Switch-Onto-Fault Protection - Toshiba GRL100-701B Instruction Manual

2.12 Switch-Onto-Fault Protection

The current differential protection can trip against a switch-onto-fault. However, the distance
protection cannot operate against a switch-onto-fault. Therefore, the switch-onto-fault
protection should be applied when the current differential protection is out of service.
In order to quickly remove a fault which may occur when a faulted line or busbar is energized,
the switch-onto-fault (SOTF) protection functions for a certain period after the circuit breaker is
closed.
The SOTF protection is performed by a non-directional overcurrent element and distance
measuring elements. The overcurrent protection is effective in detecting close-up three-phase
faults on the line in particular when the voltage transformer is installed on the line side. This is
because the voltage input to the distance measuring elements is absent continuously before and
after the fault, and thus it is difficult for the distance measuring elements to detect the fault.
The distance measuring elements can operate for faults other than close-up three-phase faults.
One of the zone 1 to zone R elements can be used for the SOTF protection.
Scheme logic
The scheme logic for the SOTF protection is shown in Figure 2.12.1. The SOTF protection
issues a three-phase tripping signal M-TRIP for the operation of an overcurrent element OCH or
distance measuring elements Z1 to ZＲ for 500 ms after the circuit breaker is closed (CB-OR =
1) and/or for 500ms after the undervoltage dead line detector resets. The method of controlling
the SOTF protection by CB closing and/or by undervoltage dead line detection is selected by
scheme switch [SOTF-DL]. Elements UVFS and UVLG provide undervoltage dead line
detection.
Tripping by each element can be disabled by the scheme switches [SOTF-OC] to [SOTF-R].
When a VT failure is detected (NON VTF = 0), tripping by the distance measuring elements is
blocked.
622 UVLS-AB
623 UVLS-BC
624 UVLS-CA
UVLS
628 UVLG-A
629 UVLG-B
630 UVLG-C
UVLG
CB-OR
599 OCH-A
600 OCH-B
601 OCH-C
OCH
[SOTF-Z1]
Z1
[SOTF-Z2]
Z2
[SOTF-Z3]
Z3
[SOTF-R]
ZR
SOTF_BLOCK
1901
[SOTF-DL]
TSOTF
t
&
"UV",
"Both"
0 - 300s
TSOTF
t
1
"CB",
0 - 300s
"Both"
[SOTF-OC]
"ON"
"ON"
"ON"
≥1
"ON"
"ON"
1
Figure 2.12.1
 107 
0
0 t
0
≥1
&
0.5s
NON VTF
SOTF Scheme Logic
6 F 2 S 0 8 5 0
&
816
SOTF-TRIP
≥1
&