GE 750 Instruction Manual page 158

750/760
Feeder Management Relay
NEG SEQUENCE
DIRECTIONAL
5–62
d) Negative Sequence Directional Overcurrent
PATH: SETPOINTS S5 PROTECTION
[ ] NEG SEQ DIRECTIONAL
FUNCTION: Disabled
NEG SEQ DIRECTIONAL
MESSAGE
RELAYS (3-7): -----
NEG SEQ DIRECTIONAL
MESSAGE
MTA: 315° Lead
MIN POLARIZING
MESSAGE
VOLTAGE: 0.05 x VT
The negative sequence directional feature controls the operation of all negative
sequence overcurrent elements and allows them to discriminate between forward or
reverse faults. Refer to Phase Directional Overcurrent on page 5–40 for more details
on directional principles. The operating current and polarizing voltage is shown in
the following table. If the polarizing voltage drops below the
value, the direction defaults to forward.
Table 5–15: Negative Sequence Directional Characteristics
Quantity
Negative Sequence
(ABC phase sequence)
Negative Sequence
(ACB phase sequence)
The setpoints for Negative Sequence Directional are described below.
• NEG SEQ DIRECTIONAL MTA: Enter the maximum torque angle by which the
operating current leads the polarizing voltage. This is the angle of maximum
sensitivity.
• MIN POLARIZING VOLTAGE: As the system negative sequence voltage is
used as the polarizing voltage for this element, a minimum level of voltage must
be selected to prevent operation caused by system unbalanced voltages or VT
ratio errors. For well-balanced systems and 1% accuracy VTs, this setpoint can
be as low as 2% of VT nominal voltage. For systems with high-resistance
grounding or floating neutrals, this setpoint can be as high as 20%. The default
value of "0.05 x VT" is appropriate for most solidly grounded systems.
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NEGATIVE SEQUENCE
Range: Disabled,
Alarm, Control
Range: Any combination of 3 to 7
Auxiliary relays
Range: 0 to 359° Lead in steps of 1
Range: 0.00 to 1.25 x VT in steps of
0.01
Operating Current
2
I a I aI
+ +
a b c
I V
= --------------------------------------- –
a2
3
2
I aI a I
+ +
a b c
I V
= --------------------------------------- –
a2
3
S5 Protection
NEG SEQUENCE DIR...
Alarm, Latched
MIN OPERATING VOLTAGE
Polarizing Voltage
2
V a V aV
+ +
a b c
= – ------------------------------------------- -
a2
3
2
V aV a V
+ +
a b c
= – ------------------------------------------- -
a2
3
GE Multilin