# Why is insulation resistance is bad when absorption Ratio ≈ 1 and insulation resistance is good when absorption Ratio >1.25 or 1.3?

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?

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