Abstract
It is noted that the replacement of current transformers with some other, less metal-intensive and bulky, current sensors is an urgent task in the electric power industry. The advantages and disadvantages of some of these sensors are briefly considered. The advantages of reed switches over other current sensors are given and their operating principle is described. It is stated that on the basis of obtaining information about the current in the phase of an electrical installation from reed switches, a number of short-circuit protections have already been developed. The full resistance measuring body is considered in detail and its operation in the short-circuit and load mode is described. A directional resistance relay is proposed with a simple circuit for test diagnostics of a fault, consisting of a button, a control winding worn on the starting reed switch, two intermediate relays and a current control block in the specified winding. The method of selecting the parameters of actuation of the measuring body is presented and its operation in various modes is described.