Schweitzer Engineering Laboratories SEL-311C - Page 154

4.26
SEL-311C Relay Instruction Manual Date Code 20060320
Loss-of-Potential, CCVT Transient Detection, Load-Encroachment, and Directional Element Logic
Directional Control Settings
50GFP and 50GRP Set Automatically
If configuration setting E32 = AUTO, settings 50GFP and 50GRP are set
automatically at:
50GFP = 0.50 A secondary (5 A nominal phase current inputs, IA, IB, IC)
50GRP = 0.25 A secondary (5 A nominal phase current inputs, IA, IB, IC)
50GFP = 0.10 A secondary (1 A nominal phase current inputs, IA, IB, IC)
50GRP = 0.05 A secondary (1 A nominal phase current inputs, IA, IB, IC)
a0—Positive-Sequence Current Restraint Factor, |I
0
|/|I
1
|
Setting Range:
0.02–0.50 (unitless)
If preceding setting ORDER does not contain V or I (no zero-sequence
voltage-polarized or channel IP current-polarized directional elements are
enabled), then setting a0 is not made or displayed.
Refer to Figure 4.7.
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 (|I
0
| > 0.1 • |I
1
|).
Z0F—Forward Directional Z0 Threshold
Z0R—Reverse 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 settings Z0F and Z0R are not
made or displayed.
Z0F and Z0R are used to calculate the Forward and Reverse Thresholds,
respectively, for the zero-sequence voltage-polarized directional elements (see
Figure 4.10).