Abstract: A file drawer having a removable outer drawer head which includes a drawer body and an inner drawer head permanently secured to the drawer body. The drawer body and inner drawer head include retaining means and the removable outer drawer head includes securing means which coact to releasably retain the outer drawer head to the drawer body and the inner drawer head. The removable outer drawer head is retained in such a way as to obviate the need for hardware, tools or additional parts, either in securing or removing the outer drawer head to the drawer body and the inner drawer head.

Abstract: Apparatus for the supervision of a sudden pressure relay (SPR) system which protects a power system network transformer having a plurality of windings associated with each phase of the power system network. This apparatus overcomes the difficulties associated with previous overcurrent supervision of the SPR system for multiple-winding transformers. The apparatus utilizes a maximum restraint signal selection network which offers a discriminating differentiation between high and low current levels in all of the transformer windings and accomplishes this in one embodiment with a single measuring unit per phase of the power system network. For each phase, when the selected maximum restraint signal exceeds a predetermined level, the supervisory unit blocks the SPR from operating the breakers which isolate the power transformer from the power system network. This blocking condition is relieved after a predetermined time period from when the selected restraint signal falls below the predetermined level.

Abstract: A mutual inductance differential current transducer employs a toroidal coil mounted coaxially and generally centrally of the length of an alternating current conductor wiht a conductive sheet therebetween surrounding the conductor and of substantially the same length and in insulated relationship from the conductor. The axial length of the coil is less than approximately one-third the length of the conductor, and the toroidal cross-section has a longer leg parallel to the axis of the conductor and a cross-sectional area eliminating the need for external capacitive and magnetic shielding. The coil is wound with an integer number of layers of the same number of turns per layer, the total number of turns being selected to produce a predetermined range of voltage levels of the analog voltage signal output of the coil, produced in response to and representative of the differential current flow through the conductor.