4-26
Loss-of-Potential, CCVT Transient Detection,
Date Code 20011205
Load-Encroachment, and Directional Element Logic
SEL-311A Instruction Manual
The a0 factor increases the security of the zero-sequence voltage-polarized and channel IP
current-polarized directional elements. It keeps the elements from operating for zero-sequence
current (system unbalance), which circulates due to line asymmetries, CT saturation during three-
phase faults, etc.
a0 Set Automatically
If configuration setting E32 = AUTO, setting a0 is set automatically at:
a0 = 0.1
For setting a0 = 0.1, the zero-sequence current (I
0
) magnitude has to be greater than 1/10 of the
positive-sequence current (I
1
) magnitude in order for the zero-sequence voltage-polarized and
channel IP current-polarized directional elements to be enabled (
1
0
1
.
0
I
I
·
>
).
Z0F—Forward Directional Z0 Threshold
Setting Range:
-64.00 to 64.00
Ω
secondary (5 A nominal phase current inputs, IA, IB, IC)
-320.00 to 320.00
Ω
secondary (1 A nominal phase current inputs, IA, IB, IC)
If preceding setting ORDER does not contain V (no zero-sequence voltage-polarized directional
element is enabled), then setting Z0F is not made or displayed.
Z0F is used to calculate the Forward Threshold for the zero-sequence voltage-polarized
directional elements (see Figure 4.10).
If configuration setting E32 = Y, settings Z0F (zero-sequence impedance) is calculated by the
user and entered by the user.
Z0F Set Automatically
If configuration setting E32 = AUTO, setting Z0F (zero-sequence impedance) is calculated
automatically, using the zero-sequence line impedance magnitude setting Z0MAG as follows:
Z0F = Z0MAG/2
(
W
secondary)
E32IV—SEL
OGIC
Control Equation Enable
Refer to Figure 4.7.
SEL
OGIC
control equation setting E32IV must be asserted to logical 1 to enable the zero-
sequence voltage-polarized and channel IP current-polarized directional elements for directional
control of ground distance and residual ground overcurrent elements.
Most often, this setting is set directly to logical 1:
E32IV = 1
(numeral 1)
Summary of Contents for SEL-311A
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