Chauvin Arnoux C.A 6545 Bedienungsanleitung Seite 43

Then the PI or DAR ratios are calculated:
PI* = R R
10 min /
DAR = R
1 min /
The quality of the insulation is a function of the results.
For multilayer insulation, if one of the layers is defective but if all the others show strong resistance,
the calculation of the PI and PAR ratios is not sufficient to show up this type of problem.
It is therefore necessary to supplement the PI and DAR indications by a dielectric discharge test
used to calculate the DD term.
This test measures the dielectric absorption of heterogeneous or multilayer insulation while ignoring
the parallel-surface leak currents.
It consists of applying a test voltage for a period sufficient to electrically «charge» the insulation to
be measured (a typical value is the application of a 500 V voltage for 30 minutes).
The test voltage is chosen in the same way as the insulation measurement and the duration, for a
test with a programmed duration, in the SET-UP menu. The device then causes a fast discharge
during which the insulation capacity is measured then measured 1 minute after the residual current
circulating in the insulation.
The term DD is then computed from the relation below:
DD =
The indication of the insulation quality as a function of the resulting value is as follows:
Note: The dielectric discharge test is particularly suited for the insulation measurement of rotating
machines and in general for the insulation measurement of heterogeneous or multilayer
insulation containing organic materials.
Utilisation of R-DAR-PI-DD function
During or after a measurement, the R-DAR-PI-DD key is used to scroll through the values:
- DAR (if measurement > 1 min)
- PI* (if measurement > 10 min)
- DD can only be calculated 1 mn after the end of the insulation measurement and circuit discharge,
and only if it was selected before beginning the measurement
- Capacity in µF (only after the stopping of the measurement and the discharging of the circuit)
- Residual leakage current circulating in the installation in µA or nA
- Insulation resistance in MΩ or GΩ or TΩ
Note: During the measurement, the DAR value is not available if value DD was preselected before
the measurement, value PI is not available if values DAR or DD were preselected before the
measurement.
* For the PI calculation, the10 and 1 minute times can be modified in the SET-UP menu, so to adapt
to any normative changes or specific applications.
(2 values to be noted during a 10-min. measurement)
1 min
R (2 values to be noted during a 1-min. measurement)
30 s
DAR PI Condition of insulation
< 1 Insufficient if not
< 1,25
< 2
< 1,6 < 4
> 1,6 > 4
current measured after 1 minute (mA)
test voltage (V) x capacity measured (F)
DD value Insulation quality
DD > 7
7 > DD > 4
4 > DD > 2
DD < 2 Good insulation
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dangerous
Good
Excellent
Very bad
Bad
Doubtful