4-24
Loss-of-Potential, CCVT Transient Detection,
Date Code 20010625
Load-Encroachment, and Directional Element Logic
SEL-311L Instruction Manual
Z2F and Z2R Set Automatically
If configuration setting E32 = AUTO, settings Z2F and Z2R (negative-sequence impedance
values) are calculated automatically, using the positive-sequence line impedance magnitude
setting Z1MAG as follows:
Z2F = Z1MAG/2
(
8
secondary)
Z2R = Z1MAG/2 + 0.1
(
8
secondary; 5A nominal)
Z2R = Z1MAG/2 + 0.5
(
8
secondary; 1A nominal)
50QFP—Forward Directional Negative-Sequence Current Pickup
50QRP—Reverse Directional Negative-Sequence Current Pickup
Setting Range:
0.25–5.00 A secondary (5 A nominal phase current inputs, IA, IB, IC)
0.05–1.00 A secondary (1 A nominal phase current inputs, IA, IB, IC)
The 50QFP setting (3I
2
current value) is the pickup for the forward fault detector 50QF of the
negative-sequence voltage-polarized directional elements (see Figure 4.6). Ideally, the setting is
above normal load unbalance and below the lowest expected negative-sequence current
magnitude for unbalanced forward faults.
The 50QRP setting (3I
2
current value) is the pickup for the reverse fault detector 50QR of the
negative-sequence voltage-polarized directional elements (see Figure 4.6). Ideally, the setting is
above normal load unbalance and below the lowest expected negative-sequence current
magnitude for unbalanced reverse faults.
50QFP and 50QRP Set Automatically
If configuration setting E32 = AUTO, settings 50QFP and 50QRP are set automatically at:
50QFP = 0.50 A secondary (5 A nominal phase current inputs, IA, IB, IC)
50QRP = 0.25 A secondary (5 A nominal phase current inputs, IA, IB, IC)
50QFP = 0.10 A secondary (1 A nominal phase current inputs, IA, IB, IC)
50QRP = 0.05 A secondary (1 A nominal phase current inputs, IA, IB, IC)
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.
Summary of Contents for SEL-311L
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