GB516710A - Improvements in or relating to methods of testing the insulation of electrical machinery and apparatus - Google Patents

Abstract

516,710. Detecting g faults. SIEMENS-SCHUCKERTWERKE AKT.-GES. July 5, 1938, No. 19943. Convention date, July 5. 1937. [Class 37] The insulation of electrical machinery and apparatus is tested by stressing it with an impulse voltage derived from an impulse voltage generator, and simultaneously subjecting it to surges produced by applying A.C. through a capacitative load and spark gaps, so that should the insulation break down under the impulse voltage which exists for a very short duration and occur at relatively long time intervals the fault is burnt out and rendered visible by the rapidly succeeding voltage impulses produced by the A.C. A transformer 1 under test is excited by a source 3 the secondary phase windings 4 being connected to condensers 6 through spark gaps 5 adjusted so that, in known manner, the spark gaps are broken down by the transformer voltage thus charging the condensers 6 which in turn discharge through the spark gaps 5 to the windings 4 which are therefore subject to current surges of short duration. The impulse generator 7 is of the Marx type supplied through a transformer 8 and rectifier 9 and connected to the test circuit through a switching spark gap 17. The discharge resistance 14 earthed at 15 is preferably connected to the Marx generator 7 through an auxiliary spark gap 13. The condensers 6 are protected by spark gaps 16. The Specification as open to inspection under Sect. 91 also states that when the impulse voltage has to be connected at a given instant of the A.C. cycle of source 3, the spark gaps 5 or 17 are provided with control electrodes, e.g., triode spark gaps may be used the third electrode, in this case, being connected to the impulse generator. The surge wave test may be effected immediately after the impulse voltage test instead of simultaneously therewith. This subject-matter does not appear in the Specification as accepted.