ABB REL650 Technical Manual page 208

Section 7
Current protection
202
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-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.
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
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).
SOTF
Open
Closed
ActivationSOTF
Close command
STIN2
StepForSOTF
STIN3
BLOCK
UNDERTIME
2nd Harmonic HarmResSOFT
Open
OR
Close
ActUnderTime
Close command
STIN4
IEC06000643 V5 EN-US
Figure 96: Simplified logic diagram for SOTF and under-time features
Simplified logic diagram for the complete EF4PTOC function is shown in Figure
97:
t4U
AND
AND
tUnderTime
AND
t
t4U
AND
Line distance protection REL650 2.2 IEC
1MRK 506 382-UEN A
nd
harmonic restraint
tSOTF
t
SOTF
OFF
SOTF
TRIP
UnderTime
SOTF or
UnderTime
OR
IEC06000643-5-en.vsdx
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Technical manual