GE 845 Instruction Manual page 217

CHAPTER 4: SETPOINTS
FASTPATH:
FASTPATH:
845 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
Path:
Setpoints > System > Transformer > Xfmr Status Detection
..\Transformer\Xfmr Status Detection
Item Name
Sensing by Breakers Open
All Breakers Open
Sensing by Voltage
Minimum Voltage
Current Supervision
Minimum Current
XfmrStat
SENSING BY BREAKERS OPEN
Range: Disabled, Enabled
Default: Disabled
This method of sensing indicates that when all transformer breakers are detected open,
the transformer must be de-energized. For a more secure detection, the breakers open
detection can be supervised by the detection of the minimum current, when the Current
Supervision setpoint is enabled.
ALL BREAKERS OPEN
Range: Off, Any FlexLogic Operand
Default: Off
Select the FlexLogic operand from the list representing to assert a flag when all
transformer breakers are open. This can be "52b" contacts from the transformer
breakers wired in series before connected to the relay, or another FlexLogic operand
(Virtual Output) becoming high upon the open status of all breakers.
SENSING BY VOLTAGE
Range: Disabled, Enabled
Default: Disabled
Select "Enabled", to detect the transformer status by measuring voltage.
In order for the relay to detect the transformer status accurately, the VTs must be placed
within the differential zone of protection between the Breaker and the winding. If the VTs
are placed outside the zone of protection, the transformer status will not be correct. Even
when the breaker is open, the relay can show the Transformer Energized status.
MINIMUM VOLTAGE
Range: 0.50 to 0.99 x VT in steps of 0.01 x VT
Default: 0.85 x VT
Select the minimum voltage level required for the energized/de-energized transformer
status.
During faults the voltage tends to decrease. If the voltage stays below the minimum
voltage for more than 50 ms, the transformer will show the transformer de-energized
status. This situation can be avoided if Current Supervision is set to "Enabled". In this case,
even if all the voltages collapse below the minimum voltage level, the transformer will still
show energized, because during fault conditions at least one phase will measure
substantial current.
Value Unit
Disabled
Off
Disabled
0.85 x VT
Disabled
0.050 x CT
SYSTEM
4–113