GB1058181A - Improvements in or relating to earth leakage protective devices - Google Patents

Abstract

1,058,181. Protective arrangements. ANDERSON MAVOR Ltd. Aug. 15, 1963 [May 25. 1962; March 9, 1963; May 15, 1963], Nos. 20119/62; 9462/63 and 19229/63. Heading H2K. An earth-leakage protective and lock-out arrangement comprises a transductor having control windings C1, C2 and balancing windings C3, C4 separately connected to the supply lines, a bias winding C6, A.C. operating windings L1, L2 in series with relay means REL1, REL2 controlling a contactor operating circuit or a circuit-breaker tripping circuit, and a lock-out winding C5 energized on the closing of a switch S1 when the contactor or circuitbreaker is opened. In the arrangement shown, under normal conditions, the effect of the control windings C1, C2 is cancelled by the balancing windings C3, C4, lock-out winding C5 is not energized and the effect of the bias winding C6 is such that sufficient current flows in the winding L1, L2 to energize the relay REL1 which completes the contactor operating circuit. Should an earth fault occur, the leakage current to earth through impedances Z1 .. Z3, rectifier B1 and the control windings C1 C2 unbalances the windings C1, C2 and C3, C4 and the resulting modification of the flux in the transductor core causes a reduction in the current through the windings L1, L2 so that the relay REL1 opens the contactor operating circuit. On the opening of the contactor, switch S1 closes so that D.C. flows from a rectifier B3 through the lock-out winding C5, switch S1, balancing winding C4, rectifier B2, impedances Z4 ... Z6 returning via impedances Z1 . . . Z3, rectifier B1 and control winding C2. If no earth fault exists, the currents in windings C4. C2 balance and the current in winding C5 is balanced by the increased current flowing in the bias winding due to the closing of a switch S2. Should an earth fault exist some current in the lock-out circuit will return through the fault path so unbalancing the effects of the windings C2, C4 and increasing the current in the winding C5. This results in an increase of the current through windings L1, L2 and relay REL2 is sufficiently energized to open its contacts in the contactor operating circuit to prevent the closing of the circuitbreaker. In a modified arrangement, Fig. 2 (not shown), the lock-out winding is directly connected to the supply lines through starconnected impedances and auxiliary switches. Each of these arrangements may be provided with a further relay having operating windings connected in series with the control windings C1, C2 and responding to an increase in voltage on the supply lines due to a faulty supply transformer to open contacts in the contactor operating circuit, Figs. 3 and 4 (not shown). The rectifiers may be, or include, Zener diodes.