Functions
82
7UM62 Manual
C53000-G1176-C149-3
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.
Tripping
Characteristic
This result shows that for an internal fault I
diff
= I
stab
. Thus the characteristic of internal
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
) 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
>>”.
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
diff
and I
stab
are compared by the differential protection with the
operating characteristic according to Figure 2-36. If the quantities result into a locus in
the tripping area, a trip signal is given.
1
2
3
4
5
6
7
8
9
10 11 12
13 14 15 16 17 18
1
2
3
4
5
6
7
8
9
10
2041
SLOPE 1
2043
SLOPE 2
2031
I DIFF>>
2021
I DIFF>
2044
BASE POINT 2
BASE POINT 1
2042
Trip area
Add-on stabilization
a
b
c
d
I
diff
I
N
---------
I
stab
I
N
------------
Fault characteristic
Block area
Saturation
d