Electrical circuit protection devices comprising conductive liquid

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.