Siemens 7SR242 - Current Protection: Phase Overcurrent (51, 50); Instantaneous Overcurrent Protection (50); Figure 3-5 Logic Diagram: Instantaneous Over-Current Element

7SR242 Duobias Description Of Operation
©2010 Siemens Protection Devices Limited Chapter 1 Page 25 of 52
3.2 Current Protection: Phase Overcurrent (51, 50)
The optional phase overcurrent elements have a common setting to measure either fundamental frequency RMS
or True RMS current:
True RMS current: 51/50 Measurement = RMS
Fundamental Frequency RMS current: 51/50 Measurement = Fundamental
3.2.1 Instantaneous Overcurrent Protection (50)
Optionally two instantaneous overcurrent elements are provided, each can be selected to either winding 1 or
winding 2.
Each instantaneous element (50-n) has independent settings. 50-n Setting for pick-up current and 50-n Delay
follower time delay. The instantaneous elements have transient free operation.
Operation of the instantaneous overcurrent elements can be inhibited from:
Inhibit 50-n A binary or virtual input.
50-n Inrush Action: Inhibit Operation of the inrush detector function.
Inhibit 50-n
50-n
50-n Setting
c
50-n
Enabled
Disabled
>
c
50-n Delay
>
c
>
c
Wn-IL1
Wn-IL2
Wn-IL3
50/51
Measurement
L1 81HBL2
50-n Inrush
Action
Off
Inhibit
&
L2 81HBL2
L3 81HBL2
&
&
1
General Pickup
&
1
Figure 3-5 Logic Diagram: Instantaneous Over-current Element