ABB REG670 - Switch on to Fault Feature

a
b
a>b
BLOCK
AND
I
OP
Extract second
harmonic current
component
Extract
fundamental
current component
X
2ndHarmStab
a
b
a>b
a
b
a>b
0.07*IBase
IEC13000015-3-en.vsd
UseStartValue
IN1>
IN2>
IN3>
IN4>
a
b
a>b
t
t=70ms
OR
AND
BlkParTransf=On
q
-1
OR
2ndH_BLOCK_Int
q
-1
= unit delay
IEC13000015 V3 EN
Figure 167: Simplified logic diagram for 2nd harmonic blocking feature and Block for Parallel Transformers
feature
8.4.7.10 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 start signal from step 2 or step 3 for its operation, selected by
setting parameter StepForSOTF. The SOTF logic can be activated either from change
in circuit breaker position or from circuit breaker close command pulse. The setting
parameter ActivationSOTF can be set for activation of CB position open change, CB
position closed change or CB close command. In case of a residual current start from
1MRK502052-UEN B Section 8
Current protection
371
Technical manual