초록 ▼

Electrical circuit protection arrangements with PTC devices and mechanical switches. The combinations of this invention permit the use of mechanical switches and PTC devices to switch voltages and currents in normal circuit operations, wherein the voltage and/or current ratings of the mechanical swi

Electrical circuit protection arrangements with PTC devices and mechanical switches. The combinations of this invention permit the use of mechanical switches and PTC devices to switch voltages and currents in normal circuit operations, wherein the voltage and/or current ratings of the mechanical switches and PTC devices are much less than the normal operating voltages and currents of the circuits. This feature permits the use of smaller and less expensive mechanical switches and PTC device than would otherwise be required in such circuits. The arrangements of switches and PTC devices also permit the PTC devices to limit the magnitude of the fault current passed to the circuit.

대표청구항 ▼

[ What is claimed is:] [8.] An electrical protection system which can be connected between an electrical power supply and an electrical load to form an operating circuit, and which when so connected protects the circuit from overcurrents, which system comprises:a. a circuit interruption element havi

[ What is claimed is:] [8.] An electrical protection system which can be connected between an electrical power supply and an electrical load to form an operating circuit, and which when so connected protects the circuit from overcurrents, which system comprises:a. a circuit interruption element having(1) a normal state which permits the flow of a normal current, I.sub.NORMAL, and(2) a fault state which permits the flow of at most a reduced current, substantially less than I.sub.NORMAL ;b. a control element which(1) is connected in series with the circuit interruption element;(2) has a variable resistance which(a) is low compared to the load when the current in the circuit is the normal current, I.sub.NORMAL, and(b) increases substantially when the current in the load substantially exceeds the normal current, I.sub.NORMAL ;(3) comprises a comparator which compares(a) the current, I.sub.CONTROL, in the control element at a control comparison point, and(b) the current, I.sub.LOAD, in the load at a load comparison point, and(4) changes the circuit interruption element from its normal state to its fault state when I.sub.CONTROL differs from I.sub.LOAD by more than a predetermined current imbalance value, I.sub.DIFF ; andc. a bypass element which(1) is connected in parallel with the control element, and(2) has a resistance such that(a) when the circuit current is I.sub.NORMAL, the ratio of the resistance of the bypass element to the resistance of the control element is such that I.sub.CONTROL differs from I.sub.LOAD by less than I.sub.DIFF, and(b) when the circuit current exceeds I.sub.NORMAL by a predetermined current amount, the ratio of the resistance of the bypass element to the resistance of the control element is such that I.sub.CONTROL differs from I.sub.LOAD by more than I.sub.DIFF.