ABB REG670 - Page 378

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 start 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 start
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-discordance 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
HarmResSOFT
ActUnderTime
t4U
AN D
t
tUnderTime
OR
Open
Closed
Close command
ActivationSOTF
t4U
StepForSOTF
STIN2
STIN3
AN D
t
tSOTF
AN D
BLOCK
2nd Harmonic
AN D
Open
Close
Close command
STIN4
SOTF
SOTF or
UnderTime
TRIP
OFF
OR
UnderTime
SOTF
OperationMode
IEC06000643-4-en.vsd
IEC06000643 V4 EN
Figure 168: Simplified logic diagram for SOTF and Under-Time features
EF4PTOC Logic Diagram Simplified logic diagram for the complete EF4PTOC
function is shown in figure 169:
Section 8 1MRK502052-UEN B
Current protection
372
Technical manual