Schweitzer Engineering Laboratories SEL-321 - Phase and Ground Distance Element Setting Criteria; Zone 1 Setting; Zone 2 Setting

5-4 Applications Date Code 20011026
SEL-321/321-1 Instruction Manual
Each directional setting determines the direction for that distance zone and residual or negative-
sequence overcurrent level. For example, with DIR1 = F, the Zone 1 phase and ground distance
elements and the Level 1 residual and negative-sequence elements are set in the forward-reaching
direction.
For this application, three zones of phase and ground distance protection are required. Zone 1,
Zone 2, and Zone 4 elements are set in the forward direction. Zone 3 elements are used in the
current reversal block logic and are set in the reverse direction.
PMHOZ = 3
33
3
GMHOZ = 3
33
3
QUADZ = 3
33
3
DIR1 = F
FF
F
DIR2 = F
FF
F
DIR3 = R
RR
R
DIR4 = F
FF
F
- Other Settings Affected
Number of distance element and supervisory overcurrent settings.
Phase and Ground Distance Element Setting Criteria
Zone 1 Setting
The Zone 1 elements provide instantaneous protection for phase-to-phase, three-phase, and
phase-to-ground faults in the first 80-90% of the transmission line. The remainder of the line is
protected by the overreaching Zone 2 elements. While the percent error of the impedance
element reach is less than 5%, errors in the CT and PT ratios, modeled transmission line data,
and fault study data do not permit Zone 1 element settings of 100%.
In this example, the Zone 1 distance elements at Breaker 3 must not reach past Bus C. To
prevent overreaching due to the sources of error listed above, the required reach for the Zone 1
three-phase, phase-to-phase, and phase-to-ground mho distance elements are 80% of the
positive-sequence impedance of Line 2.
Zone 1 Reach = 0.80 ⋅ 78.03 Ω primary ∠84° = 62.42 Ω primary ∠84°
The Zone 1 quadrilateral element setting is based upon the same requirements established for the
Zone 1 mho elements. The reactive reach is set the same as the mho distance setting. The
resistive reach determines sensitivity for high resistance faults on a radial basis. For this
example, the Zone 1 resistive reach is set for 25 Ω primary.
Zone 2 Setting
The Zone 2 elements must have adequate reach to detect all phase-to-phase, three-phase and
phase-to-ground faults along Line 2, but cannot overreach the Zone 1 elements for faults on
either Line 3 or Line 6. In this example, the impedances for Lines 3 and 6 are identical.
ZL for Line 2 = 78.03 Ω primary
ZL for Line 3 = ZL for Line 6 = 39.12 Ω primary