Why is water killing power transformer insulation?

Water is a threat to the insulation of oil (or ester) insulated power transformers. It leads to reduced breakdown strength of the oil and an accelerated aging of the cellulose insulation. Dielectric frequency response analysis is a suitable and accurate way to assess the water content of the insulation and it helps to determine the condition and remaining lifetime of the transformer. Prior drawbacks of this technology, such as long measurement times and complex assessment, can be eliminated using modern software. The polarization depolarization current PDC+ technique, an improved version of the PDC measurement, reduces the measurement time up to a factor of 20. With this technology, a range from 1 kHz to 10 µHz can be measured in less than two hours. Further automation of the whole measurement and assessment process makes the PDC+ technique easy and reliable for all users.