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Fault locator (FLOC)
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The main objective of line protection and monitoring terminals is fast, selective and re-
liable operation for faults on a protected line section. Besides this, information on dis-
tance to fault is very important for those involved in operation and maintenance.
Reliable information on the fault location greatly decreases the downtime of the pro-
tected lines and increases the total availability of a power system.
The distance to the fault, which is calculated with a high accuracy, is stored for the last
ten recorded disturbances. This information can be read on the HMI or transferred via
serial communication within the Station Monitoring System (SMS) or Station Control
System (SCS).
The distance to fault can be recalculated for the latest 10 disturbances by using the mea-
suring algorithm for different fault loops or for changed system parameters.
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The distance-to-fault locator (FLOC-) in the REx 5xx terminals is an essential comple-
ment to different line protection functions, since it measures and indicates the distance
to the fault with great accuracy. Thus, the fault can be quickly located for repairs.
The calculation algorithm considers the effect of load currents, double-end infeed and
additional fault resistance.
The function indicates the distance to the fault as a percentage of the line length, in ki-
lometers or miles as selected on the HMI.
The accuracy of measurement depends somewhat on the accuracy of the system param-
eters as entered into REx 5xx (for example source impedances at both ends of the pro-
tected line). If some parameters have actually changed in a significant manner relative
to the set values, new values can be entered locally or remotely and a recalculation of
the distance to the fault can be ordered. In this way, a more accurate location of the fault
can be achieved.
Any start of the disturbance reporting unit also starts the operation of the FLOC- func-
tion. The distance to the fault automatically appears on the local HMI, if the fault is also
detected by the phase selection elements within the terminal. The currents and voltages
before and during the fault are available via SCS/SMS. The terminal saves, in any other
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