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3.6
50LC/SOTF Switch onto Fault Protection
Overview of the Function (50LC/SOTF)
The instantaneous tripping at Switch onto Fault (SOTF) function serves for immediate tripping when switching
onto a fault.
•
Detects phase faults in the electrical power system immediately after energization
•
Provides additional overcurrent protection at the time of circuit‑breaker closing operation
•
Reports that a fault was present during a close operation
•
Can be used to prevent repeatedly closing a circuit breaker onto a faulty system
•
Can ensure that faults are cleared from the circuit breaker being closed rather than from a remote loca-
tion
The SOTF function monitors the phase current for a maximum duration of 25 AC cycles from the CT interrupt
and trips when any fault is detected as per the user settings. After the 25 AC cycles, the SOTF function is
inhibited automatically.
Structure of the Function (50LC/SOTF)
The switch onto fault protection element has group‑dependent settings. These settings can be different in
each settings group – group numbers (Gn) 1 and 2.
The 50LC/SOTF function monitors the primary system phase currents using the phase CT inputs for example
CT1/2/3.
The 50LC/SOTF element provides additional 3‑phase overcurrent protection that can be set to suit fault detec-
tion during energization of a circuit. Typically, this element is set faster than the time‑graded overcurrent and
earth fault protection to clear faults when the circuit breaker is closed onto a faulted system.
One element is available for this function.
Blocking of the Stage
The 50LC/SOTF function can be disabled if it is not required.
Each element has an inhibit input that can be operated by a binary input or by an inrush current detected by
the 81HBL2 element.
Reyrolle, 7SR46 Device, Manual
C53000-G7040-C103-1, Edition 10.2022
3.6 50LC/SOTF Switch onto Fault Protection
Functions
55
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