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Example: Fault current monitoring in a TNS system
Hints
(1) If the current transformers for the fault current detection needs to be grounded on the secondary
side this has to be done via the COM connector.
(2) Note that all conductors have to pass through the opening of the
residual current transformer in the same direction.
(3) A possible fault current flows through the protective
earth conductor (PE). It can only be detected if the PE
conductor is not routed through the residual current
transformer. If this cannot be avoided, e.g. due to using
a multi-wire cable with all conductors, the PE conductor
must be returned through the transformer.
(4) The cable or individual conductors should be routed through the
transformer as centered as possible in order to minimize
measurement errors.
(5) Neither the current transformers nor the measurement leads should be mounted or installed close to
strong magnetic fields. Measurement lines should also not be laid in parallel to power lines.
(6) For measurement range 1A only: The rated output of the transformer must be chosen that it is
reached when the rated secondary current (1A) flows. Consider that the burden of the transformer is
not only made up by the burden of the measurement input, but also by the resistance of the
measurement lines and the self-consumption of the transformer (copper losses).
A rated output selected too low leads to saturation losses in the transformer. The secondary
rated current can no longer be reached as the transformer reaches its limits before.
A rated output selected too high or an exceeding instrument security factor (>FS5) may cause
damage to the measuring inputs in case of overload.
(7) For the connection of the transformer to the fault detection module use ...
Conductor cross sections of 1.0 up to 2.5mm
Pairwise twisted conductors in case of short cable lengths
Shielded cables (shield grounded on one side only) in disturbed environment or in case of long
cable lengths
P10 Rev A
Device handbook LINAX PQ3000-PQ5000
2
(16-14 AWG)
23/102
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