Insulation condition is considered to be perfect, if DAR>1.6 (long-term process of
the absorption capacity charging by low currents took place), satisfactory - if
1.3
≤
DAR
≤
1.6,
danger - if DAR<1.3 (short-term process of the absorption capacity charging by high
currents took place) within the temperature limits from 10 ºС to 30 ºС. In the latter case, as
well as if Dielectric Absorption Ratio is 20% more than the factory data, insulation drying is
recommended. For indication of the Dielectric Absorption Ratio during or after measurement
press button
.
Polarization Index (Pl)
is used to evaluate the ageing degree of the insulation on
cable lines, transformers and electric motors. It considers the change of dielectric structure
and therefore the increase of charged particles ability to move under action of electric field.
PI index is automatically calculated by the results of insulation resistance measurement by
the following formula:
PI =R
600
/
R
60
(2),
where R
60,
R
600
–
value of insulation resistance after 60 s and 600 s from the
beginning of measurement, respectively. Polarization Index calculation is OFF on default, it
can be set to ON by the user during the measurement parameters setting (see item 2.3.5).
It is recommended to use the following factors K
POL
to evaluate the insulation quality:
PI <1 –
service life of insulation is exhausted, the process of insulation resistance
decrease begins (possibly, to unacceptable level);
1
≤
PI <2 –
service life of insulation is decreased, but further operation is possible;
2
≤
PI <4 –
service life of insulation is sufficient, no operation limitations;
PI
≥
4 –
service life of insulation is not decreased, no operation limitations.
Note. Decision on operation of insulator with
PI
<1 shall be taken based on the
additional investigations: more frequent checks of insulation condition, forecasting of a
moment of resistance decrease to unacceptable level.
For indication of the Polarization Index during or after measurement press button
.
Note. If measurement time is not enough to calculate the Dielectric Absorption Ratio
or Polarization Index, then put the dashes in the corresponding items.
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