ABB RES670 Technical Manual page 216

Section 8
Current protection
210
The SOTF logic uses the pickup signal from step 2 or step 3 for its operation, selected
by setting parameter StepForSOTF. The setting 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 acts as a 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.
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
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).
1MRK 511 408-UUS A
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harmonic restraint feature. This
Phasor measurement unit RES670 2.2 ANSI
Technical manual