Reduction in tan Delta as well as insulation resistance

[Aakash12845382]

For a current transformer, what it means if both insulation resistance and tan Delta are being reduced over a period. e.g. tan Delta reduced by 40% while insulation resistance reduced by 10 times

 

[prc]

When the insulation deteriorates, IR usually decreases, with an increase in the tan delta. Please check the measurements and insulation temperature at the time of measurement. IR decreases when the temperature goes up (halving for every 10 C), But the tan delta increases with the temperature.

 

[Latango]

Is there any cracks anywhere that might let a bit of moisture in? Dissipation and IR both drop from water ingress, especially at that level of drop.