Patent GB-395661-A (GB)
Title: Improvements in electric protective arrangements
IPC: H02H3/30
Filed: 1933-03-24
Abstract: 395,661. Electromagnetic relays &c. ; protective cut-out arrangements. INTERNATIONAL GENERAL ELECTRIC CO., Inc., 120, Broadway, New York, U.S.A.- (Assignees of Allgemeine Elektricitõts-Ges.; 2, Friedrich Karl-Ufer, Berlin.) March 24, 1933, No. 8974. Convention date, March 24, 1932. [Class 38 (v).] An A.C. protective relay, the operation of which is dependent upon the phase relation of two currents, is operated through the medium of an electric arc discharge tube the biased grid of which is subjected to the action of three voltages, the first proportional to one of the currents rectified in each half wave, the second proportional to one half-wave of the other current which is arranged to be normally 90‹ out of phase with relation to the, first voltage, and the third to the other current arranged so that normally alternate half-cycles oppose.the second voltage, the first two voltages acting to restrain the operation of the relay and the third during alternate half-cycles to operate the relay the anode current of the discharge tube including a releasing or tripping coil. As applied to a line section 1, Fig. 1, the currents whose phases are to be compared are obtained from current transformers 2, 3. The tripping or releasing coil 5 is connected in the plate circuit of an arc discharge tube 4, the grid circuit of which is biased by a battery 14 and contains three series-connected resistances 10, 9, 7 across which the three voltages are impressed. These voltages are derived as follows : (1) from the transformer 3 through pilot wires or a wireless link 12, 13 and a single rectifier 11 ; (2) from a no-load transformer 6 fed by the transformer 2 and a bank of double-wave rectifiers 8, and (3) from the primary circuit of transformer 2 without a rectifier. These three voltages for normal conditions are represented by the curves 22, 21 and 23 respectively in Fig. 2, and thus a resultant voltage is always produced during normal conditions above the origin line so that no current can flow in the anode circuit of the tube 4 and consequently the coil 5 is not energized. When however the phase angle of the current derived from transformer 3 shifts in relation to that derived from transformer 2 due for example to a fault in the feeder section 1 (see dotted curve 24) a resultant voltage below the origin is produced below the line momentarily during the cycle. The grid is thus made sufficiently positive to permit anode current to start and in accordance with the well-known characteristic of the arc discharge tube the releasing current is maintained until the anode potential is removed. This action occurs for all phase displacements of voltage curve 22 within the phase limits indicated by a. To increase the slope of curves 21 and 22 near their zero value without having too high amplitude resistances 9, 10 may be made of a material having a hyperbolic resistance-current characteristic such as that described in Specification 292,110, [Class 38 (iv), Electric supply and transmission systems &c.], the relay then operating satisfactorily with widely-varying current values.