7SR105 Rho Description of Operation
©2018 Siemens Protection Devices Chapter 1 Page 36 of 57
3.4.2 Time Delayed Derived Earth Fault Protection (51N)
Two time delayed derived earth fault elements are provided in the 7SR105 Rho Motor Protection Relay.
51N-1, 51N-2
51N-n Setting
sets the pick-up current level.
A number of shaped characteristics are provided. An inverse definite minimum time (IDMT) characteristic is
selected from IEC and ANSI curves using
51N-n Char
. A time multiplier is applied to the characteristic curves
using the
51N-n Time Mult
setting. Alternatively, a definite time lag delay (DTL) can be chosen using
51N-n
Char
. When definite time lag (DTL) is selected, the time multiplier is not applied and the
51N-n Delay (DTL)
setting is used instead.
The
51N-n Reset
setting can apply a
definite time delayed
reset
,
or when configured as an IEC or ANSI if the
reset is selected as IEC/ANSI (DECAYING) reset the associated reset curve will be used. The reset mode is
significant where the characteristic has reset before issuing a trip output.
A minimum operate time for the characteristic can be set using the
51N-n Min. Operate Time
setting.
A fixed additional operate time can be added to the characteristic using the
51N-n Follower DTL
setting.
Operation of the time delayed earth fault elements can be inhibited from:
Inhibit 51N-n
A binary or virtual input.
General Pickup
51N-n
Gn 51N- n Setting
Gn 51N- n Charact
Gn 51N- n Time Mult
Gn 51N-n Delay (DTL)
Gn 51N- n Reset
En.
Gn 51N- n Follower DTL
Gn 51N- n Min. Op . Time
En.
Pickup
trip
Inhibit 51N- n
&
Enabled
Gn 51N- n Element
I
N
I
A
I
B
I
C
EF In
Figure 3-14 Logic Diagram: Derived Time Delayed Earth Fault Protection
3.5 Current Protection: Measured Earth Fault (50G, 51G)
The earth current is measured directly via a dedicated current analogue input, IL4.
All measured earth fault elements have a common setting to measure either the fundamental frequency RMS or
True RMS current:
True RMS current:
51G/50G Measurement
= RMS
Fundamental Frequency RMS current:
51G/50G Measurement
= Fundamental
3.5.1 Instantaneous Measured Earth Fault Protection (50G)
Two instantaneous measured earth fault elements are provided in the 7SR105 Rho Motor Protection Relay.
50G-1, 50G-2
Each instantaneous element has independent settings for pick-up current
50G-n Setting
and a follower time
delay
50G-n Delay
. The instantaneous elements have transient free operation.
Operation of the instantaneous measured earth fault elements can be inhibited from:
Inhibit 50G-n
A binary or virtual input.
Summary of Contents for 7SR105 Rho
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