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2.6.4 Stub protected by DIFL (Stub-DIFL)
Figure 2.6-10 depicts that a one-and-a-half CB arrangement (1.5CBs) with a single
transmission line having a disconnector (DS). A ‘stub zone’ is defined within two CBs and a DS,
which is hatched in the figure.
Figure 2.6-10 Fault occurred beyond Stub zone
(i) DIFL operation at terminal-G
As the Figure 2.6-10 is illustrated, the IED_G and the IED_H are used to protect the line GH.
We suppose that a fault occurs beyond the local DS. If a countermeasure is absent from the
DIFL function, a trip signal for CBs may be issued in spite of the line GH being taken out of
service. Thus, the DIFL function is required to have the countermeasure when the fault occurs
beyond the local DS that is open. Issuing no trip signal is made by letting the current data
receiving from the opposite be zero. Note that the DIFL function begins to issue a three-phase
trip signal locally when the countermeasure is enabled.
Figure 2.6-11 depicts the DIFL logic for the stub protection. On should be set for scheme
switch [DIFL-STUB] if the user wishes not to operate the DIFL function when a fault occurs
beyond the local DS; the current data receiving from the opposite terminal is set to be zero
while the DS is open. Incidentally the information signal (DS_OPEN), which starts to be
TRUE(1) when the DS is taken to be open, is provided by the protection common function
(PROT_COMMON), which is discussed separately.
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