Date Code 20011112
Line Current Differential, Distance, Out-of-Step, Overcurrent,
3-35
Voltage, Synchronism Check, and Frequency Elements
SEL-311L Instruction Manual
V
B
V
AB
- rZ
• I
AB
Unfaulted
V
A
V
C
Test Angle
sin (
θ
< 180
°
) > 0
V
C
mem
-j •
V
AB
- 0
.25
• V
C
m
em
V
AB
- rZ
• I
AB
-j •
V
AB
- 0
.25
• V
C
m
em
Test Angle
sin (
θ
< 180
°
) > 0
V
A
V
B
V
C
V
AB
- rZ
• I
AB
-j •
V
AB
- 0
.25
• V
C
m
em
Test Angle
sin (
θ
> 180
°
) < 0
V
A
V
B
V
C
V
C
mem
External Fault
Internal Fault
Note: V
A
, V
B
, and V
C
are internal element voltages, not system voltages.
V
C
mem
M311L115
Figure 3.28: Compensator-Distance Three-Phase Element Operation
Positive-sequence polarized and compensator distance mho elements each have different
operating advantages in different protection environments, but work equally well in the majority
of transmission line applications. Consider using compensator distance elements when:
•
A different phase-distance operating principle is desired for backup relaying.
•
Protecting a transmission line through a delta-wye transformer. The compensator
distance element reaches through a delta-wye transformer bank for phase-to-phase,
phase-to-phase-to-ground, and three-phase faults. Calculate the total primary
impedance as the sum of the per-unit transformer and line impedances, then convert
from per-unit to actual primary impedance at the protected bus voltage. The
Summary of Contents for SEL-311L
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