Schweitzer Engineering SEL-351P, Quick Start Manual

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4-32 Loss-of-Potential, Load Encroachment, and Directional Element Logic Date Code 990430
SEL-351P Manual Técnico
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 SECTION 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
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 SECTION 4: .9) to be enabled:
I k I
2 0
2
> ⋅
This check ensures that the relay uses the most robust analog quantities in making directional
decisions for the neutral ground and residual ground overcurrent elements.
If the internal enable:
32VE internal enable for the zero-sequence voltage-polarized, residual-current
directional element that controls the neutral ground and residual ground
overcurrent elements
is deasserted, then factor k2 is ignored as a logic enable for the 32QGE internal enable. If the
zero-sequence voltage-polarized directional elements are not 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.