| 摘要 |
1,068,255. Capacitors; electric transformers; electric conductors. E. I. DU PONT DE NEMOURS & CO. Oct. 9, 1963 [Oct. 15, 1962], No. 39842/63. Headings H1A, H1M and H1T. In an electrical device, e.g. a transformer, insulated cable, or capacitor comprising alternate layers of dielectric and conductive material, the voltage at which corona first arises is increased by subjecting the device to a voltage stress exceeding the initial corona starting voltage, in an atmosphere of electronegative gas. A roll capacitor having dielectric film of e.g. polyethylene terephthalate, polycarbonate, polyolefine, fluorinated polymer, or paper has foil or metallized electrodes of aluminium, zinc, or copper and is filled with an electronegative gas, e.g. a perhalohydrocarbon; specifically octafluorocyclobutane, chloropentafluoroethane, hexafluoroethane; or sulphur hexafluoride or hexachloride; in a gas-tight container under pressure not exceeding 10 p.s.i., e.g. 3 to 5 p.s.i. Voltage from a mains frequency transformer is connected across the device, and the inception of corona is detected by a cathoderay oscillograph. Voltage is increased to exceed corona inception voltage and is maintained until corona ceases, after which it is again increased in steps until the required corona inception voltage is attained. Alternatively the voltage may be reduced to zero between each step increase, or a single voltage stress may be applied to exceed the initial corona inception voltage and held until corona ceases. The gas may be retained within the device after processing, or may be allowed to escape. Detailed examples are given. |
