Power Transformer Oil Breakdown voltage

[speedtronic]

Break down voltage of a power transformer oil is usullay in a range of 60 to 85 KV (as I observed). But for a 11kv to 220kv or 132kv power transformer, shouldn't this oil breakdown as soon as transformer is energized? please explain

 

[welshmadness]

At a guess, different viscosity oils are used in different transformer ratings?

 

[xraytek]

Break down voltage of a power transformer oil is usullay in a range of 60 to 85 KV (as I observed)

What was the distance between your test probes?
I asume the test you carry out determines whether or not moisture has got into the oil as it is hydroscopic like brake fluid.

My guess is that the oil will be rated at different temperatures like brake fluid, and that the Kv withstand will depend on the amount of oil between 2 parts.
Regards