3 BUSBAR MULTIPLE TRIPPING CRITERIA
To ensure that the tripping decision is correct, the following criteria must all be satisfied. They are enabled by
default, but can be disabled if required.
● The current differential element (I>2) indicates a fault on the protected zone.
● The check zone supervision element (I>CZ) agrees that there is a fault on the busbar.
● There was no indication of a CT circuitry failure before the fault.
● Comparing the phases of the currents involved confirms an internal fault.
The following criteria are optional to further qualify the tripping:
● An undervoltage element which is disabled by default because VT connections may not be available.
Note:
If you can’t apply undervoltage protection, we recommend that you set the minimum zone current differential
operation threshold to greater than the highest load current expected.
● Tripping criteria affected by signals mapped in the Programmable Scheme Logic, shown in the
following diagram.
Key:
External DDB Signal
V
00713
Internal function
Block BusDiff Z1
Set Z1 DifBlkMod
Set Z1 DifCbfBlk
CctFail Blk Z1
Diff Fault Z1
Idiff Start Z 1
Idiff Trip
Idiff Trip Z1
DiffTrp Z1 Blked
DiffCBFTrpZ1 Blk
In Test Mode
PhComp Blk Z 1
VT Chk Block Z1
Current differential function
8
7BB
CT circuit fail I>1
Zone current diff I>2
Check Zone current diff I>CZ
Phase Comp
VT Block
Z
1 to Z4
Z1 to Z4
Z1 to Z4
Z1 to Z4
Z1 to Z4, CZ
Z1 to Z4, CZ
Z1 to Z4, CZ
Z1 to Z4
Z1 to Z4
Z1 to Z4
Z1 to Z4
Z1 to Z4
Figure 29: Multiple tripping criteria
3.1 TRIPPING CRITERIA DDBS
The following table shows the corresponding DDB signals.
Ordinal Signal Name Use Unique ID
Description
481 Block BusDiff Z1 PFSI DDB_INHIBIT_BUSDIFF_Z1
Blocks zone 1 current differential trip
543 Set Z1 DifBlkMod PFSI DDB_SET_Z1_BLOCK_DIFF_MODE
MiCOM P747 Chapter 5 - Protection Functions
P747-TM-EN-1 103
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