Thermal aging of power distribution transformers operating under nonlinear and balanced load conditions

The flow of harmonic current encountered in nowadays electrical installations causes numerous undesirable issues to the power grid. The most detrimental consequence is the premature aging or even failure of the in-service power distribution transformers from industrial facilities (originally designed to cope with the linear loads). Accordingly, the paper quantitatively examines the major thermal operating parameters of these transformers and predicts their lifetime expectancy under a certain harmonic load spectrum. The developed computation principle is based on the international standard recommendations and only demands the load current harmonic content (measured with a power quality analyzer) and the transformer rated data. The study is also carried out on a 250 kVA oil-type three-phase power distribution transformer from a pumping station