Partial Discharge Behavior of Technical Air, CO2, and CO2/O2 Mixtures Under Varying Pressures with Metallic Protrusion

Abstract

Due to environmental concerns, there is a growing trend toward sustainable insulation gas alternatives for $\mathbf{S F}_{6}$. Understanding the dielectric behavior of these alternative gases is essential for ensuring component and system reliability. Normalized differential (NoDi) plots were employed to study the partial discharge (PD) performance of technical air, pure $\mathbf{C O}_{2}$, and $\mathbf{C O}_{2} / \mathbf{O}_{2}$ mixtures. The inception voltage, repetition rate, and mean charge were analyzed to evaluate the partial discharge behaviour. A high-frequency current transformer (HFCT)-based measurement system is used to detect partial discharge (PD) pulses. This setup enables detailed time-domain acquisition of fast-rising PD pulses by employing an HFCT installed around the connection to the ground electrode. With this setup, the PD characteristics of high-voltage side protrusions were examined for different gases; technical air, pure $\mathbf{C O}_{2}$, and $\mathbf{C O}_{2} / \mathbf{O}_{2}$ mixtures with different pressures. The results show that all gases have comparable inception voltages. The $\mathbf{C O}_{\mathbf{2}} / \mathbf{O}_{\mathbf{2}}(\mathbf{7 0 \%} / \mathbf{3 0 \%})$ investigated in this paper exhibits the lowest discharge magnitude among all the gas mixtures studied. For this reason, it seems to be a promising mixture for an $\mathbf{S F}_{6}$-free insulation option.