BDV of transformer oil

[panthripu]

Hi
I want to know , if there is any thumb rule or formula to know what should be transformer oil BDV if we know the operating voltage. Like my transformer has 34.5kV.

 

[mivey]

New oil: 35 kV minimum
287.5 kV+: 30 kV minimum
<287.5 kV: 25 kV minimum