GE L90 Instruction Manual page 733

CHAPTER 10: THEORY OF OPERATION
For CA/CAG faults:
For ABC faults:
where
V and I are the composite voltage and composite current
COMP COMP
I0M = IG/3 and IG is the ground current of the adjacent parallel line
The two terminal equations are similar, and only need replace the subscript of (X) and (TAP) with (LOC) and (REM).
10.6.2.3 Example
Consider a three-terminal, 500 kV application with no charging current compensation or zero-sequence removal. The
phase rotation is ABC and the following CT and VT data is known.
Table 10-37: CT and VT application data for multi-ended example (assumes 87L and fault locator sources are identi-
cal)
Value Relay 1
CT primary 1200 A
CT secondary 5 A
VT connection wye
VT secondary 57.73 V
VT ratio 5000:1
The following table shows the tap settings.
Table 10-38: Tap settings for multi-ended example
Value
CT tap 1 for remote terminal 1
CT tap 1 for remote terminal 2
The following table shows the primary positive-sequence impedances and length for the line.
Table 10-39: Line length and positive sequence impedance for multi-ended example
Value Relay 1 to tap
Impedance 21.29 Ω ∠80.5°
Length 70 km
The figure shows how the three relays are connected.
L90 LINE CURRENT DIFFERENTIAL SYSTEM – INSTRUCTION MANUAL
Relay 2 Relay 3
1000 A 1600 A
1 A 5 A
delta wye
83.33 V 57.73 V
6000:1 5000:1
Relay 1 Relay 2
1000 / 1200 = 0.8333 1200 / 1000 = 1.200
1600 / 1200 = 1.3333 1600 / 1000 = 1.600
Relay 2 to tap Relay 3 to tap
36.50 Ω ∠80.5° 16.73 Ω ∠80.5°
120 km 55 km
FAULT LOCATOR
Relay 3
1200 / 1600 = 0.750
1000 / 1600 = 0.625
Eq. 10-69
Eq. 10-70
Eq. 10-71
Eq. 10-72
10
10-55