GE L90 Instruction Manual page 457

CHAPTER 5: SETTINGS
The forward-looking function is designed to be more secure compared to the reverse-looking function, so use the forward-
looking function for the tripping direction. The reverse-looking function is faster compared to the forward-looking function,
so use the reverse-looking function for the blocking direction. This allows for better protection coordination. Take this bias
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
setting value.
 CURRENT CUT-OFF LEVEL
Settings
— Specifies the offset impedance used by this protection. The primary application for the offset
NEG SEQ DIR OC1 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 is several
times smaller. Enter the offset impedance in secondary ohms.
— Selects the operating mode for the overcurrent unit of the element. The choices are "Neg
NEG SEQ DIR OC1 TYPE
Sequence" and "Zero Sequence." In some applications it is advantageous to use a directional negative-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
or 0.125 (in "Neg Sequence" mode) for backward compatibility with revisions 3.40 and earlier. Set it to zero to remove the
restraint. Set it higher if large system unbalances or poor CT performance are expected.
— Select the element characteristic angle (ECA) for the forward direction. The element
NEG SEQ DIR OC1 FWD ECA
characteristic angle in the reverse direction is the angle set for the forward direction shifted by 180°.
NEG SEQ DIR OC1 FWD LIMIT ANGLE
direction.
NEG SEQ DIR OC1 FWD PICKUP
threshold applies to zero-sequence or negative-sequence current based on the
specifying this setting, keep in mind that the design uses a positive-sequence restraint technique.
NEG SEQ DIR OC1 REV LIMIT ANGLE
direction.
— Defines the pickup level for the overcurrent unit in the reverse direction. This pickup
NEG SEQ DIR OC1 REV PICKUP
threshold applies to zero-sequence or negative-sequence current based on the
selecting this setting, keep in mind that the design uses a positive-sequence restraint technique.
L90 LINE CURRENT DIFFERENTIAL SYSTEM – INSTRUCTION MANUAL
— Controls the positive-sequence restraint. Set it to 0.063 (in "Zero Sequence" mode)
— Defines a symmetrical limit angle (in both directions from the ECA) for the forward
— Defines the pickup level for the overcurrent unit in the forward direction. This pickup
— Defines a symmetrical limit angle (in both directions from the ECA) for the reverse
GROUPED ELEMENTS
PRODUCT SETUP  DISPLAY PROPERTIES
setting. When
NEG SEQ DIR OC1 TYPE
setting. When
NEG SEQ DIR OC1 TYPE
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