Can any one tell what method (other than Nitrogen freezing) can be used to detect oil leakages in underground oil filled transmission lines of 132 KV ?

Nitrogen Freezing is more of a process for isolating a leak [ http://www.alstern-technologies.com...ezing.html ] as part of the repair instead a tool for leak detection on an operational system.

Are you looking for a real time monitoring process which will identify the leak on an ongoing basis?

Niel Leon
engineering.com