GE L90 Instruction Manual page 214

5.5 GROUPED ELEMENTS
• NEUTRAL DIR OC1 OP CURR: This setting indicates whether the 3I_0 current calculated from the phase currents, or
the ground current shall be used by this protection. This setting acts as a switch between the neutral and ground
modes of operation (67N and 67G). If set to "Calculated 3I0" the element uses the phase currents and applies the pos-
itive-sequence restraint; if set to "Measured IG" the element uses ground current supplied to the ground CT of the CT
bank configured as
and polarizing signal simultaneously. Therefore, "Voltage" is the only applicable selection for the polarizing mode under
the "Measured IG" selection of this setting.
• NEUTRAL DIR OC1 POS-SEQ RESTRAINT: This setting controls the amount of the positive-sequence restraint. Set
to 0.063 for backward compatibility with firmware revision 3.40 and older. Set to zero to remove the restraint. Set
higher if large system unbalances or poor CT performance are expected.
• NEUTRAL DIR OC1 OFFSET: This setting specifies the offset impedance used by this protection. The primary appli-
cation for the offset impedance is to guarantee correct identification of fault direction on series compensated lines. See
the Chapter 9 for information on how to calculate this setting. In regular applications, the offset impedance ensures
proper operation even if the zero-sequence voltage at the relaying point is very small. If this is the intent, the offset
impedance shall not be larger than the zero-sequence impedance of the protected circuit. Practically, it shall be several
times smaller. See Chapter 8 for additional details. The offset impedance shall be entered in secondary ohms.
• NEUTRAL DIR OC1 FWD ECA: This setting defines the characteristic angle (ECA) for the forward direction in the
"Voltage" polarizing mode. The "Current" polarizing mode uses a fixed ECA of 0°. The ECA in the reverse direction is
the angle set for the forward direction shifted by 180°.
• NEUTRAL DIR OC1 FWD LIMIT ANGLE: This setting defines a symmetrical (in both directions from the ECA) limit
angle for the forward direction.
• NEUTRAL DIR OC1 FWD PICKUP: This setting defines the pickup level for the overcurrent unit of the element in the
forward direction. When selecting this setting it must be kept in mind that the design uses a 'positive-sequence
5
restraint' technique for the "Calculated 3I0" mode of operation.
• NEUTRAL DIR OC1 REV LIMIT ANGLE: This setting defines a symmetrical (in both directions from the ECA) limit
angle for the reverse direction.
• NEUTRAL DIR OC1 REV PICKUP: This setting defines the pickup level for the overcurrent unit of the element in the
reverse direction. When selecting this setting it must be kept in mind that the design uses a 'positive-sequence
restraint' technique for the "Calculated 3I0" mode of operation.
5-124
. Naturally, it is not possible to use the ground current as an operating
NEUTRAL DIR OC1 SOURCE
L90 Line Differential Relay
5 SETTINGS
GE Multilin