Schweitzer Engineering Laboratories SEL-321 - Phase Voltage Elements; Positive-Sequence Overvoltage Elements; Zero-Sequence Overvoltage Element

2-8 Specifications Date Code 20011026
SEL-321/321-1 Instruction Manual
Phase Voltage Elements
Single-phase and three-phase elements compare individual voltage magnitudes against under-
and overvoltage thresholds.
Zero-Sequence Overvoltage Element
The zero-sequence overvoltage element (59N) is used in the Weak-Infeed logic of the
Permissive-Overreaching Transfer Trip Scheme logic. The 59N element output is also available
for use in the programmable logic.
Positive-Sequence Overvoltage Elements
There are two positive-sequence (V
1
) overvoltage elements: local bus (59PB) and remote bus
(59PR). The 59PB element measures V
1
at the local bus. The 59PR element operates on an
estimate of the voltage at the remote bus. The estimate is V
1
remote = V
1
- a1⋅Z
1
L⋅I
1
, where Z
1
L
is the positive-sequence replica line impedance, I
1
is the positive-sequence current, and a1 is a
settable scale factor.
Settings
Mag. Delay I
1
Comp.
Zero-Seq. O/V 59N
Bus Phase U/V 27L
Bus Phase O/V 59L
V
1
Local O/V 59PB 59PBD
V
1
Remote O/V 59PR 59PRD a1
Outputs
1∅ 3∅ Seq. Use in Other Logic
Zero-Seq. O/V 59N Weak-Infeed Logic
Neg.-Seq. O/V 59QL Loss-of-Potential Logic
Bus Phase U/V 27L 3P27 Weak-Infeed Logic (27L)
Bus Phase O/V 59L 3P59 No
V
1
Voltage 59PL Loss-of-Potential Logic
V
1
Local O/V 59PB (w/ 59PBD Delay) No
V
1
Remote O/V 59PR (w/ 59PRD Delay) No
Supporting Drawings: Figure 2.29 and Figure 2.30.
TIME-STEP BACKUP LOGIC TIMERS
Independent timers are provided for Zones 2, 3, and 4 of phase and ground distance protection
and for each level of residual and negative-sequence overcurrent protection.
Timer Settings
Phase 21 Gnd 21 67N 67Q
Zone/Level 1 67NL1D 67QL1D
Zone/Level 2 Z2PD Z2GD 67NL2D 67QL2D
Zone/Level 3 Z3PD Z3GD 67NL3D 67QL3D
Zone/Level 4 Z4PD Z4GD 67NL4D 67QL4D