Date Code 20011026 Specifications 2-5
SEL-321/321-1 Instruction Manual
Output
Load Element Asserted ZLOAD Load detected in the load-in or load-out
regions. │I
1
│ must exceed 0.1⋅I
nom
A.
Supporting Drawing: Figure 2.21.
I
nom
= Nominal rated current
NEGATIVE-SEQUENCE DIRECTIONAL CHARACTERISTICS
These characteristics supervise:
All distance operations for unbalanced faults
Directional overcurrent outputs 67N1 - 67N4 and 67Q1 - 67Q4
They can also be used to torque-control the 51N and 51Q elements. Directional elements may be
set to either default forward or deassert on loss-of-potential (LOP).
The characteristics easily accommodate strong or weak sources, long or short lines, series-
compensation, and high fault resistance.
The directional characteristics are two settable (one forward and one reverse) negative-sequence
reactance characteristics. The reaches are independently settable, and the forward and reverse
characteristics have independent negative-sequence overcurrent supervision. Thus, forward and
reverse sensitivity and selectivity are user-settable.
Both characteristics are supervised by a negative- to positive-sequence current ratio (I
2
/I
1
) check.
This supervision restrains the negative-sequence directional elements for three-phase faults with
errant I
2
. The a2 setting determines the minimum (I
2
/I
1
) ratio where directional calculations are
permitted.
Settings
Forward Reverse
Reach Z2F Z2R
3I
2
Overcurrent Supervision 50QF 50QR
│I
2
│ > a2⋅│I
1
│ Restraint Factor a2 a2
Outputs
Forward unbalanced fault 32QF
Reverse unbalanced fault 32QR
50QF or 50QR elements asserted 50Q
Supporting Drawing: Figure 2.22.
TIME-OVERCURRENT ELEMENTS (SEL-321 BASE VERSION)
Phase, negative-sequence, and residual time-overcurrent elements are available as enabled. Both
US and IEC curve shapes are supported. The phase element uses the highest measured phase
current, while the negative-sequence and residual current elements use 3I
2
and I
R
currents,
respectively.
To Next Page
Loading...
