Principles of the building of relay protection

The analysis the main characteristic of used relay protection (RP) selectivity is made. The most full realization of this characteristic is proven to have differential protection. On the ground of this reason and analysis of the arc monitoring the short circuits there are formulated two principles of the building RP: usual metric which is used for building all the types existing RP with measuring relays and proposed logical principle, on which is built arc protection, on flash of the electric arc at short circuits (SC). The differential metric principle RP is proved to be the most appropriate for building RP on logical scheme. There are compared factors existing RZ by the approximation to logical principle of the building RP. As special principle of the building RP is distinguished the distance protection. The advantage the logical scheme of the building RZ are discussed in contrast with existing metric.