FunctionFunction
EDS44x_D00201_07_M_XXDE/06.2020
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3.2 Operating principle of the EDS system
When an insulation monitoring device detects the occurrence of an insulation fault, it
starts the insulation fault location.
In the event of a first insulation fault, an undefined residual current flows in IT systems,
which is primarily defined by the system leakage capacitances and the value of the insu-
lation fault. The basic idea of insulation fault location is therefore generating a defined lo-
cating current I
L
that flows through the insulation fault. The locating current is driven by
the system voltage and can be located in the faulty outgoing circuit using the measuring
current transformer.
The locating current is generated by the locating current injector. It is limited in ampli-
tude and time. The amplitude depends on the size of the existing insulation fault and the
system voltage. It is limited depending on the settings.
The locating current flows from the locating current injector via the live lines to the insu-
lation fault position taking the shortest way. From there, it flows through the insulation
fault and the PE back to the locating current injector. This locating current pulse is detect-
ed by the measuring current transformers on the insulation fault path and signalled by
the connected insulation fault locator.
Locating pulse pattern:
The length of the pulse and pause intervals depends on the system conditions (R
F
, C
e
).
x s
y s
x s
y s
For further information, refer to the data sheet "Technical aspects
main catalogue part 1" in the chapter "Technical aspects when using insulation fault lo-
cation systems".
Measured value depending on the system leakage capacitance
The influence of system leakage capacitances may cause false indication
of the locating current.
The locating current of the locating current injector is limited. Due to this
limitation, the resistance of the insulation fault may be lower than the val-
ue signalled by the indicated locating current.
Project planning
During project planning it must be observed that there are no system
parts where the locating current can cause harmful reactions even in un-
favourable cases.
Symmetrical insulation faults
Under certain conditions, symmetrical insulation faults located down-
stream of the measuring current transformer are not detected. Low-fre-
quency residual currents (e.g. caused by converters) may prevent
insulation faults from being detected if their frequency is identical or al-
most identical to the test pulse frequency of the locating current injector.
Influence by other components
The insulation fault location can be disturbed by components, loads or
EMC influences within an IT system. Thus, secure localisation may not be
possible under all circumstances or false tripping may occur.
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