Patent GB-757342-A (GB)
Title: Improvements in or relating to electrical suppressor capacitor arrangements
IPC: H01G4/35
Filed: 1953-09-11
Abstract: 757,342. Inductors. DUBILIER, W., and DUBILIER CONDENSER CO. (1925), Ltd. Sept. 10, 1954 [Sept. 11, 1953], No. 25199/53. Class 38 (2). [Also in Group XXXVI] In an inductively wound capacitor for the suppression of mains-borne interference, and comprising two main electrodes wound into a roll with intervening dielectric layers, there being a terminal connection made to each end of both electrodes with one terminal from each of the electrodes taken out at each end of the roll, a further electrode is wound in with the main electrodes and is separated therefrom by an additional dielectric layer or layers, this electrode being connected either to a further terminal or to the metal casing of the capacitor. Thus in the arrangement shown in Figs. 1 and 3, main electrodes A, B and further electrode E separated by dielectric layers C, C1, C2 are wound into a roll G with the terminal leads A3, B3 and A4, B4 protruding from opposite ends, while the lead D from the electrode E is connected to the case H. In use, the leads A3, A4 and B3, B4 are connected in series in respective conductors of a double-pole circuit carrying interference, and the electrode E is connected to earth. The capacitance between the electrodes A and B, together with their series inductance due to their being wound in a roll, suppresses the symmetrical component of the interference, while the capacitance from each to the electrode E suppresses the asymmetrical component, which electrode should, consequently, preferably have a low series .inductance. In the modification shown in Fig. 5 the electrode E projects, as shown at D1, from the end of the capacitor winding, and the projecting edge is connected, by soldering, substantially uniformly over its whole length to a metal gauze J which is itself soldered at its rim to the casing H, as described in Specification 734,420, [Group XXXVI]. As a consequence the series inductance of the winding E is reduced, the turns being all shortcircuited to each other ; however, the series inductance of the electrodes A and B is similarly reduced due to mutual inductance with the short-circuited turns of the electrode E, and a magnetic core K is provided to the capacitor to compensate for this reduction. In addition the casing H may be divided by a longitudinal slit to prevent it acting as a complete turn. The slit may be closed with a resin seal. In a further modification, Fig. 8, the electrode E is separated into a number of separate portions E1, E2, E3, each extending for approximately three-quarters of a turn and all connected at points D3 to a common terminal D4, thus preventing the formation of short-circuited turns. In place of a terminal strip as shown at D4, connection together may be effected by means of a sector-shaped metal disc or by a suitably shaped piece of gauze, Figs. 9 and 10 (not shown). Fig. 11 shows an arrangement wherein the foil E is replaced by a metallized dielectric strip having unmetallized portions N1 which are produced either by burning away the metallizing or by suitable masking during the metallizing process. When the strip is rolled up with the other capacitor electrodes and dielectric strips and with its lower edge (as shown in Fig. 11) projecting, the capacitor appears from the end as shown in Fig. 12, the areas O carrying the metallizing then being soldered to the casing H. In a further arrangement, Fig. 14, the main electrodes A, B do not overlap but are both capacitively coupled to the third electrode E. Specification 727,496, [Group XXXVI], is referred to.