Schweitzer Engineering Laboratories SEL-351 - 50 GFP - Forward Directional Residual Ground Current Pickup; 50 GRP - Reverse Directional Residual Ground Current Pickup; K2 Set Automatically

4-32 Loss-of-Potential, Load Encroachment, and Directional Element Logic Date Code 20001006
SEL-351 Instruction Manual
The k2 factor is applied to internal 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 internal enable (and following negative-sequence voltage-polarized directional element in
Figure 4.8) to be enabled:
I k I
2 0
2> ×
This check assures that the relay uses the most robust analog quantities in making directional
decisions for the neutral ground and residual ground overcurrent elements.
If both of the internal enables:
32VE internal enable for the zero-sequence voltage-polarized directional element that
controls the neutral ground and residual ground overcurrent elements
32IE internal enable for the channel IN current-polarized directional element that
controls the neutral ground and residual ground overcurrent elements
are deasserted, then factor k2 is ignored as a logic enable for the 32QGE internal enable. If neither
the zero-sequence voltage-polarized nor the channel IN current-polarized directional elements are
operable, less restrictions (i.e., factor k2) are put on the operation of the negative-sequence voltage-
polarized directional element.
k2 Set Automatically
If enable setting E32 = AUTO, setting k2 is set automatically at:
k2 = 0.2
For setting k2 = 0.2, the negative-sequence current (I
2
) magnitude has to be greater than 1/5 of the
zero-sequence current (I
0
) magnitude in order for the negative-sequence voltage-polarized
directional elements to be enabled ( I I
2 0
0 2> ×. ). Again, this presumes at least one of the
internal enables 32VE or 32IE is asserted.
50GFP – Forward Directional Residual Ground Current Pickup
50GRP – Reverse Directional Residual Ground 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)
If preceding setting ORDER does not contain V or I (no zero-sequence voltage-polarized or
channel IN current-polarized directional elements are enabled), then settings 50GFP and 50GRP
are not made or displayed.
The 50GFP setting (3I
0
current value) is the pickup for the forward fault detector 50GF of the
zero-sequence voltage-polarized and channel IN current-polarized directional elements (see
Figure 4.6). Ideally, the setting is above normal load unbalance and below the lowest expected
zero-sequence current magnitude for unbalanced forward faults.
Courtesy of NationalSwitchgear.com