Relation between faults and generated gases in transformer liquids

The very good electric behaviour of insulating liquids beside their thermal and ageing stability, thermal transport and self healing capability are some of the reasons for their use in transformers. Faults in the insulation of transformers are very often accompanied by gases which can be dissolved or undissolved according to the condition of the liquid, the amount of generated gases, the size of the gas bubbles and the time the bubble needs to ascent. In this paper the gassing behaviour of different insulating liquids for transformers is introduced. Different failures are simulated inside a transformer model simultaneously. The generated dissolved and undissolved gases are detected and correlated to the failure. Beside mineral based transformer oil, a synthetic ester liquid is investigated which is a good substitute for PCB and mineral oil in transformers. The commercial names of the liquids used here are SHELL DIALA D as mineral based transformer oil and MIDEL 7131 as ester liquid. The gassing behaviour of the above mentioned liquids is compared for each failure and the results are discussed