Have you resampled to confirm this sample? I would expect to see some hydrogen, but the presence of any Acetylene is disturbing since it always indicates an electrical arc in oil.
I don't know the answer, but I'm glad to talk about it.
Of course you know normally we think acetylene comes only from arcing and is accompanied by hydrogen (the simple key gas profile). I don't ever remember seeing acetylene without hydrogen off-hand.
You may have seen Halstead's theoretical curve Fig 1 of IEEEC57.104-1991 which shows that decomposition of oil produces hydrogen starting at lowest temperatures of any of the gases and hydrogen level increases from 225C to 1800C (the limits of the graph). But I have never placed too much faith in that curve.
hydrogen gas will leave the oil for the gas space much easier. So if it has been a long time since the fault you may find some of the hydrogen has gone to the gas space. But also if some of gas from your sample is lost during transport/analysis prior to vacuum extraction, that gas would likely be mostly hydrogen, since hydrogen comes out first.
