83
6
F
2
S
0
8
5
0
2.5 Overcurrent Backup Protection
Inverse time and definite time overcurrent protections are provided for phase faults and earth
faults respectively.
Scheme logic
The scheme logic of the overcurrent backup protection is shown in Figures 2.5.1 and 2.5.2. The
overcurrent protection issues single-phase tripping signals in the operation of OC and OCI, and
issues a three-phase tripping signal BU-TRIP in the operation of EF or EFI element. Three-phase
tripping of OC and OCI is available by PLC signals OC_3PTP and OCI_3PTP. Tripping by each
element can be disabled by the scheme switches [OCBT], [OCIBT], [EFBT] and [EFIBT]. The
EF element issues an alarm for the backup trip for earth fault. The alarm can be disabled by the
scheme switch [EFBTAL].
The overcurrent backup protection can be blocked by the binary input signal BUT_BLOCK.
Tripping by each protection can be blocked by PLC signals OC_BLOCK, OCI_BLOCK,
EF_BLOCK and EFI_BLOCK. The OC and EF can trip instantaneously by PLC signals
OC_INST_TP and EF_INST_TP.
The OC and OCI protections can connect to the Fail-safe elements by PLC. Then the outputs of
Fail-safe elements are connected to OC-A_FS, OC-B_FS, OC-C_FS, OCI-A_FS, OCI-B_FS
and OCI-C_FS.
OC_INST_TP
1633
+
&
0.00 – 10.00s
TOC
OC-A
t
0
t
0
t
0
"ON"
[OCBT]
&
1
OC_BLOCK
1589
1
BUT_BLOCK
1550
65
66
67
&
&
&
≥
1
113
OC_TRIP
OC-A TP
OC-B TP
OC-C TP
≥
1
≥
1
≥
1
OC_3PTP
1650
461
460
459
OC-A TRIP
OC-B TRIP
OC-C TRIP
OC-B
OC-C
[OCIBT]
&
"ON"
+
&
OCI_BLOCK
1590
1
68
69
70
≥
1
114
OCI_TRIP
OCI-A TP
OCI-B TP
OCI-C TP
1651 OCI_3PTP
464
463
462
OCI-A TRIP
OCI-B TRIP
OCI-C TRIP
OCI-A
OCI-B
OCI-C
&
&
&
&
&
&
≥
1
≥
1
≥
1
OCI-C_FS
1742
OCI-B_FS
1741
OCI-A_FS
1740
OC-C_FS
1738
OC-B_FS
1737
≥
1
≥
1
≥
1
OC-A_FS
1736
Figure 2.5.1 Overcurrent Backup Protection OC and OCI
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