Toshiba GRL150-100 Series Instruction Manual page 20

DIFI1 setting and Full-scale
GRL150 transmits current data to the remote terminal after the CT matching. The current data is
normalized by the DIFI1 setting value. Therfore, the full-scale of the current data is expressed by
the following equation depending on the DIFI1 setting.
= DIFI1 × 32 (A)
I
FS
where, I : Full-scale of current data
FS
When setting DIFI1, it must be ensured that I
Setting of DIFI1
The setting of DIFI1 is determined considering the minimum internal fault current for which the
relay should operate and the maximum erroneous differential current (mainly the internal charging
current) during normal service conditions for which the relay should not operate.
DIFI1 should therefore be set to satisfy the following equation:
K⋅Ic < DIFI1 < I f / K
where,
K: Setting margin (K = 1.2 to 1.5)
Ic: Internal charging current
I f : Minimum internal fault current
Setting of DIFI2
The setting of DIFI2 is determined from the following three criteria:
• Maximum erroneous current generated by CT saturation in case of an external fault
• Maximum load current
• Maximum outflow current in case of an internal fault
In the case of the first criterion, DIFI2 should be set as small as possible so that unwanted
operation is not caused by the maximum erroneous current generated by CT saturation during
heavy through current for an external fault. It is recommended normally to set DIFI2 to 2×In (In:
secondary rated current) for this criterion.
For the second criterion, DIFI2 should be set large enough such that it does not encroach on load
current.
For the third criterion, the maximum outflow current must be considered. DIFI2 should be set
larger than the largest possible value of outflow current in the case of an internal fault.
In two terminal network, the maximum outflow current is the maximum load current.
Setting of DIFSV
When using the differential current monitoring function, the setting of DIFSV is determined from
the maximum erroneous differential current during normal service conditions.
K⋅Ierr < DIFSV < DIFI1 / (1.5 to 2)
Ierr: maximum erroneous differential current
Setting of [SP.SYN]
One terminal must be set to "Master" and the other terminal to "Slave".
is greater than the maximum fault current.
FS
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