- 387 -
Ib, Ic: Line-to-neutral currents when a phase-bc fault arises
Ibc: Line-to-line currents when a phase-bc fault arises (=Ib−Ic)
Vbc: Line-to-line voltages when a phase-bc fault arises (=Vb−Vc)
ILb: Load-current in phase-b before the fault
ILc: Load-current in phase-c before the fault
Iβ’: Load-current change before and after the fault (=(Ib−Ic)−(ILb−ILc))
Iβ”: Complex conjugate of Iβ’
R1: Resistance component of line impedance1 in positive-sequence
Χ1: Reactance component of line impedance1 in positive-sequence
Kbc: Compensation factor2 for imbalance impedance
L: Line length3 in the kilometer or mile
Im( ): Expression of imaginary part when a value is placed in parentheses
Re( ): Expression of real part when a value is placed in parentheses
• : Symbol of Vector product
1
Note: For example, user should set the R
1
and the X
1
with settings [FL_1R1] and
setting [FL_1X1] respectively, when the impedance of line GJ is considered in
symmetrical components, as shown in Figure 2.32-2. For further information, see
section 2.32.6(iii).
2
Note: User should set the K
ab
, K
bc
and K
ca
with settings [FL_Kab], [FL_Kbc], and
[FL_Kca], when the imbalance impedance is considered. For further information,
see section 2.32.6(vi).
3
Note: User should set the line length for settings [FL_1line_km] when the length of line
GJ is considered and when the unit of length is represented by kilometer, as
shown in Figure 2.32-2. For further information, see section 2.32.6(v).
Compensation for long line
When the line length is beyond 100km, the result of Equation (2.32-16) requires compensation.
Equation (2.32-17) is used to find the compensated distance () with respect to the fault
distance () which is the result of Equation (2.32-16):
where,
k: Propagation constant fixed of the line (
)
(ii) Calculation principle for earth fault
Equations
When we suppose the occurrence of an earth fault in phase-a, the fault distance () is
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