Siemens 7SR18 Solkor - Current Protection: Under-Current (37 & 37 G); Figure 3.8-1 Logic Diagram: Phase Current Inputs Undercurrent Detector (37); Figure 3.8-2 Logic Diagram: Earth Current Inputs Undercurrent Detector (37 G)

7SR18 Description Of Operation
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3.8 Current Protection: Under-Current (37 & 37G)
Two under-current elements are provided 37-1 & 37-2 for phase currents and two are provided 37G-1 & 37G-2
for the earth fault.
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, when either any or all phases have operated depending
upon setting.
An output is also given to indicate the operated phase.
All under-current elements work with True RMS currents.
Operation of the under-current elements can be inhibited from:
Inhibit 37-n A binary or virtual input.
37U/I Guard Setting 0.05, 0.1..5xIn
Figure 3.8-1 Logic Diagram: Phase Current Inputs Undercurrent Detector (37)
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Figure 3.8-2 Logic Diagram: Earth Current Inputs Undercurrent Detector (37G)