Electrical interferences in SFRA measurements

Power transformers are still among the most costly and critical components in an electrical power network. Thus, the importance of a reliable condition assessment of these assets increases due to the aging of transformer fleets. The Sweep Frequency Response Analysis (SFRA) has become an important standard test and provides comprehensive information about the mechanical and electrical integrity of the active part of power transformers. Electrical as well as geometrical changes in the magnetic core, the winding assembly and the clamping structure can be detected by a comparison of an actual measurement with a reference measurement. In contrast to traditional diagnostic methods, the SFRA is sensitive to external electrical interferences which may limit the comparability and can consequently lead to misinterpretation of the measurement results. For an optimum suppression of narrowband and broadband noise, software-based as well as hardware-based techniques can be utilized. This article discusses the theory of different noise sources and noise suppression techniques. Different case studies show the efficacy of measurements even in harsh conditions