GE L90 Instruction Manual page 501

9 THEORY OF OPERATION
For two-terminal applications, the following equalities hold for the above equation.
For two-terminal applications, the distance is reported from the local relay. In three-terminal applications, the distance is
reported from the terminal of a given line segment.
Phase rotation must be the same at all line terminals for correct operation of the multi-ended fault locator.
NOTE
b) 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 9–1: CT AND VT APPLICATION DATA FOR MULTI-ENDED EXAMPLE
VALUE RELAY 1
CT primary 1200 A
CT secondary 5 A
VT connection wye
VT secondary 57.73 V
VT ratio 5000:1
The tap settings are shown below.
Table 9–2: TAP SETTINGS MULTI-ENDED EXAMPLE
VALUE
CT tap 1 for remote terminal 1
CT tap 1 for remote terminal 2
The primary positive-sequence impedances and length for the line are shown below.
Table 9–3: LINE LENGTH AND POSITIVE-SEQUENCE IMPEDANCE FOR MULTI-ENDED EXAMPLE
VALUE
Impedance
Length
The three relays are connected as shown below.
GE Multilin
V – V
⎛
( )
1 X TAP X
--------------------------------------- -
⎜
Z
⎜
D Re ---------------------------------------------------------------- -
=
pu
⎜ I
FLT X
⎝
×
D D L
=
units pu
V = V
( )
1 X LOC X
V = V
( )
TAP X REM1 X
I I
=
( )
TAP X REM1 X
I = I +
( ) ( )
FLT X LOC X
RELAY 2
1000 A
1 A
delta
83.33 V
6000:1
RELAY 1 RELAY 2
1000 / 1200 = 0.8333 1200 / 1000 = 1.200
1600 / 1200 = 1.3333 1600 / 1000 = 1.600
RELAY 1 TO TAP RELAY 2 TO TAP
21.29 Ω ∠80.5° 36.50 Ω ∠80.5°
70 km 120 km
L90 Line Current Differential System
⎞
( )
I
+
⎟
( )
TAP X
⎟
⎟
( )
⎠
( )
( )
( )
I
( )
REM1 X
RELAY 3
1600 A
5 A
wye
57.73 V
5000:1
RELAY 3
1200 / 1600 = 0.750
1000 / 1600 = 0.625
RELAY 3 TO TAP
16.73 Ω ∠80.5°
55 km
9.4 FAULT LOCATOR
(EQ 9.49)
(EQ 9.50)
9
9-27