GE 750 Instruction Manual page 182

S5 PROTECTION
5 - 56
Table 5–11: Phase Directional Operating Characteristics
Quantity Operating
Current
Phase A Ia
Phase B Ib
Phase C Ic
To increase security for three phase faults very close to the location of the VTs used to
measure the polarizing voltage, a voltage memory feature is incorporated. This feature
remembers the last measurement of the polarizing voltage which is greater than the
value and uses it to determine direction. The voltage memory
POLARIZING VOLTAGE
remains valid for one second after the voltages have collapsed. Once the voltage memory
has expired, after one second, the phase overcurrent elements under directional control
can be set to block or trip on overcurrent. When set to "Enabled", the
setpoint will block the operation of any phase overcurrent element under
MEM EXPIRES
directional control when voltage memory expires. When set to "Disabled", directional
blocking of any Phase Overcurrent element will be inhibited. The voltage memory is
updated immediately when the polarizing voltage is restored.
To complement the voltage memory feature, a Close Into Fault (CIF) feature allows close-in
faults to be cleared when energizing a line. When the
setpoint is "Disabled", the CIF feature permits operation of any phase overcurrent element
if current appears without any voltage. When set to "Enabled" the CIF feature inhibits
operation of any phase overcurrent element under directional control under these
conditions. In both cases, directional blocking will be permitted to resume when the
polarizing voltage becomes greater than the
Setting the
BLOCK OC WHEN VOLT MEM EXPIRES
overcurrent elements under directional control (phase overcurrent element set to trip in
either the forward or reverse direction) from operating.
Settings:
• PHASE DIRECTIONAL FUNCTION: The directional element function must be selected
as "Control", "Alarm" or "Latched Alarm" to enable the directionality check to the TOC
and IOC elements as per programmed directional parameters and as described in this
section. When the "Alarm" function is selected, the 750/760 will flash the "Alarm" LED
while the direction is "REVERSE", and will turn it off when the condition disappear.
When the "Latched Alarm" function is selected, the 750/760 will flash the "Alarm" LED
while the direction is "REVERSE". In this case the "Alarm" LED will remain illuminated
after the condition has cleared, until the 750/760 RESET button is pressed.
• PHASE DIRECTIONAL RELAYS: Select auxiliary contacts (3 to 7) to enable the operation
of the output contacts (3 to 7) when the current is in REVERSE DIRECTION. If under
Output Relay Settings, the "Output Type" of the Auxiliary relays (3 to 7) is set to
"Latched", they will remain in the operated state, regardless of the status of the
"Alarm" LED, until pressing the RESET button.
polarizing voltage
ABC Phase Sequence
Vbc
Vca
Vab
BLOCK OC WHEN VOLT MEM EXPIRES
MIN POLARIZING VOLTAGE
to "Enabled" will block all phase
750 FEEDER MANAGEMENT RELAY – INSTRUCTION MANUAL
CHAPTER 5: SETPOINTS
ACB Phase Sequence
Vcb
Vac
Vba
MIN
BLOCK OC WHEN VOLT
setpoint.