ABB Relion 670 Series RES670, Technical Manual

Page: 216 / 888

parameter SOTFSel can be set for activation of CB position open change, CB position
closed change or CB close command. In case of a residual current pickup from step 2 or
3 (dependent on setting) the function will give a trip after a set delay
tSOTF . This delay is
normally set to a short time (default 200 ms).
The Under-Time logic always uses the pickup signal from the step 4. The Under-Time
logic will normally be set to operate for a lower current level than the SOTF function. The
Under-Time logic can also be blocked by the 2
nd
harmonic restraint feature. This enables
high sensitivity even if power transformer inrush currents can occur at breaker closing.
This logic is typically used to detect asymmetry of CB poles immediately after switching
of the circuit breaker. The Under-Time logic is activated either from change in circuit
breaker position or from circuit breaker close and open command pulses. This selection is
done by setting parameter
ActUnderTime . In case of a pickup from step 4 this logic will
give a trip after a set delay tUnderTime . This delay is normally set to a relatively short time
(default 300 ms). Practically the Under-Time logic acts as circuit breaker pole-
discrepancy protection, but it is only active immediately after breaker switching. The
Under-Time logic can only be used in solidly or low impedance grounded systems.
UNDERTIME
EnHarmRestSOTF
ActUndrTimeSel
t4U
AND
t
tUnderTime
OR
Open
Closed
Close command
SOTFSel
t4U
StepForSOTF
PUST2
PUST3
AND
t
tSOTF
AND
BLOCK
2nd Harmonic
AND
Open
Close
Close command
PUST4
SOTF
Undertime
TRIP
Disabled
OR
Undertime
SOTF
OperationMode
ANSI06000643-4-en.vsd
ANSI06000643 V4 EN
Figure 60: Simplified logic diagram for SOTF and Under-Time features
Section 8
1MRK 511 365-UUS A
Current protection
210 Phasor measurement unit RES670 2.1 ANSI
Technical manual