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•
Sector
This mode is used with networks earthed with a small
resistance. In this context "small" means, that a fault current
may be more than the rated phase currents. The trip area has a
shape of a sector as drawn in Figure 3.17. The base angle is
usually set to zero degrees or slightly on the lagging inductive
side (i.e. negative angle).
•
Undir
This mode makes the stage equal to the undirectional stage I
The phase angle and U
the amplitude of the selected I
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
alternatives to measure current peaks to detect short restriking
intermittent earth faults:
•
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 (to pick up), but will
not cause trip. When starting happens often enough, such
intermittent faults can be cleared using the intermittent time setting.
The mode should be Undir. The phase angle detection of I
directional mode is insecure.
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.
Two independent stages
There are two separately adjustable stages: Iϕ> and Iϕ>>. Both the
stages can be configured for definite time delay (DT) or inverse time
delay operation time.
Protection Functions
amplitude setting are discarded. Only
0
input is supervised.
0
for rigidly and low impedance earthed
+ I
+ I
= 3I
.
L2
L3
0
ϕ> have two more input signal
.
01
.
02
3-25
>.
0
in
0
or I
a
01Peak
02Peak
857-UM001A-EN-P – July 2009
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