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Fault locator (FLOC)
case, the pre-fault and fault values of currents and voltages for a particular disturbance.
At any time a calculation of the distance to fault for a selected fault loop can be initiated
manually.
The information on distance to fault automatically appears on the local HMI for the first
fault only, if more than one fault appears within a time shorter than 10 seconds. Auto-
matic reclosing on persistent faults enables this. In such a case the first set of data is
more accurate than the second set. The unit also stores the phasors of currents and volt-
ages for the last faults. A calculation can be initiated locally or remotely.
The percentage value is also binary coded, thus the distance to fault value can also be
read on binary outputs of the terminal.
Additional information is specified in symbols before the distance-to-fault figure:
*
A non-compensated model was used for calculation
E
Error, the fault was found outside the measuring range
>
The fault is located beyond the line, in forward direction
Two signs can be combined, for example, *>
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For transmission lines with voltage sources at both line ends, the effect of double-end
infeed and additional fault resistance must be considered when calculating the distance
to the fault from the currents and voltages at one line end. If this is not done, the accu-
racy of the calculated figure will vary with the load flow and the amount of additional
fault resistance.
The calculation algorithm used in the distance-to-fault locator in REx 5xx line-protec-
tion terminals compensates for the effect of double-end infeed, additional fault resis-
tance and load current.
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Figure 180 shows a single-line diagram of a single transmission line, that is fed from
both ends with source impedances Z
tance F from terminal A on a line with the length L and impedance Z
tance is defined as R
. A single-line model is used for better clarification of the
F
algorithm.
and Z
. Assume, that the fault occurs at a dis-
A
B
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. The fault resis-
L
329
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