GE T60, Instruction Manual

Page: 385 / 796

GE Multilin T60 Transformer Protection System 5-239
5 SETTINGS 5.6 GROUPED ELEMENTS
5
where: ,
,
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
is set to “Measured VX”, one-third of this voltage is used in place of V_0. The following
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.
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
NEUTRAL DIR OC1 SOURCE
.
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
SYSTEM SETUP

AC INPUTS

VOLTAGE BANK

AUXILIARY VT CONNECTION
is set to “Vn” and the auxiliary voltage is connected to a zero-sequence voltage
source (such as broken delta connected secondary of VTs).
V_0
1
3
---
VAG VBG VCG
+ +
( )
zero sequence voltage
= =
I_0
1
3
---
IN
1
3
---
IA IB IC
+ +
( )
zero sequence current
= = =
827805A1.CDR
V AG
(reference)
V BG
V CG
–3I_0 line
3I_0 line
ECA line
–ECA line
LA
LA
LA
LA
ECA
FWD LA
line
FWD Operating
Region
RE V Operating
Region
FWD LA
line
RE V LA
line
RE V LA
line
–3 V _0 line
3 V _0 line