This section defines how the SEL-451 acts during faults. It covers directional elements, which are crucial for security and sensitivity in complex networks. Understanding negative-sequence directional elements, as described in the manual, ensures reliable detection of high-resistance faults. 2. SELogic Control Equations (Section 4)
: Newer manuals detail the use of TiDL (Time-Domain Link) and Sampled Values (SV) based on IEC 61850, which simplify substation modernization by reducing copper wiring.