eco-friendly gas insulating medium. The PD characteristic parameters and phase resolved partial discharge (PRPD) patterns of C4F7N/CO2/O2 gas mixture are, respectively, extracted and constructed. The influences of oxygen content and applied voltage on the PD and decomposition characteristics of C4F7N/CO2/O2 gas mixture are investigated based on gas chromatography-mass spectrometry (GC-MS). We find that the addition of 2-4% O2 to C4F7N/CO2 gas mixture can significantly inhibit the negative half-cycle PDs and the generation of most by-products (CF4, C2F6, C3F6, CO, C2F6O3, CF3CN, C2F5CN, C2N2). With the oxygen content higher than 6%, the accumulation discharge magnitude and discharge repetition rates of C4F7N/CO2/O2 gas mixture increase sharply, accompanying the intensification of decomposition and deterioration of insulation strength. There is a positive correlation between the mean discharge magnitude and gas mixture decomposition intensity. To avoid the serious impact of PD fault on gas insulated equipment (GIE), the optimal oxygen addition in C4F7N/CO2/O2 gas mixture should not exceed 6%.