Toshiba GR-200 Series Instruction Manual page 272

Application guidelines
2.22.8
The application of settings in the ARC function requires careful consideration of the following
factors:
Frequency and nature of faults
The frequency and nature of faults on the distribution line help to decide upon the number of
ARC shots desired.
If the majority of the faults are transient, (e.g. due to lightning), then applying a single-
shot scheme would be appropriate.
If a significant percentage of faults on the distribution line are semi-permanent (e.g. due
to foreign objects like a small tree branch or small animal that may have fallen across the line),
then adopting a multi-shot scheme becomes advantageous.
If transient or semi-permanent faults are rare (e.g. overhead distribution line in urban
areas or a feeder that has a significant portion of cable), then non-use of the ARC function will
be appropriate.
CB characteristics
The capability of a CB for ARC duty must be checked. The CB characteristics such as the
number of successive open-close (OC) duty cycles and the dead time required between an open-
close operation will determine the number of ARC shots employed and the minimum dead time
before an ARC shot can be given.
De-ionization time
The time taken for de-ionization of the fault arc path is an important consideration for
determining the dead time before an ARC shot can be given. The de-ionization period depends
upon the system voltage, the fault current and the duration of the fault. Capacitive coupling
between the unfaulted phase and the faulted phase will increase the de-ionizing time; however,
this is not applicable for a relay for distribution systems, because tripping is always three-
phase. A de-ionization time of at least 100ms may be considered for distribution voltages (66KV
and below).
System stability
The intrinsic stability of an interconnected power system will determine the maximum dead
time allowable before the ARC shot must be issued. This may not apply to conventional
distribution systems where the generating source is remote from the load centers. However,
with distributed generation located closer to load centers, stability becomes an important
consideration. Transient stability studies can establish the maximum dead time allowed for
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6F2T0200 (0.15)
GRE200 (1,2)