ABB RET670 Applications Manual page 436

Section 3
IED application
430
Switch onto fault logic
In case of energizing a faulty object there is a risk of having a long fault clearance
time, if the fault current is too small to give fast operation of the protection. The switch
on to fault function can be activated from auxiliary signals from the circuit breaker,
either the close command or the open/close position (change of position).
This logic can be used to issue fast trip if one breaker pole does not close properly at a
manual or automatic closing.
SOTF and Under Time are similar functions to achieve fast clearance at asymmetrical
closing based on requirements from different utilities.
The function is divided into two parts. The SOTF function will give operation from
step 2 or 3 during a set time after change in the position of the circuit breaker. The
SOTF function has a set time delay. The Under Time function, which has 2
restrain blocking, will give operation from step 4. The 2nd harmonic restrain will
prevent unwanted function in case of transformer inrush current. The Under Time
function has a set time delay.
Below the settings for switch on to fault logics are described.
SOTF operation mode: This parameter can be set: Disabled/SOTF/Under Time/SOTF
+Under Time.
SOTFSel: This setting will select the signal to activate SOTF function; CB position open/
CB position closed/CB close command.
tSOTF: Time delay for operation of the SOTF function. The setting range is 0.000 -
60.000 s in step of 0.001 s. The default setting is 0.100 s
StepForSOTF: If this parameter is set on the step 3 pickup signal will be used as
current set level. If set disabled step 2 pickup signal will be used as current set level.
t4U: Time interval when the SOTF function is active after breaker closing. The setting
range is 0.000 - 60.000 s in step of 0.001 s. The default setting is 1.000 s.
ActUndrTimeSel: Describes the mode to activate the sensitive undertime function. The
function can be activated by Circuit breaker position (change) or Circuit breaker
command.
tUnderTime: Time delay for operation of the sensitive undertime function. The setting
range is 0.000 - 60.000 s in step of 0.001 s. The default setting is 0.300 s
Transformer application example
Two main cases are of interest when residual overcurrent protection is used for a power
transformer, namely if residual current can be fed from the protected transformer
winding or not.
1MRK504116-UUS C
nd
harmonic
Application manual