Chapter 1) 7SR242 Duobias Description Of Operation
©2015 Siemens Protection Devices Limited
Chapter 1 Page 30 of 60
3.3
Current Protection: Derived Earth Fault (50N, 51N)
The earth current is derived by calculating the sum of the measured line currents. These optional elements utilise
RMS current values of the fundamental frequency (50 or 60Hz).
3.3.1 Instantaneous Derived Earth Fault Protection (50N)
Optionally two instantaneous derived earth fault elements are provided, each can be selected to either winding 1
or winding 2.
Each instantaneous element has independent settings for pick-up current
50N-n Setting
and a follower time
delay
50N-n Delay
. The instantaneous elements have transient free operation.
Operation of the instantaneous earth fault elements can be inhibited from:
Inhibit 50N-nt
A binary or virtual input.
50N-n Inrush Action: Inhibit
Operation of the inrush detector function.
User Inhibit
Reylogic (graphical logic).
Figure 3-7
Logic Diagram: Instantaneous Derived Earth Fault Element
Summary of Contents for 7SR242 Duobias
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