GB574077A - Improvements in and relating to thermal relays for protecting electrical conductors,machines and apparatus against overload - Google Patents

Abstract

574,077. Protective cut-out arrangements; thermal switches. AKT.-GES. BROWN, BOVERI, & CIE. Dec. 31, 1943, No. 21916. Covention date, Dec. 31, 1942. [Class 38 (v)] A thermal overload relay employing a mass forming the thermal image of the apparatus to be protected, has a column of oppositelydirected bimetallic plates d in a thermallyinsulating sleeve f<2> around which is looped a striplike heating resistance b energized by a current transformer in the line. Resistance b is spaced by thermally-insulating sleeve f<1> from a metal housing g in which interchangeable heat-storage masses e<2> are supported by an intermediate member u, the whole being enclosed in an insulating hood h supported by poor-conductivity supports on a frame. The base of the column d rests on the support q of an axle i which is rotatable by the expansion of the column so as to throw a lever o overcentre and close trip contacts. The drive includes a differential gear, of which the wheel m has a pointer for setting the desired tripping temperature, whereas the wheel l carries a pointer indicating the temperature of the protected apparatus and may operate a maximum-temperature indicating pointer (not shown). An instantaneous (or retarded) maximum-current electromagnetic relay s making an alternative trip circuit also closes contacts for short-circuiting the heater b, the current in which may be adjusted by a variable shunt r. The elements b, f, g determine the shape of the initial part of the temperature-time curve, whereas the shape of the final part can be varied to suit the particular apparatus by inserting suitable masses e<2>.