Power Quality Investigation of Back-to-Back Harmonic Filters for a High-Voltage Anode Foil Manufacturing Facility

The problem, as described by this high-voltage anode foil manufacturing facility, has included loss of the harmonic filter banks during utility power disturbances. During such disturbances, one or more formation machine(s) trip and rectifier(s) fault, both of which are critical to the continuous operation of the process. One recent disturbance resulted in significant failure of components in both filter banks. A power quality investigation commenced to determine the cause of the filter bank failure. This paper describes the results of the analytical methods employed. Field harmonic measurements determined the presence of voltage and current distortion and established an appropriate model for harmonic analysis of various likely system conditions. Harmonic analysis explained the tuning of the existing filter banks and changes to tuning that have occurred since installation several years ago, as well as determined the harmonic loading on each stage of the filters. Transient simulations identified existing problems and areas of concern, particularly in regard to transient overvoltages that resulted when switching either of the filter banks. Recommendations included alternatives to avoid possible failures in the future, most significantly the redesign of one of the harmonic filters and the application of surge protection.