i will do absorption Ratio (AR) test for transformers in my job,and i know how to calculate the absorption Ratio

AR=\$ \frac{R_{60}}{R_{30}}\$

\$ R_{60}\$=Insulation Resistance after 60 second test

\$ R_{30}\$=Insulation Resistance after 30 second test

and some website says

absorption Ratio ≈ 1 means insulation resistance is bad absorption Ratio > 1.25 or 1.3 means insulation resistance is good

first,i can understand insulation resistance will become worse over time,but why won't the insulation resistance be the same in just 30 seconds ?

And when the insulation resistance the same in that 30 second,it means insulation resistance is bad ? why? why does it mean insulation resistance when \$ R_{60}\$ and \$ R_{30}\$ are nearly the same?

  • \$\begingroup\$ Do you naturally believe all websites? \$\endgroup\$
    – Andy aka
    Commented Aug 5, 2021 at 14:00
  • \$\begingroup\$ @Andyaka because all checklist and all website say that too.so i don't have any reason to say that they are incorrect \$\endgroup\$ Commented Aug 5, 2021 at 23:44


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