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Input Signal Selection
Each stage can be connected to supervise any of the following inputs
and signals:
•
Input I
for all networks other than rigidly earthed
01
•
Input I
for all networks other than rigidly earthed
02
•
Calculated signal I
0Calc
networks. I
= I
0Calc
L1
Additionally the stage I
0
measure current peaks to detect a restriking intermittent earth fault:
•
I
to measure the peak value of input I
01Peak
•
I
to measure the peak value of input I
02Peak
Intermittent Earth Fault Detection
Short earth faults make the protection to start (pick up), but will not
cause trip. When starting happens often enough, such intermittent
faults can be cleared using the intermittent time setting.
When a new start happens within the set intermittent time, the
operation delay counter is not cleared between adjacent faults and
finally the stage will trip. By using input signals I
single one-millisecond current peak is enough to start the stage and
increase the delay counter by 20 ms. For example, if the operating
time is 120 ms, and the time between two peaks does not exceed the
intermittent time setting, the sixth peak will cause a trip.
Four or six Independent Undirectional Earth Fault Overcurrent
Stages
There are four separately adjustable earth fault stages: I
I
>>>, and I
>>>>. The first stage I
0
0
time (DT) or inverse time operation characteristic (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 10) in
undirectional mode, two or more stages with inverse operation
time delay are available for undirectional earth fault protection.
Protection Functions
for rigidly and low impedance earthed
+ I
+ I
L2
L3
> have two more input signal alternatives to
01
02
> can be configured for definite
0
3-31
or I
a
01Peak
02Peak
>, I
>>,
0
0
857-UM001A-EN-P – July 2009
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