ABB Relion 670 Series Technical Reference Manual page 416

Section 7
Current protection
BLOCK
I
OP
Use_PUValue
Pickup1>
Pickup2>
Pickup3>
Pickup4>
ANSI13000015 V1 EN
Figure 209: Simplified logic diagram for 2nd harmonic blocking feature and Block for Parallel Transformers feature
7.4.2.9
410
Extract second
harmonic current
component
Extract
fundamental
current component
2ndHarmStab
|I |
OP
a
b
Switch on to fault feature
Integrated in the four step residual overcurrent protection are Switch on to fault logic
(SOTF) and Under-Time logic. The setting parameter SOTF is set to activate either
SOTF or Under-Time logic or both. When the circuit breaker is closing there is a risk
to close it onto a permanent fault, for example during an autoreclosing sequence. The
SOTF logic will enable fast fault clearance during such situations. The time during
which SOTF and Under-Time logics will be active after activation is defined by the
setting parameter t4U.
The SOTF logic uses the pickup signal from step 2 or step 3 for its operation, selected
by setting parameter StepForSOTF. The SOTF logic can be activated either from
a
a>b
0.07*IBase
b
a
a>b
b
a
a>b
b
X
OR
0-70ms
0
BlkParTransf=On
a>b
1MRK505222-UUS C
AND
-1
q
2ndH_BLOCK_Int
OR
AND
ANSI13000015-1-en.vsd
Technical reference manual