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Busbar G
G
ARC
Relay OC G in DT
(1)
G
Figure 2.22-15 Occurrence of fault and OC operations with ARC
†Note: Delayed trip commands following the instantaneous trip commands may be used
for realizing time coordination between the relays, sectionalizers and fuses.
Upon the occurrence of a permanent fault 'F', both relays G and R will issue a DT
following a DT
trip for their respective CBs; that is, in the first instance a reclose shot, (ARC
(1)
SHOT1) will be issued by both relays. Then, a second reclose shot (ARC SHOT2) will also be
issued by both the relays.
For the third reclose shot (ARC SHOT3), the difference between the settings of the
IDMT
characteristic for relays G and R will alter the operating times of their respective ARC
(3)
functions. Given that the pickup time in IDMT G
in IDMT R
, the third reclosing (ARC SHOT3) will be performed only by relay R, whereas relay
(3)
G neither issues a trip command nor an ARC shot. Consequently, relay G may now determine
that the operation of its ARC sequence has been successful and hence relay G will reset to
return to the beginning of its sequence 'ARC ready' (i.e. the ARC function at relay G will
commence from the first reclose shot 'ARC SHOT1'). Conversely, relay R is unable to issue a
fourth reclose shot (ARC SHOT4) because the delayed operation of IDMT R
not have sufficient time to operate for the fault. This is because, following the tripping for the
first DT G
, relay G issues the first reclose shot (ARC SHOT1), but its shot sequence is not
(1)
correct. Figure 2.22-16 illustrates how tripping and reclosing are not performed correctly; thus
erroneous coordination between the ARC operations at relay G and relay R is experienced.
Lateral branch
Fuse
Fuse
, DT
, IDMT
, IDMT
(2)
(3)
G
G
Lateral branch
- 248 -
R
ARC
Relay OC R in DT
(4)
G
R
S
Sectionalizer
is delayed in comparison to the pickup time
(3)
6F2T0207 (0.01)
Permanent Fault F
Main feeder
, DT
, IDMT
, IDMT
(1)
(2)
(3)
R
R
means that it will
(4)
GRE200 (5,6)
(4)
R
trip
(2)
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