Impact of AC/DC electric field in thermally generated dissolved gases in transformer oil

Here we report the combined effect of electric field with thermal stress on dissolved gas analysis (DGA). Dissolved gases detected from accelerated aging experiments show that AC electric field combined with thermal stress leads to higher gas generation than DC electric field with thermal stress or by thermal stress alone. Research reveals that the differences are caused by the divergent migration properties of the charged components under AC and DC electric fields. A mathematical explanation correlates the DGA results by proposing a carrier recombination coefficient parameter. The study suggests that dissolved gas content does not reflect the insulation performance of transformers by simply employing DGA without considering the operating condition of the transformer. It is essential that a comprehensive evaluation criterion should accompany DGA in order to accurately determine the insulation status.