A Review of Harmonic Mitigation Techniques

This paper provides an explanation of the various harmonic mitigation techniques available to solve harmonic problems in three phase power systems. Included are the advantages and disadvantages of each method, their normal circuit connection as well as typical performance that can be expected when each method is properly employed. In addition to explaining the theory of operation, useful charts and diagrams are provided so that the reader can directly apply this information for the analysis of their own power system circumstances. Users of adjustable speed drives (ASD) and other three phase (rectified) non-linear loads have many choices available when it comes to harmonic mitigation. In the consideration of various alternatives, much depends on the user’s objectives as well as the severity of harmonics contributed by internal loads. The typical list of alternative three phase harmonic mitigation equipment includes: Line reactors, Isolation transformers, K-Factor transformers, Tuned harmonic filters (fixed capacity or automatic switched multiple banks), IGBT based fast switched harmonic filters, Low pass harmonic filters, 12 & 18 pulse rectifiers, Phase shifting transformers, and Active harmonic filters. This paper explains the operation of each type of mitigation alternative and provides the typical results that can be achieved when each type is properly applied. There is no single solution that is universally superior. After careful problem analysis and a clear understanding of end user objectives, quite often the best economical and technical solution is a hybrid solution; that is the combination of multiple technologies.