GE MiCOM P747 Agile, Technical Manual

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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
V00713
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
87BB
CT circuit fail I>1
Zone current diff I>2
Check Zone current diff I>CZ
Phase Comp
VT Block
Z1 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
P747-TM-EN-1.1