GB453248A - Improvements in or relating to electrical circuits employing cathode ray tubes - Google Patents

Abstract

453,248. Protective cut-out systems. COMPAGNIE POUR LA FABRICATION DES COMPTEURS ET MATERIEL D'USINES A GAZ, 12, Place des Etats-Unis, Montrouge, Seine, France. Oct. 14, 1935, Nos. 28357, 28358, and 28359. Convention dates, Oct. 12, 1934, May 21, 1935, and July 8, 1935. [Class 38 (v)] [See also Group XL] A circuit comprises a cathode - ray tube arranged in an electrical network with the generating voltage of the tube derived from the network and the deflection of the beam controlled by the electrical conditions in the network, whereby the beam is adapted to operate a protective, measuring or telemeasurement device or relay. The voltage of line 1 is rectified at 14 and smoothed at 15, 16 and impressed on the tube 2 so as to give rise to a beam 3, which is subjected to a field between deflector plates 5 proportional to the line current as derived from a current transformer 7, 4 being a concentrating coil. The beam strikes a fluorescent screen 9 and at a certain deflection of the cathode spot 8 from the centre 10, light from the screen passes through an aperture in a shutter 17 on to a photoelectric cell 11 controlling a H.F. transmitter 12. The transmission is received at a remote receiver 12<1>, but the circuit-breaker is operated only if the beam 3<1> of tube 2<1> energizes the cell 11<1>, which it is arranged to do if the fault is internal. With external faults the beam 31 is arranged to deflect in the same direction as 3, so 11<1> is not energized. The quantity measured by the deflection is the reciprocal of the line impedance, since the deflection is proportional to the field at 5, that is, to the line current, and inversely proportional to the line voltage. A graded impedance-time lag arrangement may be provided by means of a number of cells each controlling a relay. Rectifying and smoothing may be avoided by arranging for the A.C. voltage to be impressed directly on the tube, in which case the alternating field created by the network current upsets the deflection as the current is normally out of phase with the line voltage ; accordingly its phase is adjusted by an amount which is equal and opposite to the average phase angle between current and voltage, thereby reducing the alternating to the continuous current state. In Fig. 2, a screen 20, perforated at 21, is made of the same potential as, or of slightly negative potential with respect to, the anode, so that normally the rays 3 cannot strike the collector 22. On fault, the resistance 23 is traversed by current and the resulting p.d. across its ends is used to trip a breaker either directly or, after previous amplification, by polarizing the grid of a discharge tube. The latter arrangement permits amplification in the tube itself, by making the collector 22 of a material having strong secondary emissions.