Areva MiCOM P125, Technical Manual

Page: 258 / 362

P12y/EN AP/D32 Application Guide
Page 60/74 MiCOM P125/P126 & P127
5.13 Switch onto Fault Protection & Trip on Reclose (SOTF/TOR) (P126 & P127)
5.13.1 General
It can happen, in particular plan conditions that when the feeder is supplied by the closing of
the CB a fast tripping may be required if a fault is present. (Closing on to fault)
Some faults may be due to conditions not removed from the feeder after a reclosing cycle or
manual tripping, or due to earthing clamps left on following maintenance works. In these
cases, it may be desirable to clear the fault condition in fast time, rather than waiting for the
trip delay time DMT or IDMT associated with the involved protection.
In the case of manually closing of the CB it can happen to switch on to an existing fault. This
is a particularly critical situation, because the overcurrent protection would not clear the fault
until the set operate delay had elapsed. This is another typical case of closing on to fault.
Hence the fastest possible clearance of the fault is desirable.
The P126 and P127 relays provide the SOTF/TOR functionality.
The SOTF acronym means switch on to fault.
The TOR acronym means trip on recloser.
The available setting to enable/disable/set the SOTF/TOR function is written in a submenu of
the AUTOMATIC CTRL menu.
The setting regarding the I>> and I>>> is provided to initiate the Sotf function.
5.13.2 SOTF/TOR description
The SOTF/TOR function can be initiated by a local manual control close CB detected by the
digital input Man. Close, or by a TC (closing command by remote via network: Modbus, IEC
60870, DNP3, Courier) or by an automatic reclosing cycle.
When CB has closed to some faults caused by flash or something else, the detection of the
fault needs of a time period, this is the reason because a time window after initiation of the
SOTF/TOR function is included.
This time window is realised by a fixed timer with a delay time of 500ms.
When this fixed timer is elapsed and the I>> or I>>> is detected, the timer settable t Sotf
starts.
The reason of existence of this settable timer is justified because in some application
selectivity for fault occurring in stage two or three is requested.
Another justification of the using of the SOTF/TOR tripping time delay is for some cases
where serious transient happen, the three poles of the CB do not close to the same time and
in those cases where the CB may not be closed instantaneously.
Further, the t SOFT can also be considered a trip delay time that substitutes the trip timer of
the started threshold such to accelerate the tripping.
If a trip due to switch on to fault occurs during the reclaim time of the ARC, the trip will be
definitive and the ARC will be locked.
If the I>> and I>>> reset during the settable timer t Sotf the SOTF/TOR function resets.
The SOTF/TOR functionality diagram is shown below.