GE G30 Instruction Manual page 441

CHAPTER 5: SETTINGS
low-side system impedance is minimal when checking for this condition. A similar situation arises for a wye/delta/wye
transformer, where current in one transformer winding neutral can reverse when faults on both sides of the
transformer are considered.
• If "Dual" polarizing is selected, the element performs both directional comparisons as described. A given direction is
confirmed if either voltage or current comparators indicate so. If a conflicting (simultaneous forward and reverse)
indication occurs, the forward direction overrides the reverse direction.
• If "Dual-V" polarizing is selected, "Voltage" polarizing is performed and "Current" polarizing is ignored if the voltage
polarizing signal is valid; otherwise "Current" polarizing is performed if the current polarizing signal is valid. If neither of
them is valid, neither forward nor reverse indication is given.
• If "Dual-I" polarizing is selected, "Current" polarizing is performed and "Voltage" polarizing is ignored if the current
polarizing signal is valid; otherwise "Voltage" polarizing is performed if the voltage polarizing signal is valid. If neither of
them is valid, neither forward nor reverse indication is given.
— Selects the polarizing voltage used by the directional unit when "Voltage," "Dual," "Dual-V," or
NEUTRAL DIR OC1 POL VOLT
"Dual-I" polarizing mode is set. The polarizing voltage can be programmed to be either the zero-sequence voltage
calculated from the phase voltages ("Calculated V0") or supplied externally as an auxiliary voltage ("Measured VX").
— This setting indicates whether the 3I_0 current calculated from the phase currents, or the
NEUTRAL DIR OC1 OP CURR
ground current is used by this protection. This setting acts as a switch between the neutral and ground modes of operation
(ANSI devices 67N and 67G). If set to "Calculated 3I0," the element uses the phase currents and applies the positive-
sequence restraint. If set to "Measured IG," the element uses ground current supplied to the ground CT of the CT bank
configured as
NEUTRAL DIR OC1 SOURCE
be "Voltage", as it is not possible to use the ground current as an operating and polarizing signal simultaneously. IG current
has to be above 0.05 ps to be used as operate quantity.
NEUTRAL DIR OC1 POS-SEQ RESTRAINT
for backward compatibility with firmware revision 3.40 and older. Set it to zero to remove the restraint. Set it higher if large
system unbalances or poor CT performance are expected.
— This setting specifies the offset impedance used by this protection. The primary application for
NEUTRAL DIR OC1 OFFSET
the offset impedance is to guarantee correct identification of fault direction on series compensated lines. 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 is not to be larger than the zero-sequence impedance of the protected
circuit. Practically, it shall be several times smaller. Enter the offset impedance in secondary ohms.
— This setting defines the characteristic angle (ECA) for the forward direction in the "Voltage"
NEUTRAL DIR OC1 FWD ECA
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
forward direction.
NEUTRAL DIR OC1 FWD PICKUP
direction. When selecting this setting, keep in mind that the design uses a positive-sequence restraint technique for the
"Calculated 3I0" mode of operation.
NEUTRAL DIR OC1 REV LIMIT ANGLE
reverse direction.
— This setting defines the pickup level for the overcurrent unit of the element in the reverse
NEUTRAL DIR OC1 REV PICKUP
direction. When selecting this setting, keep in mind that the design uses a positive-sequence restraint technique for the
"Calculated 3I0" mode of operation.
Proper application of this element requires that the operating current and the polarizing voltage (or current) be
measured from the same side of the transformer.
G30 GENERATOR PROTECTION SYSTEM – INSTRUCTION MANUAL
. If this setting is "Measured IG," then the
— This setting controls the amount of the positive-sequence restraint. Set it to 0.063
— This setting defines a symmetrical (in both directions from the ECA) limit angle for the
— This setting defines the pickup level for the overcurrent unit of the element in the forward
— This setting defines a symmetrical (in both directions from the ECA) limit angle for the
GROUPED ELEMENTS
NEUTRAL DIR OC1 POLARIZING
setting must
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