GE D30 Instruction Manual page 322

5.6 GROUPED ELEMENTS
Table 5–27: QUANTITIES FOR "MEASURED IG" CONFIGURATION
POLARIZING MODE
Voltage
1
-- - VAG (
where: V_0
=
3
1
I_0 -- - IN
= =
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 element incorporates a current reversal logic: if the reverse direction is indicated for at least 1.25 of a power system
5 cycle, the prospective forward indication is delayed by 1.5 of a power system cycle. The element is designed to emulate an
electromechanical directional device. Larger operating and polarizing signals results in faster directional discrimination
bringing more security to the element operation.
The forward-looking function is designed to be more secure as compared to the reverse-looking function, and therefore,
should be used for the tripping direction. The reverse-looking function is designed to be faster as compared to the forward-
looking function and should be used for the blocking direction. This allows for better protection coordination.
The above bias should be taken into account when using the neutral directional overcurrent element to directionalize other
protection elements.
5-186
DIRECTIONAL UNIT
DIRECTION
–V_0 + Z_offset × IG/3
Forward
–V_0 + Z_offset × IG/3
Reverse
)
VBG VCG zero sequence voltage
+ + =
1
-- - IA ( IB IC ) zero sequence current
+ + =
3
is set to "Measured VX", one-third of this voltage is used in place of V_0. The following
D30 Line Distance Protection System
COMPARED PHASORS
IG × 1∠ECA
–IG × 1∠ECA
,
,
5 SETTINGS
OVERCURRENT UNIT
I = |IG|
op
GE Multilin