IEEE Transformers Committee working group C57.139 has developed a guide for the interpretation of LTC DGA data. Key concepts expressed in the guide are:
• Many LTC abnormalities can be detected by means of statistically derived limits for combustible gas concentrations and combustible gas concentration ratios.
• Derivation of generic fault detection limits for all LTCs is not possible because of the wide variation in LTC design, breathing configuration, and operating conditions. Limits must be derived for specific models of LTCs.