Siemens 7SR242 - Current Protection: Derived Earth Fault (50 N, 51 N); Instantaneous Derived Earth Fault Protection (50 N); Figure 3-7 Logic Diagram: Instantaneous Derived Earth Fault Element

7SR242 Duobias Description Of Operation
©2010 Siemens Protection Devices Limited Chapter 1 Page 27 of 52
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.
Figure 3-7 Logic Diagram: Instantaneous Derived Earth Fault Element