Patent GB-801633-A (GB)
Title: Improvements in or relating to electric protective circuit apparatus
Inventor: FIORA MARCEL
IPC: H02H3/093
Filed: 1956-02-03
Abstract: 801,633. Protective cut-out systems. COMPAGNIE POUR LA FABRICATION DES COMPTEURS ET MATERIEL D'USINES A GAZ. Feb. 3, 1956, No. 3448/56. Class 38 (5). An arrangement for overcurrent or over-voltage protection comprises, Fig. 1, a transformer 1 having its primary 2 in the protected circuit and its secondary voltage, regulable by a resitance or potentiometer 4, applied through a rectifier 5 to a condenser 6. Connected across the terminals of condenser 6 are an auxiliary relay 9 in series with a resistance 7 and a condenser 14 in series with a resistance 8, the relay contacts 9a, 9b normally having the positions shown so that contact 9a short-circuits the resistance 7 and contact 9b completes a discharge path for the condenser 14 through a resistance 13. The priming anode and cathode of a cold cathode discharge tube 16 are connected across the condenser 14 through a resistance 15, the load circuit of the tube being supplied from a D.C. source 17 through an auxiliary contact 19 of the protecting circuitbreaker (not shown) and a relay 18 controlling the circuit-breaker trip circuit. On fault, the voltage across condenser 6 operates relay 9 removing the short-circuit from 7 the reduced current through the relay coil 10 being just sufficient to hold the relay operated; also, condenser 14 is progressively charged through resistance 8. Eventually the voltage across the condenser 14 fires the tube 16 and relay 18 is operated from the source 17 to close its contact 18a whereby the protecting circuit-breaker is tripped. This arrangement gives an inverse time-delay since the time for firing of the tube 16 depends on the time constant of circuit 14, 15 which in turn depends on the voltage applied by the transformer 1 and thus on the value of the fault current. Opening of the circuitbreaker restores the parts to this initial condition in readiness for a further operation. In an arrangement for giving a constant time-delay, Fig. 2, a spark gap tube 20, e.g. a neon tube, is connected in series with the relay coil 10 and the terminals of the tube are connected to the circuit comprising condenser 14 and resistance 8. Thus when the voltage across condenser 6 attains a certain value the tube 20 conducts and relay 9 operates and the constant voltage across the tube is applied to circuit 8, 14 to fire tube 16 as in Fig. 1. An additional contact 18b closed by the relay 18 permits part of the current through the relay to by-pass the tube 16. In another arrangement, Fig. 3, the voltage across the resistance 4 is applied to a potentiometer 24, the potentiometer tapping 24a being connected through a protective resistance 25 to the priming anode of a cold cathode discharge tube 22. On fault the tube 22 fires and completes the circuit through the relay coil 10 from the source 17 whereby the voltage of source 17 is applied through the contact 9a to the circuit comprising neon tube 23 and resistance 28, the voltage across tube 23 being applied to the condenser 14 and resistance 8 through the contact 9b, the voltage across condenser 14 being applied to the tube 16 as in the previous embodiments. An oscillatory circuit 26, 27 extinguishes the tube 22 after the protecting circuit-breaker has opened. In a modification of Fig. 3 (Fig. 4, not shown) a third, normallyclosed, contact of the relay 9 completes a circuit from a " low " tapping on the potentiometer 24 to the priming anode of the tube 16 whereby instantaneous tripping of the protecting circuitbreaker occurs on severe overload. Also, an inverse time-delay characteristic may be obtained as in Fig. 1 by manual disconnection of the tube 23. In a 3-phase arrangement (Fig. 7, not shown) transformers 1 connected in the individual phases supply through three parallelconnected rectifier bridges, the potentiometer 24.