Patent GB-703952-A (GB)
Title: Improvements in or relating to contact convertors
IPC: H02M1/26
Filed: 1952-01-04
Abstract: 703,952. Mechanical make-and-break switches. SIEMENS-SCHUCKERTWERKE AKT.-GES. Jan. 4, 1952 [Jan. 24, 1951; Aug. 9, 1951; Aug. 15, 1951], No. 374/52. Class 38(5) [Also in Group XXXV] A polyphase contact converter with reciprocating contacts moved by eccentrics in which switching chokes are used, has in each phase an opening and a closing contact which may be connected in series or in parallel, the opening and closing instants of the opening contact being variable relative to those of the closing contact, so that the time of overlap during which commutation takes place may be altered. In each of Figs. 2-5, which show the times during which the contacts are closed, the uppermost lines relate to the closing contacts, and the lowest two lines show the limiting durations of closure of the adjustable opening contacts. Figs. 2-5 are derived from arrangements in which the angle of displacement between the eccentrics driving the two contacts is fixed (as shown in degrees) and the duration of closure of the opening contacts is varied. Figs. 2, 4 relate to contacts in series and Figs. 3, 5 to contacts in parallel, having possible phase overlap 0‹-60‹ for three choke coil arrangements and 0‹-120‹ for six choke coil arrangements respectively. Further diagrams, Figs. 6-9 (not shown) illustrate suitable displacement of eccentric angles to achieve similar results where the contact times remain unchanged. To avoid flashover at starting the overlap may be adjustable to a negative value. The adjustment may be manual or automatic: Fig. 10 shows a construction in which pairs of contacts such as 1, 2 which may be connected in series or in parallel, are operated by push rods 3, 4 bearing on eccentrics 5, 6 mounted on shaft 7 driven by motor 8. To adjust the duration of closure of the opening contacts, cam 12 is rotated to move eccentrics 5, 6 axially. Movement of cylindrical eccentric 5 has no effect on closing contacts 1, but movement of non- cylindrical cam 6, alters its effective profile where the push rod 4 bears upon it and therefore alters the motion of the opening contacts 2. Fig. 12 shows a mechanism in which the cams 15, 16, are axially unmoved but axial movement of rod 7 displaces cam 16 angularly relative to cam 15 as a result of the different pin and slot connections 17, 19 and 18, 20. To control the converter output, the stator of motor 8 or the phase of its supply voltage or of that applied to the contacts may be shifted angularly. Alternatively the motor may have cross excitation variable through variable resistances. The two sets of cams 5, 6 may be on different shafts 7 driven by separate motors, Fig. 14 (not shown), or one shaft may be driven through differential gear from a motor driving the other shaft, Fig. 17 (not shown). Constructional elements, comprising a shaft 40 bearing cams 41 and push rods 43 operating contacts 42 mounted in a framework 44, may have flanges arranged for bolting to co-operating flanges on similar elements, so that arrangements with separately driven shafts in parallel or axially coupled shafts with a common drive may be built up. Rectifiers may be connected in parallel with the opening contacts.