Transformer Monitoring - Rule of Thumb

Ask any Electrical Engineer about transformer monitoring, what matters to them is the healthiness of insulation (normally paper or normally called "cellulose") and the winding itself.

Found a good summary explaining the relationship of "bad" gases and its origin.

Not only is hydrogen present in all transformer faults, it is also the gas appearing first when a problem is developing. This means that detection of hydrogen traces is the best way to find out that something is going on. Plus, unlike most other gases, the generation rate of hydrogen increases proportionally to fault severity. The more serious the problem, the more hydrogen is generated! This behavior, coupled with the fact that hydrogen very rarely varies with load, makes it truly representative of the transformer status, at all times.
Carbon monoxide on the other hand, will vary with load. However, significant increases of carbon monoxide may be indicative of excessive overheating of cellulose. CALISTO 2 independently measures carbon monoxide precisely and accurately thus allowing you to correlate this measurement with other key values like hot spot temperature.

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