Total Dissolved Gas in Oil

If the transformer is a sealed tank, the total gas value should not change drastically. There will be some fluctuation with the temperature of the oil, and the temperature will vary based on the loading, ambient conditions (temperature, day/night, sun/overcast, etc.) and whether or not the forced cooling (fans/pumps) is running.

A vented tank will show more fluctuation, but it should still follow a well-defined pattern due to the solubility of gas in the oil. Higher oil temperatures should lead to lower total gas, and lower temperatures should correspond to higher total gas.

If the total gas is rising, you should do a full dissolved gas analysis and compare it to a previous test. A rise in combustible gases (acetylene, ethylene, ethane) indicates arcing in the oil, and damage to the transformer is likely.

Can you explain to me why the amount of gas in the oil decreased with increasing temperature in the transformer oil (Higher oil temperatures should lead to lower total gas)? and please give me a reference that explains this phenomenon.

Thanks

If a transformer is healthy, total gas should stay fairly constant (not increasing) unless there are causes to make it go up (heating, insulation breakdown, faults, etc.). Even if it were fluctuation due to changes in loading, temperature, or similar, the "inertia" of the oil mass would damp out any sudden changes.

Have you considered that your severe fluctuation could be a problem between the sensor and the monitoring unit? I presume these are low-level signals, maybe 0-1mA or millivolts, so some sort of damage to the wiring or connectors can cause strange readings. Wouldn't be the first time.