Transverse Differential Reed Switch Protection Without Current and Voltage Transformers for Double-Circuit Lines

This paper considers a principle for constructing transverse differential protection of two parallel 6–35 kV power transmission lines on the supply side, previously proposed by the authors and protected by a patent. Its implementation makes it possible to identify the damaged line without using current and voltage transformers, by employing signals from reed switches installed near the corresponding phases of the lines. The principle is based on monitoring the difference in magnetic field inductions produced by the currents in these phases and determining the damaged line according to the sequence of reed switch actuations. Based on experimental studies of the temporal characteristics of reed switches and on simulation of magnetic fields around the line phases, methodologies for selecting protection operating parameters and for evaluating its sensitivity, taking into account the influence of errors and currents in the phases of both lines, have been developed; the field of application of the protection, the cascade zone, and the locations for installing the reed switches have been determined. It is shown that the calculated cascade zone of the proposed protection can be up to 20% shorter than that of both the traditional protection and a similar reed-switch-based protection. At the same time, in comparison with the latter, implementation of the considered principle requires three times fewer reed switches. The elimination of current and voltage transformers, as shown by the calculations, creates prerequisites for reducing the resource intensity of the protection.