Technical aspects affecting the use of insulation fault location systems 8. Insulation fault location in practice The following currents flow through the measuring current trans-formers on EDS insulation fault evaluators:• The test current I
T generated by the insulation fault R
F-N .• Residual currents I
n flowing through the system leakagecapacitances C
E-V and C
E-N and/or generated by R
F-V and R
F-N .• Transient leakage currents generated by switching andcontrol activities in the system.• Low-frequency leakage currents generated by the use ofconverters. 8.1 Requirements for reliable insulation fault location The insulation fault evaluator is charged with locating the insulati-on fault downstream of the measuring current transformer R
F-N . For this purpose, the test current caused by the insulation fault has to be detected reliably. Requirements:• The test current I
T is ≥ 2 mA and ≤ 50 mA for the EDS460/490.• The test current I
T is ≥ 0.2 mA and ≤ 5 mA for theEDS461/491.• The upstream capacitances C
E-V must be at least as large as the downstream capacitances C
E-N .• The total system leakage capacitance must not exceed specific values.• The sum of the test current and residual current flowing through the measuring current transformer must not exceed the following values:• Maximum 10 A (EDS460/490 – main circuit application) • Maximum 1 A (EDS461/491 – control circuit application)• As well as the residual current, the system frequency of the monitored system also affects reliable detection of the test current. See the fault curve below in this context.
Annex 1.9.2 186 Main catalogue part 1 – 08.2007/Insulation monitoring