GE G30 Instruction Manual page 439

CHAPTER 5: SETTINGS
Table 5-35: Quantities for "calculated 3I0" configuration
Directional unit
Polarizing mode Direction
Voltage Forward
Reverse
Current Forward
Reverse
Dual, Dual-V, Dual-I Forward
Reverse
Table 5-36: Quantities for "measured IG" configuration
Directional unit
Polarizing mode Direction
Voltage Forward
Reverse
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
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.
G30 GENERATOR 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
5-225
5