ABB RED650 - Page 107

5 The interval when IdMinHigh is active is set to 60 s because a power transformer is included in
the protected zone. As both IEDs process the same currents, both must have the same value
set for IdMinHigh .
6
The unrestrained operate (differential) current limit should greater than the highest through fault
current. This current appears at a three-phase short circuit on the 33 kV side of the transformer
and can be calculated as:
220
2.75
3 (7.0 15.0 24.2)
Through
I kA= =
× + +
EQUATION1423 V1 EN-US (Equation 18)
With a safety margin of 20%:
1.2
1.2 2.75 3.30
5.50
0.6 0.6
Through
I
kA kA
Idunre
Ibase kA kA
×
×
= = = =
EQUATION1424 V1 EN-US (Equation 19)
7 The cross-block logic should always be active when there is a power transformer in the
protected zone.
Setting example with a small tap transformer in the protected zone
A typical example is shown in Figure 46
IEC12000193-2-en.vsd
3Id> 3Id>
SA
1700
MVA
SA
1280
MVA
10MVA
ek=10%
138/10kV
3Id>
3Id>
A B
IEC12000193 V2 EN-US
Figure 46: Setting example
Input data to calculation:
• Apparent source power at A side: Ss
A
= 1700 MVA
• Line impedance from A to tap: Zl
A
= 2.8 Ω
• Line impedance from tap to B side: Zl
B
= 1.2 Ω
1MRK 505 393-UEN B Section 6
Differential protection
Line differential protection RED650 2.2 IEC 101
Application manual