23
Press the CONFIG key.
CONFIG
CONFIG
Total Run Time
---
Manual Stop
Manual Stop + DD
Timed Run (m:s)
2:00
Timed Run + DD
DAR (s/s)
30/60
PI (m/m) 1.0/10
A capacitance in parallel to the insulation resistance extends the settling times of the measurements. This can affect or even inhibit
the measurement of DAR or PI (depending on the time set for recording the first resistance value). The table below indicates the
typical values of the capacitances in parallel with the insulation resistance, making it possible to measure the DAR and the PI
without changing their preset durations.
100 k
W
1 M
W
10 M
W
100 M
W
1 G
W
10 G
W
100 G
W
500 V
20 µF
20 µF
10 µF
5 µF
2 µF
1 µF
1 µF
1,000 V
5 µF
5 µF
5 µF
2 µF
2 µF
1 µF
1 µF
2,500 V
2 µF
2 µF
2 µF
1 µF
0,5 µF
0 µF
0 µF
5,000 V
1 µF
1 µF
1 µF
0,5 µF
0,5 µF
0 µF
0 µF
10,000 V
0,5 µF
0,5 µF
0,5 µF
0,2 µF
0,2 µF
0 µF
0 µF
15,000 V
0,5 µF
0,5 µF
0,5 µF
0,2 µF
0,2 µF
0 µF
0 µF
3.6. 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.
The dielectric discharge test is especially well suited to measuring the insulation of revolving machines and more generally to
measuring the insulation on heterogeneous or multi-layer insulating materials containing organic substances.
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 induces rapid discharging, during which the
capacitance of the insulation is measured, then, one minute later, it measures the residual current flowing in the insulation.
The DD term is then calculated as follows:
DD = current measured after 1 minute (mA)/[test voltage (V) x measured capacitance (F)]
3.6.1. MEASUrEMENt
