AC Volume Breakdown and Surface Flashover of a 4% NovecTM 4710/96% CO2 Gas Mixture Compared to CO2 in Highly Nonhomogeneous Fields

AC pre-discharge currents, breakdown, and flashover voltage measurements are reported in a 10 mm needle-plane arrangement in a 4% NovecTM 4710/96% CO2 gas mixture and compared with CO2 for pressures up to 8.8 bar abs. Flashover measurements were performed on different solid dielectrics (Al2O3_filled epoxy resins, PTFE (Polytetrafluoroethylene) and PE (polyethylene)) for different roughness surface finishes. The effect of fixed conducting needles at various positions on electrical strength is reported. A strong nonlinear behaviour as function of gas pressure was observed for all the studied parameters (gas, needle position, solid insulator, insulator roughness). The non-linear behaviour is attributed to the inception and quenching of glow corona, in the interval between inception and breakdown or flashover voltages. It is found that a 4% concentration of NovecTM 4710 in CO2 has a breakdown/flashover voltage ≈ 1.14 higher than CO2. The glow corona-induced stabilization effect is seen for pressures between 2 and 5 bar abs for all the studied parameters. The peak flashover voltage and its associated pressure of the different insulators are strongly dependent on surface roughness. At 8.8 bar abs, the flashover voltage level obtained with various materials was ordered as follows: PTFE > PE-UHMW > Epoxy > HDPE(High-density polyethylene).

Coconut Shell Powder and Electrical Tree Inhibition of Solid Insulator

Electrical tree phenomenon commonly occurred in solid insulator material resulting from the inconsistency of stresses during the manufacturing process. The treeing phenomenon will degrade the characteristic of insulator and may lead to breakdown. The use of filler in the manufacturing process in order to enhancing the insulation property is a popular approach. This paper presents the use of coconut shell powder (CSP) filler in epoxy resin for inhibition of electrical tree growth. The particle sizes of CSP varied from 62, 75 and 125 µm. The CSP is filled with the ratio of 0.1, 0.2, 0.4, 0.6, 0.8, 1.0, 2.0 and 3.0% by weight. We aim to observe the effects of varying the combination of CSP particle sizes and the ratio of epoxy resin for an inhibition of electrical tree growth. The electrical tree was tested by applying AC voltage of 15kV to the test sample and conducted for 360 minutes in this experiment. When the epoxy resin using CSP filler of 1% by weight is fixed for the particle size of 62, 75 and 125 µm, electrical tree length is at 1.24mm, 1.382 mm and 1.78 mm respectively. Whereas, when the particle size of CSP at 62 µm is fixed, a tree length is 1.98 mm and 1.24 mm for the ratio of 0.1 and 1% by weight respectively. Our study demonstrates that the epoxy resin using CSP filler at a ratio of 0.1% by weight can shorten length of electrical tree when compared with a ratio of 1.0% by weight. The electrical tree length was affected through the changes of permittivity by addition of CSP compound.