Technical description
2 Protection functions
2.11 Earth fault protection I0>
(50N/51N)
VM259.EN007
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93
(IDMT). The other stages have definite time operation
characteristic. By using the definite delay type and setting the
delay to its minimum, an instantaneous (ANSI 50N) operation
is obtained.
Using the directional earth fault stages (chapter 2.10) in
undirectional mode, two more stages with inverse operation
time delay are available for undirectional earth fault
protection.
Inverse operation time (I
0
> stage only)
Inverse delay means that the operation time depends on the
amount the measured current exceeds the pick-up setting. The
bigger the fault current is the faster will be the operation.
Accomplished inverse delays are available for the I
0
> stage.
The inverse delay types are described in chapter 2.24. The
device will show a scaleable graph of the configured delay on
the local panel display.
Inverse time limitation
The maximum measured secondary residual current is 10xI
0n
and maximum measured phase current is 50xI
n
. This limits the
scope of inverse curves with high pick-up settings. See chapter
2.24 for more information.
Setting groups
There are two settings groups available for each stage.
Switching between setting groups can be controlled by digital
inputs, virtual inputs (mimic display, communication, logic)
and manually.
Parameters of the undirectional earth fault stage
I
0
> (50N/51N)
Parameter
Value
Unit Description
Note
Status
-
Blocked
Start
Trip
Current status of the stage
F
F
TripTime
s
Estimated time to trip
SCntr
Cumulative start counter
Clr
TCntr
Cumulative trip counter
Clr
SetGrp
1 or 2
Active setting group
Set
SGrpDI
-
DIx
VIx
LEDx
VOx
Digital signal to select the
active setting group
None
Digital input
Virtual input
LED indicator signal
Virtual output
Set