GE P741, Technical Manual

Page: 131 / 560

Operation P74x/EN OP/Na7
MiCOM P741, P742, P743 (OP) 5-
15
OP
The 87BB trip order can be blocked in the PU using 2 logic inputs, one to block the phase
element, the second to block the SEF element:
•
INP Block 87BB/P
•
INP Block 87BB/N
If some PUs are connected to Voltage device and not the other ones, some PU can trip
whereas the other ones are blocked by the voltage criteria coming from the Voltage device.
1.2.8.4 Busbar Protection Tripping Time delays
1.2.8.4.1 Busbar Protection Tripping Time delay in the CU
In the CU, the 87BB tripping time can be delayed by a settable time, the fault has to be
detected by the phase element only.
That allows, for example the clearance of the fault by a fuse on the fault feeder before
tripping the whole zone.
1.2.8.4.2 Busbar Protection Tripping Time delay in a PU
In all the PUs, the 87BB tripping time can be delayed by a settable time.
That allows, for example in Generation, a sequential tripping of all feeders connected to the
faulty zone.
1.2.8.5 Busbar Protection Tripping order PU logic
In all the PUs, there are options to block the 87BB protection trip order coming from the CU.
The logic is based either on the I>2 high set phase overcurrent function or on the IN>2 high
set neutral overcurrent function, each with the following options:
•
Phase and earth fault element (87BBP&N blocking),
•
Only the 87BB phase element (87BB/P blocking),
•
Only the 87BB SEF element (87BB/N blocking),
•
A combination of the different functions (I>2 & 87BBP&N, I>2 & 87BB/P, I>2 & 87BB/N).
The 87BB blocking function have a settable drop-off timer from 200ms to 6s by step of
100ms.
1.3 Additional protections
1.3.1 Dead Zone protection (DZ)
On a feeder, if the isolators or the breaker is open, a dead zone (or end zone) is said to exist
between the open element and the CT. The P74x peripheral units can protect this zone with
the Dead Zone protection. This is a simple time delayed overcurrent and earth fault element
which is only active when a dead zone is identified in the local topology.
1.3.2 Stub protection
When a one and half breaker scheme is protected by a P74x, the stub protection can be
done using a simple time delayed overcurrent element in each PU.
The activation of this protection has to be set in the PSL and activated when all the
associated isolators are open.
In the main setting group (usually 1), there is no overcurrent protection, in the next setting
group (usually 2) this overcurrent is enabled (on top of the same setting as in the main
setting group).
The setting group will be changed from “main” to “next” in the PSL.