Current Protection: Under-Current (37, 37G & 37Sef); Figure 3.9-1 Logic Diagram: Undercurrent Detector (37, 37G & 37Sef) - Siemens 7SR21 Manual

7SR21 & 7SR22 Argus Description of Operation
3.9 Current Protection: Under-Current (37, 37G & 37SEF)
Two under-current elements are provided for each 37, 37G & 37SEF protection function.
Each phase has an independent level detector and current-timing element. 37-n Setting sets the pick-up current.
An output is given after elapse of the 37-n Delay setting.
Operation of the under-current elements can be inhibited from:
A binary or virtual input, or function key
Inhibit 37-n
Figure 3.9-1 Logic Diagram: Undercurrent Detector (37, 37G & 37SEF)
©2010 Siemens Protection Devices Limited Chapter 1 Page 41 of 71