Patent GB-318162-A (GB)
Title: Improvements in or relating to alternating current actuated arrangements for indicating or measuring purposes in an electric circuit
IPC: G01R19/22
Filed: 1928-05-24
Abstract: 318,162. Jackson, L. Mellersh-, (Siemens & Halske Akt.-Ges.). May 24, 1928. Commutator switching arrangements.-Alternating current measurements are made on a direct-current instrument in series with a rectifier having an interrupter contact on a membrane which is clamped at least at two opposite edges and is set into forced oscillation by means of alternating current derived from the same source as the measuring current. As shown in Fig. 1, a casing 1 contains a permanent magnet 2 having a central pole piece 3, carrying a winding 4 and surrounded by a concentric annular polepiece 3<1>. A disc of thin metal foil 5 has fixed to its centre an iron armature 6 carrying a contact 10. The membrane 5 is fixed to a ring 7 either with initial strong radial tension or with subsequent tensioning by a ring fixed to the casing 1 and pressed more or less into the membrane by screwing down the ring 7. The membrane 5 forms one of the closing covers of a flat closed box 8, the other cover 8<1> of which is of insulating material and carries a central contact screw 9 connected through a direct-current measuring instrument 20 to a source of alternating current 14. The box 8, which may be evacuated or filled with hydrogen or neutral gases for the prevention of sparking, is fixed in the casing 1 by means of a screwed ring 11. The winding 4 is connected to the source of alternating current 14 through high non- inductive resistances 12, 13 so as to bring the phase of the current in the winding 4 into phase with the alternating pressure. The measuring circuit is then broken at the contacts 9, 10 at the moment when the voltage curve passes through zero. Alternatively a small phase-regulating transformer may be employed and may be fixed to the casing 1. For adjustment purposes, the phase regulator may be adjusted until zero deflection is obtained on the instrument 20, and then displaced by 90 electrical degrees. Alternatively a phase displacement of 90‹ of the current in the interrupter circuit may be effected by means of a condenser, which is removed after adjustment. For using both valves of the wave, four interrupters may be built together, using the Graetz connection. The contacts 9. 10 may be in series or in parallel with the direct-current instrument 20. The coil 4 may be brought to a potential approximately equal to that of the measurement circuit by the arrangement of connections shown in Fig. 2 for measuring the corona losses of a conductor 21. This is connected through a measuring circuit consisting of two rectifiers 22, 23, a resistance 24, and galvanometer 25, to one terminal 26 of the high-tension winding 27 of a transformer 28, the other terminal 29 of which is earthed. The energizing coils 30, 31 of the two rectifiers are connected to the secondary winding 32 of an isolating transformer 33 and also to the terminal 26 of the secondary winding 27 of the measuring transformer, so that they are not subjected to a greater potential difference than the voltage of one energizing coil. When a phase transformer of sufficiently high insulation resistance is used, a separate isolating transformer is unnecessary.