GB1481978A - Electrical capacitors - Google Patents

Abstract

1481978 Capacitors ROBERT BOSCH GmbH 21 Aug 1974 [22 Aug 1973] 36678/74 Heading H1M Casing 13 of self-healing capacitor 10 has corrugations 18, 20 to permit relative movement between two parts of the easing on increase of pressure within the casing which movement is harnessed to rupture wire 25 and disconnect the capacitor, corrugations 18, 20 being of different depths and/or rigidity. When gas is generated as a result of electrical overload, after an initial lag indicated by zone I in the expansion/pressure diagram shown in Fig. 3, there is a comparatively rapid expansion (zone II) as the less rigid or deeper corrugation extends and it is in this region that the wire is arranged to rupture (point A) for early cut-out. Particularly in the case of dielectrics comprising synthetic plastics, rapid gas generation may continue after cut-out, and this is controlled and contained by the less rapid expansion (zone III) as the more rigid corrugation extends. The initial play of non-rupturing lead 27 may be such that it becomes tight during the expansion and co-operates to retard the expansion in zone III. As shown a pasteboard plate 15 is located between the capacitor roll and upper insulating cap 17. In an alternative embodiment (Fig. 7, not shown) a metal plate is used which may provide a cutting edge bearing on the rupturable wire. A deep corrugation may be provided between two shallow corrugations, the latter holding in position the capacitor roll and the casing cover as the central corrugation extends. The empty space may be filled with incombustible material such as sand occupying up to 50% of the space (Fig. 8, not shown).