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Distance calculation for earth fault (in the case of A-phase earth fault)
x
=
⋅
α ⋅
1
α
{I
(R
I
I
" + R
m
1
where,
V a = fault voltage
I α = fault current = (2I a − I b − I c )/3
I α " = change of fault current before and after fault occurrence
2I a
=
I a , I b , I c = fault current
I La , I Lb , I Lc = load current
I 0s = zero sequence current
R 1 = resistance component of line positive sequence impedance
X 1 = reactance component of line positive sequence impedance
R 0 = resistance component of line zero sequence impedance
X 0 = reactance component of line zero sequence impedance
K a = impedance imbalance compensation factor
I m ( ) = imaginary part in parentheses
R e ( ) = real part in parentheses
L = line length (km)
Equations (1) and (2) are general expressions when lines are treated as having lumped constants
and these expressions are sufficient for lines within 100 km. For lines exceeding 100 km,
influences of the distributed capacitance must be considered. For this fault locator, the following
equation is used irrespective of line length to find the compensated distance x
distance x
which was obtained in equation (1) or (2).
1
−
x
= x
2
1
where,
k = propagation constant of the protected line = 0.001km
3.5.3
Starting Calculation
Calculation of the fault location is initiated by tripping signals.
3.5.4
Displaying Location
The measurement result is stored in the "Fault record" and displayed on the LCD of the relay front
panel or on the local or remote PC. For displaying on the LCD, see Section 4.2.3.1.
⋅
×
I
(V
I
α
")
L
m
a
⋅
⋅
⋅
α ⋅
α
I
I
") + R
(X
I
0
0S
e
1
−
−
−
I b
I c
2I La
I Lb
−
3
3
3
x
1
⋅
2
k
(3)
3
⎯
142
⋅
⋅
×
α
α
I
" + X
I
I
")}
K
0
0S
a
−
I Lc
⎯
6 F 2 S 0 8 4 2
(2)
with respect to
2
-1
(fixed)
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