Optical apparatus for measuring current in a grounded metal-clad installation

In a current transformer designed to equip an electrical installation of the grounded metal-clad type including at least one cylindrical metal cladding filled with dielectric gas and containing at least one conductor disposed parallel to the axis of the cladding, the transformer being of the Faraday-effect type and including, for each conductor, an optical fiber surrounding the conductor, said fiber being connected to an auxiliary optical interface for injecting at least one input light wave into the fiber, and for processing the output light waves, wherein said current transformer includes a support in the form of a disk having its plane perpendicular to said axis and having a periphery in contact with a cross-section inside the cladding, said disk having at least one opening, said at least one conductor passing through, said disk opening including a groove inside said opening, said optical fiber being placed in said groove with, the optical fiber going at least once around said conductor, and having two ends thereof connected to aid associated optical interface disposed outside said cladding, the improvement comprising, a gastight passage extending exteriorly of the cladding, and an enclosure coupled to an end of said gastight passage means remote from said cladding, said optical interface being placed in an enclosure, and communicating via said gastight passage to the interior of said cladding and about said two optical fiber ends passing through said gastight passage and being connected to said optical interface within said enclosure, and wherein said gastight passage includes means within said gastight passage, between said enclosure and said cladding, for limiting heat exchange by conduction and by convection.