The upshot of hybrid defects in coaxial gas insulated switchgear

Sulphur hexafluoride (SF₆) gas insulated switchgear (GIS) is widely used in electrical power supply system and therefore needs regular preventive maintenance. In this research work, a reliable and effective diagnostic technique was used to detect SF₆ byproducts caused by partial discharge (PD) occuring as a result of more that one defect, named as a hybrid defect. A 0.2-MPa pressurised coaxial chamber prototype similar to that used in GIS was used to simulate the decomposition of SF₆ when partially discharging at 48 kV. Two hybrid defects, namely a protrusion-floating particle and a void-floating, were used. The corresponding detected byproducts using Fourier transform infrared spectrometer are SO₂, HF, SOF₂, SO₂F₂, SO₂F₁₀, SiF₄, CO, and C₂F₆ for the former, and C₃F₈ and C₂F₆ for the later. It was found that the by-product combination together with the by-product concentration can be correlated to the type of hybrid defect. Results also show that the protrusion-floating particle hybrid can be potentially more harmful than the void-floating hybrid.