Determining water in transformer paper insulation: effect of measuring oil water activity at two different locations

It is necessary to monitor the water content of the paper insulation (WCP) within a power transformer because, if it becomes too large, the paper insulation may age prematurely or the transformer may fail on overload. It is nearly always unfeasible to extract a paper insulation sample from a transformer for a laboratory measurement of its water content because it involves removing part of the insulation.