Date Code 20001006 Loss-of-Potential, Load Encroachment, and Directional Element Logic 4-31
SEL-351 Instruction Manual
50QFP and 50QRP Set Automatically
If enable 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 4.5.
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 enable 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 ( I I
2 1
01> ×. ).
k2 – Zero-Sequence Current Restraint Factor, I
2
/I
0
Setting Range:
0.10 - 1.20 (unitless)
Note the internal enable logic outputs in Figure 4.5:
32QE internal enable for the negative-sequence voltage-polarized directional element that
controls the negative-sequence and phase overcurrent elements
32QGE internal enable for the negative-sequence voltage-polarized directional element that
controls the neutral ground and residual ground overcurrent elements
Courtesy of NationalSwitchgear.com
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