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2.32.2 FL calculation with data at a local-terminal only
When considering the FL calculation with data at a local-terminal only, user should note the
time of this calculation is longer than the time of FL calculation with data at a local-terminal
and remote-terminals
1
. This FL calculation requires data of the reference current, which is
obtained by measuring the change in current before and after the fault occurrence. The
reference current is used to remove the influence of load voltage and arc voltage.
1
Note: In the
FL calculation with data at a local-terminal only
, more calculation time—
that are longer than three-cycles as fault continuing time—is required.
Conversely, minimum two-cycles as fault continuing time are required in the
FL
calculation with data at a local-terminal and
remote-terminals
.
If a phase-to-phase fault occurs,
Calculation principle for phase-to-phase fault
is used
with data of the reference current (Iβ"), which is obtained by measuring the change in current
before and after the fault occurrence.
If an earth fault occurs,
Calculation principle for earth fault
is used with another
reference current (Iα"), which is similarly obtained by measuring the change in the current
before and after the fault.
In order to maintain the measurement accuracy, the compensation factors for impedance
imbalance are considered in the calculation when the variation of the impedance in each phase
is large.
(i) Calculation principle for phase-to-phase fault
Equations for the calculation in the case of phase-b-to-phase-c fault
We suppose the occurrence of a phase-b-to-phase-c fault. The fault distance ( is calculated
with the following Equations (2.32-13) to (2.32-16). Equation (2.32-16) is a general expression
when lines are treated as having lumped constants; and this expression is sufficient for lines
within 100km.
where,
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