Time Delayed Derived Earth Fault Protection (51N); Current Protection: Measured Earth Fault (50G, 51G); Instantaneous Measured Earth Fault Protection (50G); Figure 3-14 Logic Diagram: Derived Time Delayed Earth Fault Protection - Siemens 7SR105 Rho User Manual

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-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
Gn 51N- n Element
Enabled
EF In
Inhibit 51N - n
I
A
I
B
I
C

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:
Fundamental Frequency RMS current:

3.5.1 Instantaneous Measured Earth Fault Protection (50G)

Two instantaneous measured earth fault elements are provided in the 7SR105 Rho Motor Protection Relay.
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
©2018 Siemens Protection Devices
51N-1, 51N-2
A binary or virtual input.
Gn 51N- n Setting
Gn 51N- n Charact
Gn 51N- n Time Mult
&
Gn 51N-n Delay (DTL)
Gn 51N- n Min. Op . Time
Gn 51N- n Follower DTL
Gn 51N- n Reset
En.
I
N
En.
51G/50G Measurement = RMS
51G/50G Measurement = Fundamental
50G-1, 50G-2
A binary or virtual input.
7SR105 Rho Description of Operation
Pickup General Pickup
trip
51N-n
Chapter 1 Page 36 of 57