GE L90 Instruction Manual page 322

5.6 GROUPED ELEMENTS
bias should be taken into account when using the negative-sequence directional overcurrent element to directionalize other
protection elements. The negative-sequence directional pickup must be greater than the
PROPERTIES CURRENT CUT-OFF LEVEL
• NEG SEQ DIR OC1 OFFSET: This setting specifies the offset impedance used by this protection. The primary applica-
tion for the offset impedance is to guarantee correct identification of fault direction on series compensated lines (see
the Application of settings chapter for information on how to calculate this setting). In regular applications, the offset
impedance ensures proper operation even if the negative-sequence voltage at the relaying point is very small. If this is
the intent, the offset impedance shall not be larger than the negative-sequence impedance of the protected circuit.
Practically, it shall be several times smaller. The offset impedance shall be entered in secondary ohms. See the Theory
of operation chapter for additional details.
• NEG SEQ DIR OC1 TYPE: This setting selects the operating mode for the overcurrent unit of the element. The
choices are "Neg Sequence" and "Zero Sequence". In some applications it is advantageous to use a directional nega-
tive-sequence overcurrent function instead of a directional zero-sequence overcurrent function as inter-circuit mutual
effects are minimized.
• NEG SEQ DIR OC1 POS-SEQ RESTRAINT: This setting controls the positive-sequence restraint. Set to 0.063 (in
"Zero Sequence" mode) or 0.125 (in "Neg Sequence" mode) for backward compatibility with revisions 3.40 and earlier.
Set to zero to remove the restraint. Set higher if large system unbalances or poor CT performance are expected.
• NEG SEQ DIR OC1 FWD ECA: This setting select the element characteristic angle (ECA) for the forward direction.
The element characteristic angle in the reverse direction is the angle set for the forward direction shifted by 180°.
• NEG SEQ DIR OC1 FWD LIMIT ANGLE: This setting defines a symmetrical (in both directions from the ECA) limit
angle for the forward direction.
• NEG SEQ DIR OC1 FWD PICKUP: This setting defines the pickup level for the overcurrent unit in the forward direc-
tion. Upon
NEG SEQ DIR OC1 TYPE
5
selecting this setting it must be kept in mind that the design uses a positive-sequence restraint technique.
• NEG SEQ DIR OC1 REV LIMIT ANGLE: This setting defines a symmetrical (in both directions from the ECA) limit
angle for the reverse direction.
• NEG SEQ DIR OC1 REV PICKUP: This setting defines the pickup level for the overcurrent unit in the reverse direc-
tion. Upon
NEG SEQ DIR OC1 TYPE
selecting this setting it must be kept in mind that the design uses a positive-sequence restraint technique.
SETTING
Function
Disabled = 0
Enabled = 1
SETTING
Block
Off = 0
ACTUAL VALUES
V_2
I_2
I_0
NOTE:
V_2 is negative-sequence voltage
I_2 is negative-sequence current
I_0 is zero-sequence current
SETTING
Type
= Neg Sequence
= Zero Sequence
Figure 5–101: NEGATIVE SEQUENCE DIRECTIONAL OC1 SCHEME LOGIC
5-186
setting value.
selection, this pickup threshold applies to zero- or negative-sequence current. When
selection, this pickup threshold applies to zero- or negative-sequence current. When
SETTINGS
Forward Pickup
Positive-Sequence Restraint
RUN
AND
K
( |I_0| – × |I_1| ) Pickup
RUN
AND
K
( |I_2| – × |I_1| ) Pickup
SETTINGS
Forward ECA
Forward Limit Angle
AND
Reverse Limit Angle
Offset
RUN
Voltage Polarization
SETTINGS
Reverse Pickup
Pos Seq Restraint
RUN
AND
K
( |I_2| – × |I_1| ) Pickup
RUN
AND
K
( |I_0| – × |I_1| ) Pickup
L90 Line Current Differential System
≥
OR
≥
AND
TIMER
1.25 cycles
AND
Forward
Reverse
AND
≥
OR
≥
5 SETTINGS
PRODUCT SETUP DISPLAY
FLEXLOGIC OPERAND
NEG SEQ DIR OC1 FWD
AND
1.5 cycles
FLEXLOGIC OPERAND
NEG SEQ DIR OC1 REV
827091A5.CDR
GE Multilin