8-4
L60 LINE PHASE COMPARISON SYSTEM – INSTRUCTION MANUAL
DISTANCE/BACKUP SUPERVISION
CHAPTER 8: APPLICATION OF SETTINGS
8
•
100 miles long
•
50 ohms primary impedance
•
5520 ohms shunt capacitance of the line
•
Maximum expected load of 2000 A
•
CT ratio of 2000/5
•
Minimum expected internal three-phase fault of 8000 A
Figure 8-1: Settings example
This renders the following settings.
1.
Mixed signal factor K = 0.2
2.
FDL pickup: I
FDL
= 1.1 × 2000 × 0.2 = 440 A or 440 / 400 = 1.1 A secondary.
The setting is 1.1 / 5 = 0.22 pu.
3.
FDH pickup: I
FDH
= 4/3 × I
FDL
+ 0.375 × I
capac
= 1.33 × 440 + 0.375 × 80 = 615.2 A or 615.2 / 400 = 1.54 A secondary;
setting is 1.76 / 5 = 0.31 pu. Where I
capac
= 765000/(
√
3 × 5520) = 80 A
4.
Stability angle:
φ
load = 2 × arcsin((2000 × 50 ×
√
3) / (2 × 765000)) = 13.0°
φ
capac = arctan(I
capac
/ I
FDH
) = arctan(80 / 615.2) = 7.4°
φ
s(deg) = 13.0°+7.4°+10° = 30.4°
Minimum recommended setting 60° (set as default) is applied.
5.
Check against requirement for trip supervision by distance relay. When minimum internal three-phase fault current is
at least twice the maximum line load current, no distance element is required to be assigned to the
FD INPUT
setting.
Otherwise, it is recommended to assign phase distance element to
FD INPUT
setting. In this example, the minimum
three-phase fault current is much more than twice the maximum line load current, so no distance element is assigned
to the
FD INPUT
setting.
8.2 Distance/backup supervision
8.2.1 Overview
As an economical approach to supply customer load, many high voltage (HV) lines have transformers tapped to the lines.
The figure shows a typical configuration.
