2 how to measure pi – KYORITSU 3128 User Manual

Page 53

KEW3128

6. Measurement

6. 4

PI Measurement (Polarization Index)

6.4.1 Polarization Index

PI : Polarization Index

This is a test to check a temporal increase of leakage currents flowing on
insulations. To determine a Polarization Index, first, measure insulation
resistance at 1 min intervals for 10 min. Then, divide the final value by

the initial reading and calculate a ratio. PI is dependent on the shape of
insulations and influenced by moisture absorption, therefore, a check of PI

is important to diagnosis the insulation of cables.

Polarization index =

TIME 2

Insulation resistance value 3 or 10 min

after starting measurement

TIME 1

Insulation resistance value 30 sec or 1 min

after starting measurement

4.0 or more

4.0 ～ 2.0

2.0 ～ 1.0

1.0 or less

Criteria

Best

Good

Warning

Bad

6.4.2 How to measure PI

1. Select the “PI（Polarization Index）” on the Mode Selection Screen.

Refer to Basic Operation (=>P.21) and operate the Screen.