Minimum size, integral, a.c. overload current sensing, remote power

Abstract

An A.C. overload current sensing, remote power controller of minimum size and weight and integral construction. Current rate sensing wound toroids are used that are small enough to fit around the line terminal studs without having to enlarge the prior insulator space available therein. The electronic overload current detecting and tripping control circuit is replaced by a pair of modules, detector and control modules, having improved performance and a shape and size such that they fit within the relay housing alongside its operating magnet. The detector module has integrator means for converting current rate of change signals into current magnitude indicative signals thereby enabling use therewith of rate sensing wound toroids of about one-tenth the size of equivalent current transformer wound toroids. It fully meets the calibrated step function overload trip time requirements while also providing protection for unusual overload conditions such as varying overloads including pulse accumulation effects or repetitive reset, and simulates the response of a thermal element to prevent excess heating of the wire or load that it is protecting under any overload conditions. Moreover, one version of the control module incorporates a single standard CMOS IC logic element that provides a digital solution to the combinations of control conditions requirements while at the same time reducing the number of conventionally-required cutthroat contacts from two to one and isolating the control input from the relay power circuit. Another version provides reset lockout.