<Li> Furan testing - once every 2 years, subject to the transformer being in operation for min 5 years . </Li> <Table> <Tr> <Td> </Td> <Td> This section does not cite any sources . Please help improve this section by adding citations to reliable sources . Unsourced material may be challenged and removed . (January 2015) (Learn how and when to remove this template message) </Td> </Tr> </Table> <Tr> <Td> </Td> <Td> This section does not cite any sources . Please help improve this section by adding citations to reliable sources . Unsourced material may be challenged and removed . (January 2015) (Learn how and when to remove this template message) </Td> </Tr> <P> Some transformer oil tests can be carried out in the field, using portable test apparatus . Other tests, such as dissolved gas, normally require a sample to be sent to a laboratory . Electronic on - line dissolved gas detectors can be connected to important or distressed transformers to continually monitor gas generation trends . </P>

What is the purpose of oil in transformer