The function picks up and trips when the residual current exceeds the set limit. The trip
time characteristic for low stage 51N, 51G and high stage 50N, 50G can be selected to be
either definite time (DT) or inverse definite minimum time (IDMT). The instantaneous
stage 50N-3, 50G-3 always trips with the DT characteristic.
In the DT mode, the function trips after a predefined trip time and resets when the fault
current disappears. The IDMT mode provides current-dependent timer characteristics.
The function contains a blocking functionality. It is possible to block function outputs,
timers or the function itself, if desired.
4.2.1.4
Operation principle
The function can be enabled and disabled with the
Operation
setting. The corresponding
parameter values are “Enable” and “Disable”.
A070437-ANSI V1 EN
Figure 149:
Functional module diagram
Level detector
The operating quantity can be selected with the setting
IG/I0 signal Sel
. The selectable
options are "Measured IG" and "Calculated I0". The operating quantity is compared to the
set
Pickup value
. If the measured value exceeds the set
Pickup value
, the level detector
sends an enable-signal to the timer module. If the
ENA_MULT
input is active, the
Pickup
value
setting is multiplied by the
Pickup value Mult
setting.
The protection relay does not accept the
Pickup value
or
Pickup value
Mult
setting if the product of these settings exceeds the
Pickup value
setting range.
The pickup value multiplication is normally done when the inrush detection function
(INR) is connected to the
ENA_MULT
input.
1MAC059074-MB A
Section 4
Protection functions
615 series ANSI
315
Technical Manual
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