Measurement considerations using SFRA for condition assessment of Power Transformers

Sweep frequency response analyzer (SFRA) measurements are now an established method for condition assessment of power transformers. Since most of evaluation procedures is based on comparison between; 1) earlier measurements on same transformer, 2) measurements on sister transformers, or 3) phase to phase comparison on same transformer, the measurement accuracy and repeatability is of utmost importance. This paper will describe the influence of variation in cable setup and different kind of instrument weakness. The theoretical description will be backed up by field experience and measurements. Examples of measurements before and after an incident are mixed with measurements with same and "almost" same measurement configuration. Typical sources of errors are discussed and finally a simple guide will be presented how to achieve high reproducibility in SFRA measurements .