Stub Protection - Toshiba GRL100-701B Instruction Manual

2.13 Stub Protection

In the case of a busbar with a one-and-a-half breaker arrangement as shown in Figure 2.13.1.1,
the differential protection will operate and will trip the breakers at both terminals, and the
distance protection will not operate.
GRL100-700 series provides the following two schemes of stub protection for such cases:
- STUB DIF
- STUB OC
2.13.1 STUB DIF Protection
If a fault occurs at F1 or F2 when line disconnector DS of terminal A is open as shown in Figure
2.13.1, the differential protection operates and trips the breakers at both terminals.
Figure 2.13.1.1 shows the stub fault protection logic of STUB DIF using the current differential
principle.
If the switch is set to "DIF" and the disconnector is open (DS = 0), the signal STUB ON is
generated and used to reset the receiving current data from terminal B to zero. Thus, terminal A
does not need to operate unnecessarily in response to fault F2.
Terminal B detects that terminal A is out-of-service with the out-of-service detection logic and
resets the receiving current data from terminal A to zero, and so does not operate in response to
fault F1.
The signal STUB ON brings the local tripping into three-phase final tripping.
2.13.2 STUB OC Protection
In the case of a busbar with a one-and-a-half breaker arrangement, the VT is generally installed
on the line side. If the line is separated from the busbar, the distance protection does not cover to
the "stub" area between the two CTs and line isolator. This is because the line VT cannot supply
a correct voltage for a fault in the "stub" area. For a fault in the stub area under such conditions,
fast overcurrent protection is applied.
Terminal A
× × ×
F1
DS
Figure 2.13.1 Stub Fault
DS
[STUB]
(+)
"ON"
Figure 2.13.1.1 STUB DIF Protection
 109 
Terminal B
×
F2
1
&
6 F 2 S 0 8 5 0
× ×
STUB ON