7SR105 Rho Description of Operation
©2018 Siemens Protection Devices Chapter 1 Page 37 of 57
I
G
&
50G-n
General Pickup
Enabled
Disabled
Gn
50
G-
n Element
EF In
Inhibit 50
G-
n
50
G Measurement
>
En
Gn 50G- n Setting
Gn
50G- n Delay
Figure 3-15 Logic Diagram: Measured Instantaneous Earth-fault Element
3.5.2 Time Delayed Measured Earth Fault Protection (51G)
Two instantaneous measured earth fault elements are provided in the 7SR105 Rho Motor Protection Relay.
51G-1, 51G-2
51G-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 51G-n Char. A time multiplier is applied to the characteristic curves
using the 51G-n Time Mult setting. Alternatively, a definite time lag (DTL) can be chosen using 51G-n Char.
When DTL is selected the time multiplier is not applied and the 51G-n Delay (DTL) setting is used instead.
The 51G-n Reset setting can apply a definite time delayed reset or when the operation is configured as an IEC
or ANSI curves 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 51G-n Min. Operate Time setting.
A fixed additional operate time can be added to the characteristic using 51G-n Follower DTL setting.
Operation of the time delayed measured earth fault elements can be inhibited from:
Inhibit 51G-n A binary or virtual input.
I
G
&
Enabled
Disabled
Gn 51G- n Element
EF In
Inhibit 51G
-n
51 G Measurement
General Pickup
51G-n
Gn 51G- n Setting
Gn 51G
- n Charact
Gn 51G- n Time Mult
Gn 51G- n Delay ( DTL)
Gn 51G- n Reset
En.
Gn 51G-
n Follower DTL
Gn 51G
- n Min. Op.
Time
En.
Pickup
trip
Figure 3-16 Logic Diagram: Measured Time Delayed Earth Fault Element (51G)
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