Minimizing dielectric frequency response measurement time by using multiple frequency signals

摘要

Modern technology and developments in signal acquisition and analysis techniques have provided new tools for transformer diagnostics. Of particular interest are Dielectric Response Measurements, DFR (also known as Frequency Domain Spectroscopy, FDS), a tool for investigating insulation properties of specific materials and material combinations, e.g., oil-paper systems. DFR was first introduced about 20 years ago and has been thoroughly evaluated in a number of research projects and field tests with good results (see reference list). Moisture assessment and bushing diagnostics in transformers as well as cable diagnostics and insulation testing in rotating machinery are important applications where DFR in combination with insulation modeling provides accurate information for decisions on maintenance and/or replacement. One drawback of the DFR methodology is that it takes a longer time to measure compared to traditional single-frequency tan delta measurements. For the first generation systems introduced more than 15 years ago, the measurement time was often hours. With the latest technology, using AC signals containing multiple frequency content, the measurement time is significantly reduced and a typical measurement down to 1 mHz takes only about 20 minutes.