Combustible gas testing on large oil filled transformers

The subject of combustible gas in power transformers is not a new one. This paper is intended to provide a basis for tests and to explain briefly the various methods of testing and evaluation of results. In examining transformers that have failed in service, it is often found that the failure has progressed for some time with evidence of heating insulation and oil. It is evident that many faults are preceded by an incipient stage of gradual deterioration with gas evolution. The relation of the character of a fault to the composition of the gases produced was investigated about 40 years ago by M. Bucholz in connection with his development of the Buchholz relay.¹ The Buchholz relay collects a sample of gas (Figure 1) which can be analyzed in several ways which will be explained shortly. Then in 1959, McGraw-Edison announced that it was using a method of total combustible gas testing which does not require a separate gas analysis and is much simpler.²