Chauvin Arnoux C.A 6549 Bedienungsanleitung Seite 73

 PI:
The measurement is started by pressing START /
STOP and stops automatically when the PI ratio has
been calculated, i.e. after 10 minutes, the time for
measuring the second insulation resistance value
needed for the calculation (the sample times can be
modifi ed with the , ,
Remark: in this mode, the DAR ratio will also be
calculated automatically if the times
needed to calculate it are less than the
second time needed to calculate the PI
ratio.
Important remarks:
What is the DD (Dielectric Discharge index)?
In the case of multilayer insulation, if one of the layers is defective but the resistance of all the others
is high, neither the quantitative insulation measurement nor the calculation of the PI and DAR quality
ratios will reveal the problem.
This makes it judicious to perform a dielectric discharge test, from which the DD term can be
calculated. This test measures the dielectric absorption of heterogeneous or multilayer insulation and
disregards parallel-surface leakage currents.
It involves applying a test voltage for long enough to electrically "charge" the insulation to be measured
(typically, a voltage of 500 V is applied for 30 minutes).
At the end of the measurement, the instrument causes a rapid discharge, during which the capacitance
of the insulation is measured; 1 minute later, the residual current circulating in the insulation is measured.
The DD term is then calculated as follows:
DD = current measured after 1 minute (mA) / [test voltage (V) x measured capacitance (F)]
The insulation quality rating as a function of the value found is as follows:
Note: The dielectric discharge test is especially well suited to insulation measurements on rotating
machines, and, in general, to insulation measurements on heterogeneous or multilayer insulations
containing organic materials.
and keys).
Value of DD Quality of insulation
7 < DD
4 < DD < 7
2 < DD < 4
DD < 2
73
MODE
Total Run Time
Manual Stop
Manual Stop + DD
Duration Sample
(h:m)
Timed Run 02:30
Timed Run + DD
DAR (s/s)
PI (m/m)
Very poor
Poor
Borderline
Good
00:10:00
(m:s)
00:10
30/60
1.0/10