4-24
Loss-of-Potential, CCVT Transient Detection,
Date Code 20011205
Load-Encroachment, and Directional Element Logic
SEL-311A Instruction Manual
a2—Positive-Sequence Current Restraint Factor, I
2
/I
1
Setting Range:
0.02–0.50 (unitless)
Refer to Figure 4.6.
The a2 factor increases the security of the negative-sequence voltage-polarized directional
elements. It keeps the elements from operating for negative-sequence current (system
unbalance), which circulates due to line asymmetries, CT saturation during three-phase faults, etc.
a2 Set Automatically
If configuration setting E32 = AUTO, setting a2 is set automatically at:
a2 = 0.1
For setting a2 = 0.1, the negative-sequence current (I
2
) magnitude has to be greater than 1/10 of
the positive-sequence current (I
1
) magnitude in order for the negative-sequence voltage-polarized
directional elements to be enabled
(
)
1
2
1
.
0
I
I
·
>
.
k2—Zero-Sequence Current Restraint Factor, I
2
/I
0
Setting Range:
0.10–1.20 (unitless)
Note the directional enable logic outputs in Figure 4.6:
32QE
enable for the negative-sequence voltage-polarized directional element that
controls the phase distance elements
32QGE enable for the negative-sequence voltage-polarized directional element that
controls the ground distance and residual ground overcurrent elements
The k2 factor is applied to enable 32QGE. The negative-sequence current (I
2
) magnitude has to
be greater than the zero-sequence current (I
0
) magnitude multiplied by k2 in order for the 32QGE
enable (and following negative-sequence voltage-polarized directional element in Figure 4.9) to
be enabled:
0
2
I
k
I
·
>
This check assures that the relay uses the most robust analog quantities in making directional
decisions for the ground distance and residual ground overcurrent elements.
If both of the internal enables:
32VE
enable for the zero-sequence voltage-polarized directional element that controls
the ground distance and residual ground overcurrent elements
32IE
enable for the channel IP current-polarized directional element that controls the
ground distance and residual ground overcurrent elements
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