Sel SEL-421 - Directional Element Enables; A0; Order; E32 Iv

R.1.30
SEL-421 Relay Reference Manual Date Code 20111215
Protection Functions
Ground Directional Element
Typically, you can apply the default calculations that appear in Table 1.28 for
the settings Z2F, Z2R, Z0F, and Z0R. For series-compensated lines, calculate
each of these settings separately. The forward threshold setting must be less
than corresponding reverse threshold setting to avoid the situation where the
measured apparent impedance satisfies both forward and reverse conditions.
a0
Positive-sequence current restraint factor a0 is the ratio of the magnitude of
zero-sequence current to the magnitude of positive-sequence current, |I
0
|/|I
1
|.
If the relay measures a ratio greater than a0, the zero-sequence voltage-
polarized directional element is enabled. Typically you can apply the default
calculations that appear in Table 1 .28.
ORDER
The SEL-421 uses Best Choice Ground Directional™ logic to determine the
order in which the relay selects 32QG, 32V, or 32I to provide directional
decisions for the ground distance elements and the residual ground directional
overcurrent elements. Directional element classification is as follows:
➤ Q—Negative-sequence voltage-polarized directional element
(32QG)
➤ V—Zero-sequence voltage-polarized directional element (32V)
➤ I—Zero-sequence current-polarized directional element (32I)
You can set ORDER with any combination of Q, V, and I. The listed order of
these directional elements determines the priority that these elements operate
to provide the ground directional element.
Set E32 := Y to edit the ground directional element settings. If you set
E32 := Y the relay hides certain relay settings depending on the setting
ORDER.
If ORDER does not contain Q, the relay hides the Z2F, Z2R, a2, and k2
settings. If ORDER does not contain V, the relay hides the Z0F and Z0R
settings. If ORDER contains only Q, the relay hides settings a0, E32IV, Z0F,
and Z0R.
E32IV
SELOGIC control equation setting E32IV must be asserted to enable the zero-
sequence voltage-polarized or zero-sequence current-polarized directional
elements. This provides directional control of the ground distance elements
and directional residual ground overcurrent elements.
Directional Element
Enables
The Relay Word bits shown in Table 1.29 indicate when the relay has enabled
the ground directional element.
Table 1.29 Ground Directional Element Enables
Name Description
32QE Negative-sequence voltage-polarized directional element enable—phase
faults
32QGE Negative-sequence voltage-polarized directional element enable
—ground
faults
32VE Zero-sequence voltage-polarized directional element enable
—ground faults
32IE Zero-sequence current-polarized directional element enable
—ground faults