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

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
50-n Inrush Action: Inhibit
User Inhibit
50-n Element
Disabled
Enabled
Inhibit 50-n
User Inhibit 50-n
50-n Inrush
L1 81HBL2
Action
Off
Inhibit
L2 81HBL2
L3 81HBL2
Wn-IL1
Wn-IL2
Wn-IL3
Figure 3-5
©2015 Siemens Protection Devices Limited
A binary or virtual input.
Operation of the inrush detector function.
Reylogic (graphical logic).
&
50-n Setting
Enable
& c
&
c
c
&
50/51
Measurement
Logic Diagram: Instantaneous Over-current Element
Chapter 1) 7SR242 Duobias Description Of Operation
50-n Delay
>
>
>
General Pickup
1
50-n
1
Chapter 1 Page 28 of 60