Siemens 7SR51 - 50 SOTF Switch Onto Fault; Overview of Functions; Structure of the Function

50SOTF Switch onto Fault
Overview of Functions
The 50SOTF and 50GSOTF protection is used to provide:
•
Detect phase and earth faults in the electrical power system immediately after energization
•
Provides additional overcurrent and earth fault protection at the time of circuit-breaker close operation
•
Reports that a fault was present during a close operation
•
Can be used to prevent repeatedly closing a circuit-breaker onto a faulted system
•
Can ensure that faults are cleared from the circuit-breaker being closed rather than from a remote loca-
tion
Structure of the Function
The switch onto fault function element has group dependent settings. These settings can be different in each
settings group – group numbers (Gn) 1 to 4.
This function corresponds to the logical node SOTFPTOC* and SOTFGPTOC* in IEC 61850.
The 50SOTF function monitors the primary system phase currents using the line CT inputs e.g. CT1/2/3.
The 50GSOTF function monitors the primary system earth current using the earth fault CT input e.g. CT4.
The switch onto fault elements are automatically enabled during the Manual Close Pulse and the
Manual Close Reclaim time and disabled at any other time unless the Line Check input is energized.
The Line Check input provides an additional alternative method to apply the switch onto fault function. The
50SOTF elements provide additional 3 phase overcurrent and measured earth fault elements that can be set to
suit fault detection during energization of a circuit. Typically these elements are set faster than graded over-
current and earth fault protection to clear faults when the circuit-breaker is closed onto a faulted system.
Each element can be selected to operate using RMS or fundamental frequency measurement.
Blocking of the Stage
The 50SOTF function can be disabled if it is not required.
Each element can be individually enabled.
Each element has an inhibit input that can be operated by binary input, comms protocols or user logic. When
an element inhibit is applied, a picked-up protection element will reset.
If an element is picked up or even operated at the end of the Manual Close Reclaim time the element will
be reset and disabled.
Each element can be set to be inhibited by inrush current detected by the 81HB2 element. Phase overcurrent
elements are inhibited by 2
nd
harmonic content on the affected phase. Earth fault elements are inhibited by
2
nd
harmonic content on any phase.
5.16
5.16.1
5.16.2
Protection and Automation Functions
5.16 50SOTF Switch onto Fault
Reyrolle 7SR5, Overcurrent Protection Device, Device Manual 241
C53000-G7040-C014-1, Edition 11.2019