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7.3Polarization index（PI）and Absorption ratio(DAR) Test
The Polarization Index (PI) and Absorption Ratio Test (DAR) can only be
performed on uncharged circuits. Before testing, check that the test leads
are good and confirm that the circuit under test is charged or not.
Turn the rotary switch to gear, then press VSEL to select the voltage
value to test.
Press the SET key to set the corresponding mode. The LCD shows “10:01m”
as the polarization index mode in the lower left corner of the LCD, “60:15S”
as the absorption mode 15 second mode, and “60:30S” as the absorption mode
30 second mode. Small numbers do not show anything for the insulation
resistance measurement mode.
One end of the ground wire (black) is connected to the instrument
connection EARTH and the other end is connected to the ground end of the
circuit under test. One end of the high-pressure rod test line (red) is
connected to the other end of the instrument LINE and the head is in contact
with the circuit under test, and the TFRT test key is pressed. The LCD displays
the measured value. After the measured value is fixed, the absorbance or
polarization index can be read.
After the test is completed, press “ ” to view the divisor of the
absorption ratio or polarization index value (such as the value of 60S in
“60:15S” mode).Press “ ” to view the dividend of the absorption ratio
or polarization index value (such as the value of 15S in “60:15S” mode).Press
" " or " " again to return.
7.4Polarization Index (PI) and Absorption Ratio (DAR) Applications：
In engineering, insulation resistance and absorption ratio (or
polarization index) can reflect the degree of moisture in the insulation of
generators, oil-immersed power transformers and other equipment. The value
of the absorption ratio (or polarization index) decreases after the
insulation is wet (see Figure 1), so it is an important indicator of whether
the insulation is affected by moisture.
It should be pointed out that sometimes the insulation has obvious defects
(for example, the insulation breaks down under high pressure), and the
absorption ratio or polarization index value is still good. The absorption
ratio or polarization index cannot be used to find other local insulation
defects other than moisture and dirt.
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