MI 3205 TeraOhm XA 5kV
Measurements
46
Itot
Bad
In
sula
tion
Figure 5.16: The current/time diagram of a good and bad insulation tested with
dielectric discharge method
The dielectric discharge test is very useful for testing a multi-layer insulation. This test
can identify excess discharge currents that occur when one layer of a multi-layer
insulation is damaged or contaminated. This condition will not be detected by both the
spot test and the polarization index test. Discharge current will be higher for known
voltage and capacitance if an internal layer is damaged. The time constant of this
individual layer will differ from other layers, causing a higher current than that of a sound
insulation.
Warnings:
Refer to Warnings chapter for safety precautions!
Do not touch the test object during the measurement or before it is fully
discharged! Risk of electric shock!
Notes:
Consider displayed warnings when starting the measurement!
A high-voltage warning symbol appears on the display during the measurement to
warn the operator of a potentially dangerous test voltage.
Value of capacitance is measured during the final discharge of the test object.
If enabled, the instrument measures Dielectric Discharge (DD) when the
capacitance is within the range of 20 nF to 50
F.
The time duration of Graph R(t) is equal to the value of Timer3.
The Timer value could be very long (up to 99 minutes), so the Special automatic
decimation algorithm is used to write the Graph R(t) to the LCD.
If additional averaging (AVG) of the result value is turned on PI and DAR will not
be calculated (---).
