抄録
In recent years, the superannuated transformers have been increasing. This causes such problems as requiring the maintenance of diagnosing internal abnormalities of a transformer and carrying out condition assessment. One of the ways to assess the internal condition is a gas analysis of the insulating oil. In this analysis, low-temperature overheating, the pre-phenomenon of the abnormal heating in the transformer, can be detected. Finding and dealing with this abnormality at the early stages reduce the risk of transformer failure. However, evolved gas of this analysis shows different patterns depending on the existence or non-existence of oxygen.
