Transformer diagnostic testing: standards to diagnose equipment with Sweep Frequency Response analysis

BY VOLNEY NARANJO, Megger

Sweep Frequency Response Analysis (SFRA) has become a powerful tool in advanced power transformer assessments and probably one of the main and first tools used to diagnose troubled transformers or as a regular maintenance test. In addition to being able to detect problems related to the mechanical or electrical integrity of the transformer, the results can be compared to the outcomes of traditional tests such as Transformer Turn Ratio (TTR), winding resistance or leakage reactance.

The SFRA test is valuable when a baseline measurement is compared to a diagnostic if both tests were performed under best practices to guarantee repeatability of the results; however, as per the inherent characteristics of the SFRA test, repeatability can be easily compromised.

Hence, for its technical value and the importance of obtaining reliable measurements, it becomes necessary to run SFRA tests with best practices. International standardization and research entities have been working on developing SFRA testing standards and guides, and so far, there are four major reference documents: two approved standards and two guides.