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7SR105 Rho Description of Operation
©2018 Siemens Protection Devices Chapter 1 Page 33 of 57
3.2 Current Protection: Undercurrent (37)
Two rms measuring under-current elements are provided.
Each phase has an independent level detector and current-timing element.
Gn 37-n Setting
sets the pick-up
current. An output is given after elapse of the
Gn 37-n Delay
setting.
Operation can be selected for any phase or all phases using
Gn 37-n Start Option
Operation of the under-current elements can be inhibited from:
Inhibit 37-n
A binary or virtual input
Gn 37-n U/C Guarded
Operation of the undercurrent guard function
<
<
<
<
&
<
<
&
Inhibit 37-n
&
Enabled
Gn 37-n Element
Yes
Gn 37-n U/C
Guarded
Gn 37-n U/C Guard
Setting
I
A
I
B
I
C
Gn 37-n Setting
En
37-n
General Pickup
Gn 37-n Delay
Gn 37 Start
Option
Figure 3-10 Logic Diagram: Undercurrent Detector (37)
3.3 Current Protection: Phase Overcurrent (50, 51)
All phase overcurrent elements have a common setting for the 50 elements and 51 elements to measure either
the fundamental frequency RMS or True RMS current:
True RMS current: 50 Measurement = RMS, 51 Measurement = RMS
Fundamental Frequency RMS current: 50 Measurement = Fundamental, 51 Measurement = Fundamental
3.3.1 Instantaneous Overcurrent Protection (50)
Two Instantaneous overcurrent elements are provided in the 7SR105 Rho Motor Protection Relay.
50-1, 50-2
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.
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