Negative-Sequence Current - GE F60 Instruction Manual

5 Z SETTINGS
The positive-sequence restraint must be considered when testing for pick-up accuracy and response time (multiple of
pickup). The positive-sequence restraint is removed for low currents. If the positive-sequence current is less than 0.8 pu,
then the restraint is removed by changing the constant K to zero. This results in better response to high-resistance faults
when the unbalance is very small and there is no danger of excessive CT errors, since the current is low.
The operating quantity depends on the way the test currents are injected into the F60. For single phase injection:
= ⅓ × (1 – K) × I
• I
op injected
= (1 – K) × I
• I for I_0 mode if I_1 > 0.8 pu.
op injected
The directional unit uses the negative-sequence current (I_2) and negative-sequence voltage (V_2).
The following tables define the negative-sequence directional overcurrent element.
Table 5–22: NEGATIVE-SEQUENCE DIRECTIONAL OVERCURRENT UNIT
MODE
Negative-sequence
Zero-sequence
Table 5–23: NEGATIVE-SEQUENCE DIRECTIONAL UNIT
DIRECTION
–V_2 + Z_offset × I_2
Forward
–V_2 + Z_offset × I_2
Reverse
–V_2 + Z_offset × I_2
Forward
–V_2 + Z_offset × I_2
Reverse
The negative-sequence voltage must be greater than 0.02 pu to be validated for use as a polarizing signal. If the polarizing
signal is not validated neither forward nor reverse indication is given. The following figure explains the usage of the voltage
polarized directional unit of the element.
The figure below shows the phase angle comparator characteristics for a phase A to ground fault, with settings of:
ECA = 75° (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)
GE Multilin
for I_2 mode.
OPERATING CURRENT
= |I_2| – K × I_1|
I
op
I = 3 × (|I_0| – K × |I_1|) if |I_1| > 0.8 pu
op
I = 3 × |I_0| if |I_1| ≤ 0.8 pu
op
COMPARED PHASORS
I_2 × 1∠ECA
–(I_2 × 1∠ECA)
I_2 × 1∠ECA
–(I_2 × 1∠ECA)
F60 Feeder Protection System
5.6 GROUPED ELEMENTS
5-143
5