US 5,471,185 AGranted

Electrical circuit protection devices comprising conductive liquid compositions

AssigneeEaton Corporation

InventorsJohn J. Shea, James D. B. Smith, Karl F. Schoch, Jr.

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Abstract

The invention provides an electrical circuit protection device using a conductive liquid contained in a flexible tube contacted and sealed at each end by an annular metal electrode capped by a flexible membrane. The flexible tube is further sealed inside a solid insulating tube which contains a ferromagnetic liquid. The ferromagnetic liquid surrounds the flexible tube and remains in intimate contact with the outside of the flexible tube and is connected to a load sensing element which generates a magnetic field in the ferromagnetic fluid in response to excessive currents applied in the current path through the conductive liquid between the electrodes. This assembly is contained inside a tubular resistor. Under normal current conditions, a current flows through the conductive liquid which has relatively low resistivity. Upon a fault condition, a self generated magnetic field from the fault current causes the ferromagnetic fluid to rapidly constrict and pinch off current flow in the conductive liquid by constricting the current path in the liquid through deformation of the flexible capsule, i.e., by radial contraction and axial expansion. The current is then preferably commutated to the cylindrical resistor to limit the let through current to a safe value. Once the fault is limited, the magnetic field is dissipated and the flexible membranes force the conductive liquid and ferromagnetic fluid back to its their original position and the conductive liquid accordingly automatically reverts back to low resistivity for normal current conduction.

Claims31

Dependent claims

An electrical circuit protection device, which comprises:

(a) an elongated flexible capsule having a length and two ends;
(b) an effective amount of a conductive liquid composition contained within the flexible capsule between the two ends, the conductive liquid being capable of carrying an applied current and switching the current path therein from conductivity to resistivity when subject to an effective amount of constriction transverse to the length of the flexible capsule and transverse to the direction of the electrical current applied to the conductive liquid;
(c) two electrodes having an annulus substantially surrounding the two ends of the flexible capsule, the two electrodes being electrically connected to the conductive liquid composition and electrically connectable to a source of electrical power to cause a current to pass through the conductive liquid composition, and each annulus of the two electrodes being sealed by a flexible membrane;
(d) an elongated insulating housing having a length and two ends, the housing containing the flexible capsule, the housing being closed at both ends by the two sealed electrodes;
(e) an effective amount of a magnetizable fluid composition contained within the housing and generally surrounding the flexible capsule, the magnetizable fluid being electromagnetically connected to the two electrodes;
and,
(f) an elongated resistor having a length and two ends, the resistor generally surrounding the insulating housing and electrically connected to the two electrodes,
in which an excessive current when applied to the electrical circuit protection device generates a magnetic field transverse to the direction of the applied current flowing through the conductive liquid composition along the length of the flexible capsule causing the ferromagnetic fluid to redistribute and deform the flexible capsule by transverse contraction and axial expansion to cause a switching of the current path through the conductive liquid between the electrodes from conductivity to resistivity and a commutating of the excessive current to the resistor to effectively limit the let through current to a safe value.

5 more elements

An electrical circuit, which comprises:

(a) an electrical power source having a voltage;
(b) an electrical load;
and,
(c) an electrical circuit protection device, which comprises:
(i) an elongated elastomeric flexible capsule having a length and two ends;
(ii) a conductive liquid composition contained within the flexible capsule between the two ends, the conductive liquid being capable of carrying an applied current and switching the current path therein from conductivity to resistivity when subject to an effective amount of constriction transverse to the length of the flexible capsule and to the direction of an electrical current applied to the conductive liquid;
(iii) two metal or alloy electrodes having an annulus and substantially surrounding the two ends of the flexible capsule, the two electrodes being electrically connected to the conductive liquid and electrically connected to the power source of electrical power and the load to cause a current to pass through the conductive liquid from the power source to the load, and each annulus of the two electrodes being sealed by an elastomeric flexible membrane;
(iv) an elongated insulating housing having a length and two ends, the housing containing the flexible capsule, the housing being closed at both ends by the two electrodes;
(v) a ferromagnetic fluid composition contained within the housing and generally surrounding the flexible capsule, the ferromagnetic fluid being electromagnetically connected to the two electrodes;
and,
(v) an elongated shunt resistor having a length and two ends, the resistor generally surrounding the insulating housing and electrically connected to the two electrodes,
in which a trip current when applied to the electrical circuit generates a magnetic field transverse to the direction of the applied current flowing through the conductive liquid causing the ferromagnetic fluid to redistribute and deform the flexible capsule by transverse contraction and axial expansion to cause a switching of the conductive path through the conductive liquid from conductivity to resistivity and a commutating of the trip current to the shunt resistor to effectively limit the let through current to a safe value.

9 more elements

Dependencies are inferred from the claim text.