GE T60 Instruction Manual page 443

CHAPTER 5: SETTINGS
Table 5-39: Quantities for "calculated 3I0" configuration
Directional unit
Polarizing mode Direction
Voltage Forward
Reverse
Current Forward
Reverse
Dual, Dual-V, Dual-I Forward
Reverse
Table 5-40: Quantities for "measured IG" configuration
Directional unit
Polarizing mode Direction
Voltage Forward
Reverse
where:
ECA = element characteristic angle
IG = ground current
When
NEUTRAL DIR OC1 POL VOLT
figure explains the usage of the voltage polarized directional unit of the element.
The figure 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)
Take the bias into account when using the neutral directional overcurrent element to directionalize other protection
elements.
T60 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
Compared phasors
–V_0 + Z_offset × I_0 I_0 × 1∠ECA
–V_0 + Z_offset × I_0 –I_0 × 1∠ECA
IG I_0
IG –I_0
–V_0 + Z_offset × I_0 I_0 × 1∠ECA
or
IG I_0
–V_0 + Z_offset × I_0 –I_0 × 1∠ECA
or
IG –I_0
Compared phasors
–V_0 + Z_offset × IG/3
–V_0 + Z_offset × IG/3
is set to "Measured VX," one-third of this voltage is used in place of V_0. The following
Overcurrent unit
I = 3 × (|I_0| – K × |I_1|) if |I
op
I = 3 × (|I_0|) if |I
op
Overcurrent unit
IG × 1∠ECA I = |IG|
op
–IG × 1∠ECA
GROUPED ELEMENTS
| > 0.8 pu
1
| ≤ 0.8 pu
1
5-261
5