GE T60 Instruction Manual page 385

5 SETTINGS
1
-- - VAG (
where: V_0 VBG
= +
3
1 1
I_0 -- - IN -- - IA (
= = +
3 3
ECA = element characteristic angle
IG = ground current
Z_offset is the offset impedance, for which magnitude is the OFFSET setting and angle is the FWD ECA
When
NEUTRAL DIR OC1 POL VOLT
figure explains the usage of the voltage polarized directional unit of the element.
The figure below shows the voltage-polarized phase angle comparator characteristics for a phase A to ground fault, with:
• ECA = 90° (element characteristic angle = centerline of operating characteristic)
• FWD LA = 80° (forward limit angle = the ± angular limit with the ECA for operation)
• REV LA = 80° (reverse limit angle = the ± angular limit with the ECA for operation)
The above bias should be taken into account when using the neutral directional overcurrent element to directionalize other
protection elements.
REV Operating
Region
–ECA line
–3I_0 line
VCG
Figure 5–112: NEUTRAL DIRECTIONAL VOLTAGE-POLARIZED CHARACTERISTICS
• NEUTRAL DIR OC1 POLARIZING: This setting selects the polarizing mode for the directional unit.
– If "Voltage" polarizing is selected, the element uses the zero-sequence voltage angle for polarization. The user
can use either the zero-sequence voltage V_0 calculated from the phase voltages, or the zero-sequence voltage
supplied externally as the auxiliary voltage V_X, both from the
The calculated V_0 can be used as polarizing voltage only if the voltage transformers are connected in Wye. The
auxiliary voltage can be used as the polarizing voltage provided

AUXILIARY VT CONNECTION
source (such as broken delta connected secondary of VTs).
GE Multilin
)
VCG zero sequence voltage
+ =
IB IC ) zero sequence current
+ =
is set to "Measured VX", one-third of this voltage is used in place of V_0. The following
REV LA
–3V_0 line
line
VAG
(reference)
LA
LA
REV LA
3V_0 line
line
is set to "Vn" and the auxiliary voltage is connected to a zero-sequence voltage
T60 Transformer Protection System
5.6 GROUPED ELEMENTS
,
,
FWD LA
line
FWD Operating
Region
LA
3I_0 line
ECA
ECA line
LA
VBG
FWD LA
line
827805A1.CDR
NEUTRAL DIR OC1 SOURCE

SYSTEM SETUP AC INPUTS
5
.

VOLTAGE BANK
5-239