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Functions
Tripping
Characteristic
82
The stabilizing quantity is calculated from the arithmetic average of a rectified quantity,
so that the filter effect is less for it. As a result, the stabilization component in
interference components, especially aperiodic DC components, will be higher than
their differential current.
This result shows that for an internal fault I
faults in the tripping diagram (see Figure 2-36) is a straight line with a slope of 45°.
Figure 2-36 shows the complete operation characteristic of the 7UM62. Branch a
represents the sensitivity threshold of the differential protection (setting
I-DIFF>) and considers constant error currents such as magnetizing currents.
Branch b considers current-proportional errors which may result from transformation
errors of the main CTs or the input CTs of the relay, or which may be caused by
mismatching or by the influence of tap changers in transformers with voltage control.
In the range of high currents which may give rise to current transformer saturation,
branch c provides for additional stabilization.
In the presence of differential currents above branch d a trip command is issued
regardless of the stabilizing current and the harmonic stabilization. This is the
operating range of the "High-Speed Trip Stage I
I
diff
-------- -
10
I
N
9
8
2031
I DIFF>>
7
6
5
4
3
2
b
1
2021
a
I DIFF>
1
2
3
2044
BASE POINT 2
2042
BASE POINT 1
Figure 2-36
Operating Characteristic of the Differential Protection
The area of add-on stabilization is determined by the saturation indicator (see side
title "Add-on Stabilization During Current Transformer Saturation".
The currents I
and I
diff
stab
operating characteristic according to Figure 2-36. If the quantities result into a locus in
the tripping area, a trip signal is given.
= I
diff
Fault characteristic
Trip area
4
5
6
7
8
9
are compared by the differential protection with the
. Thus the characteristic of internal
stab
>>".
Diff
Block area
2043 SLOPE 2
c
2041 SLOPE 1
Add-on stabilization
Saturation
10 11 12 13 14 15 16 17 18
C53000-G1176-C149-3
d
d
I
stab
----------- -
I
N
7UM62 Manual
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