Patent GB-1121049-A (GB)
Title: Hybrid semiconductor type d.c. contactor
IPC: H01H33/59
Filed: 1966-12-29
Abstract: 1,121,049. Protective arrangements. COMPAGNIE ELECTRO MECANIQUE. 29 Dec., 1966 [30 Dec., 1965], No. 58061/66. Heading H2K. [Also in Division H1] A contactor supplying a load 1 with D.C. comprises a main mechanical contact 3 and a thyristor 2 connected in parallel with one another, the contact 3 being normally open and operable by an energizing winding 7 which also operates'an auxiliary contact 6 in a quenching circuit for the thyristor 2. The thyristor 2 is quenched by a capacitor 15 discharging therethrough consequent either upon closure of contact 6 or if the load current is excessive. Closure of auxiliary contact 6, e.g. by opening normally closed contact A to de-energize the winding 7 and so allow opening of contact 3, produces discharge of a capacitor 23 through a diode 26, resistance 27 and resistance 28, and causes firing of a thyristor 22, whereafter the gate of a thyristor 21 goes positive and thyristor 21 fires. When thyristor 22 fires, the voltage across capacitor 15 is applied across the circuit formed by diode 20, potentiometer 18 and Zener diode 17, and the voltage across Zener diode 17 is applied to the gate of thyristor 21. Capacitor 15 then discharges into the circuit comprising the thyristor 22, resistance 29, main thyristor 2 and thyristor 21. Capacitor 15 charges up from the D.C. network through resistance 16, Zener diode 17, potentiometer 18 and a resistance 19 shunted by a reverse polarity diode 20. Capacitor 23 charges up through a resistance 24 supplied by a potentiometer 25 connected to the D.C. supply. Brief closure of normally open contact M causes firing of thyristor 2 as a capacitor 10 discharges, having been charged via resistance 11 and a potentiometer 12 connected to the D.C. network. If current is normal the voltage across the circuit comprising load 1 and a winding 9 energizes winding 7 and closes contact 3, short-circuiting the thyristor 2, and opening contact 6 to allow re-charging of capacitor 23 which was short-circuited by firing of thyristor 22. If, however, load current is excessive, the voltage across resistance 29 in series with thyristor 2, and applied via Zener diode 30, diode 31 and resistance 27 to the gate of thyristor 22, fires thyristor 22 and then capacitor 15 discharges through thyristor 2 and quenches it. Normally closed contact 8 is opened by a winding 9 when the current through load 1 reaches a predetermined level, thus forming on overcurrent protective relay. To ensure that thyristor 2 cannot refire, capacitor 10 is connected via diode 32 to the anode of thyristor 22, so that capacitor 10 discharges abruptly. To accelerate closure of the contactor a winding (34) in series with thyristor 2 is wound on the same magnetic circuit as winding 7, (Fig. 2, not shown). In an alternative embodiment, (Fig. 3, not shown), winding 7 has an independent power supply (35) controlled by a selectively operable contact (40) and, as main contact 3 closes, it first closes a contact (36) similar to contact M of Fig. 1, so that capacitor 10 discharges and thyristor 2 is fired. Fig. 4 (not shown), shows another system for charging the quenching capacitor 15, the contactor energizing winding (7) being placed in series between a normally closed stop contact (A) and a normally open starting contact (M).