Insulation Characteristics of HFO-1336mzz(E) and Its Mixtures as Eco-Friendly Alternatives to SF6 for Medium-Voltage Switchgears

HFO-1336mzz(E) is considered a potential eco-friendly insulating gas, with a low global warming potential and high dielectric strength. This study investigates the insulation properties of HFO-1336mzz(E) and its mixtures with CO2 or dry air to evaluate their feasibility as eco-friendly alternatives to sulfur hexafluoride (SF6) for medium-voltage switchgears. The physicochemical properties of HFO-1336mzz(E) were first introduced and its saturated vapor pressure characteristics were analyzed to determine the optimal mixing ratio to meet the minimum operating temperature requirement for applications. Then, direct current (dc) and lightning impulse (LI) breakdown tests were conducted under uniform and nonuniform electrical fields. Under uniform fields, the dielectric strength of pure HFO-1336mzz(E) is approximately 1.6–1.8 times higher than that of SF6. For HFO-1336mzz(E)/CO2 and HFO-1336mzz(E)/air mixtures, equivalent dielectric strength of SF6 can be reached when the volume fraction of HFO-1336mzz(E) is around 40%. The synergy in HFO-1336mzz(E)/air is better than that in HFO-1336mzz(E)/CO2. Based on the breakdown results under nonuniform fields, the HFO-1336mzz(E) and its mixtures are more sensitive to the field inhomogeneity than SF6. This is also verified by the partial discharge (PD) experiment, which shows that HFO-1336mzz(E) mixtures exhibit lower PD inception voltage (PDIV) and more PD activities under the same condition.