GB266608A - Improved method and apparatus for testing electrical insulators - Google Patents

Abstract

266,608. Austin, A. O. July 31, 1926. Detecting faults.- The dielectric strength of an insulator is tested at a potential difference greater than that at which a flashover would normally occur by supplying charging-current at intermediate potentials to points spaced apart between the points of application of the test voltage. Fig. 1 shows an insulator having a metal flange 1 attached to the insulating body 2 by which it is normally attached to the cover of a transformer or oil switch, the end 5 being immersed in oil. When tested in air, therefore, flashing- over takes place at a lower pressure than under working conditions. In order to permit a higher test pressure in air to be applied between the flange 1 and the insulated conductor 3, rings 8, 9, 10 are spaced along the portion 5 and are supplied with intermediate voltages regulated by means of condensers 12 in series across the secondary winding of the testing transformer 6. The condensers 12 may be shunted by resistances 11. Alternatively the rings 12 may be connected to tappings on the secondary winding of the transformer, either directly or through condensers. Alternatively the rings may be connected through condensers to one terminal only of the transformer secondary winding. Fig. 6 shows an arrangement for testing an insulating shell 20, to which the test pressure is applied by means of electrodes 21, 22. Rings or sleeves 23 - - 27 are maintained at intermediate pressures either by their own relative points of a series of condensers 28 connected across the transformer secondary winding 29, or to tappings on the secondary winding, or to points on a potentiometer. The sleeves 23 - - 27 are spaced apart by insulators 30, and may be of wire screen to facilitate observation at all points. In a modification, Fig. 7, the control sleeves 36, 37 are separated by insulating members 28, 39 so proportioned as to set up the desired intermediate pressures in the sleeves due to their capacity. The members 38. 39 have metal coats 40 connected by leads 41 to the control sleeves and electrode. The control sleeves and insulating members may be connected by cement layers 42, or otherwise, and mav be adjustable. The control sleeves 45, 46. 47 below the insulator 44 under test are covered by insulating material 48, which may be in sections. The electrostatic field and the relative voltage gradient of the control sleeves 36, 37 may be affected by insulated control members 43. A similar arrangement may be employed for controlling the field below the test insulator.