Switch onto fault protection
During switch onto fault condition i.e. when breaker is closed into existing fault,
earth-fault current estimate may be disturbed by the inrush currents of energized
transformers. Therefore, IFPTOC includes a dedicated switch onto fault (SOTF) logic
module. SOTF-functionality provides dedicated fault detection and tripping in case
feeder breaker is closed into earth fault.
Switch onto fault protection module is enabled with setting
Enable SOTF mode
=
“on”. Module is enabled by default.
In case multiple instances of IFPTOC are applied in the protection
configuration, ALL instances of IFPTOC requires SOTF module
functionality to be enabled to provide selective operation during an SOTF
condition.
SOTF condition is declared, if an earth fault is detected (EF_IND = TRUE) within set
SOTF Cond duration
milliseconds from breaker close command (input CB_CL_CMD is
activated).
Indication of detected SOTF condition is declared by activation of ST_SOTF and
START outputs.
Operate time during switch onto fault condition is given with setting SOTF operate
time. OPERATE and OP_SOTF outputs are activated after operation timer has
elapsed.
Figure 359: Illustration of switch onto fault condition and operation of SOTF logic in IFPTOC
1MRS759142 F
Protection functions
REX640
Technical Manual
633
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