16
9.1. Measurement of the Polarization Index (PI)
When pressing the
Ε
key during the tests, the Polarization Index (PI) value
will be exhibited on the display. It is only possible to apply this function after
a minimum of 10 minutes of measurement; in case the key is pressed
before this minimum limit, the display will show the message of value
exhibition of PI value, but will not show any value. The polarization index is
the quotient between the values of the insulation resistance measured both
in 10 minutes and 1 minute. This index is useful to detect the damage of the
insulation resistance by the excessive presence of dust, dirt and greases or
through the action of chemical and physical agents.
=
PI
R
R
10 minutes
1 minute
9.2. Measurement of the Dielectric Absorption Index
(DAI)
When pressing the
Ε
key during the tests, the Dielectric Absorption Index
(DAI) value will be exhibited on the display. It is only possible to apply this
function after a minimum of 1 minute of measurement; in case the key is
pressed before this minimum limit, the display will show the message of
value exhibition of DAI value, but will not show any value. The polarization
index is the quotient between the values of the insulation resistance
measured at the 60 and 30 second, and it is useful for preventive and
predictive maintenance of windings (present in transformers, motors,
generators, etc.)
=
DAI
R
R
60 seconds
30 seconds
