This paper evidences the influence of different parameters on the electric field on DC spacers in GIS/GIL and thus their dielectric withstand under S/IMP tests. A notable difference in term of electric field can be observed in function of impulse polarity, load condition (with/without heating current) and insulating material’s properties. For example, an overstress of 0.3pu was obtained on spacer’s surface in case of superimposed impulse test with opposite impulse polarity, high load condition and high leakage current in gas. Contrary to AC system where the simple LI tests were enough, S/IMP tests with both impulse polarity, ZL and HL conditions are mandatory to verify the insulating performance of HVDC GIS/GIL spacer. This paper gives a better understanding of the electric field distribution in HVDC GIS/GIL and helps for the design and tests

Most high voltage gas circuit breakers (HVCB) in operation use SF6 as the arc interruption medium because of its high dielectric strength and good arc interruption properties. However, SF6 also displays a high global warming potential which motivates the investigation of possible alternatives to this gas.

Space charge accumulation on High Voltage Direct Current Gas Insulated Substations can produce electrical field reinforcements in the insulation that need to be taken into account in the equipment design. The TSM (Thermal Step Method) is one of the experimental techniques allowing to determine space charge distributions in insulating materials. However localized defects (i.e. microvoids, delaminations etc) cannot usually be detected by this technique. A new numerical approach to study the influence of structural defects on Thermal Step Method currents is proposed. The method is based on a Finite Element numerical simulation allowing to simultaneously solve electrical and thermal equations. The effect of three different defects were studied. It results that ring defects, with diameters smaller than 0.4 mm, produce less than 10% of change on TSM current signals. This confirms the difficulty to detect small defects by this method. It was also observed that delaminations can produce variations in signal as high as 70%, and even generate signals of opposing sign from the case without defect.

This paper deals with creeping discharges propagating over solid insulator samples in presence of a fluoronitrile mixture consisting of 10% of fluoronitrile and 90% of CO2, under positive and negative standard lightning impulse voltages, in point-plane geometry. The solid samples used are disks made of filled epoxy resin used for real GIS insulators. The experimental results are compared with those obtained with SF6 at pressure ranging 0.1 to 0.3 MPa, while the pressure of fluoronitrile mixture is chosen to match an equivalent dielectric strength of SF6. Different characteristic parameters are investigated namely the maximum length of creeping discharges versus the gas/mixture pressure and voltage polarity. In SF6, two regimes of discharges that depend on the voltage polarity are evidenced. Under positive impulse, the mixture presents similar properties as SF6. However, under negative polarity the maximum discharge length in SF6 is much longer than in the fluoronitrile mixture.