System description
14
TGH1394en/05.2007
3.2 Function of the EDS system
When an insulation fault is detected by the insulation monitoring device
in the IT system, the insulation fault location process will be started.
On the occurrence of a first insulation fault, a fault current essentially
determined by the system leakage capacitances flows in the IT system.
The fundamental idea in fault location is therefore to close the fault cur-
rent loop for a short period via a defined resistance. As a result of this
principle, the system voltage itself drives a test current containing a sig-
nal that can be evaluated.
The test current signals are generated periodically by the IRDH575 re-
spectively the PGH... . The test current is limited in amplitude and time.
As this happens, the system conductors are connected alternately to
earth via a defined resistance. The test current generated in this manner
depends on the size of the present insulation fault and the system volt-
age. It is limited according to the setting of the IRDH575 respectively
the PGH... . For planning purposes, it should be noted that no system
components are present in which this test current can bring about a
damaging reaction, even in unfavourable cases.
The test current pulse flows from the test device via the live parts, taking
the shortest path to the location of the insulation fault. From there, it
flows via the insulation fault and the PE back to the IRDH575 respec-
tively PGH... . This test current pulse is then detected by the measuring
current transformers located in the insulation fault path, and is signalled
by the connected insulation fault evaluator.
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