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GE UR Series Instruction Manual Page 181

Line differential relay.
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5 SETTINGS
validated for use as a polarizing signal. If the polarizing signal is not valid neither forward nor reverse indication is
given.
For a choice of current polarizing, it is recommended that the polarizing signal be analyzed to ensure that a known
direction is maintained irrespective of the fault location. For example, if using an autotransformer neutral current as a
polarizing source, it should be ensured that a reversal of the ground current does not occur for a high-side fault. The
low-side system impedance should be assumed minimal when checking for this condition. A similar situation arises for
a WYE/DELTA/WYE transformer, where current in one transformer winding neutral may reverse when faults on both
sides of the transformer are considered.
If "Dual" polarizing is selected, the element performs both directional comparisons as described above. A given direc-
tion 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.
NEUTRAL DIR OC1 POL VOLT:
Selects the polarizing voltage used by the directional unit when "Voltage" or "Dual" 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").
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 positive-sequence restraint; if set to "Measured IG"
the element uses ground current supplied to the ground CT of the CT bank configured as
rally, it is not possible to use the ground current as an operating 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 OFFSET:
This setting specifies the offset impedance used by this protection. The primary application 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 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 the THEORY OF OPERATION chapter for more 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 set-
ting it must be kept in mind that the design uses a "positive-sequence 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 set-
ting it must be kept in mind that the design uses a "positive-sequence restraint" technique for the "Calculated 3I0" mode of
operation.
GE Power Management
L90 Line Differential Relay
5.5 GROUPED ELEMENTS
. Natu-
NEUTRAL DIR OC1 SOURCE
5-97
5

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