When should dissolved gas analysis for transformer oil be performed?

DGA is typically performed on a routine schedule based on transformer criticality, age, and loading. High value transmission transformers often use semiannual or quarterly sampling, while less critical units may be annual. DGA should also be done after major events such as through faults, overloading, relay operations, oil leaks, oil processing, or after commissioning to establish a baseline. If abnormal gases trend upward, sampling frequency increases until the condition stabilizes or corrective action is taken.