Analysis of resonance problems and harmonic filter design in power factor correction capacitor applications

Increased use of power electronic control equipment has made it necessary to pay greater attention to harmonic voltages and currents in power systems. In power systems containing harmonic-producing equipment, application of power factor-correcting capacitors may lead to a resonance condition between the inductive reactance of the source and the capacitive reactance of the capacitor bank. If the resonance frequency occurs at or near a harmonic current produced by the load, severe voltage distortion and harmonic current amplification will occur. Very often, the increase in harmonic current is large enough to cause nuisance fuse blowing, breaker tripping and overheating of equipment. The paper begins with a review of the nature of harmonic currents and voltages and common sources of harmonic-producing equipment. This will be followed by the presentation of results generated from the software developed by the authors combining the strengths of Mathcad and Excel spreadsheet. The output from the program are the parallel resonant frequencies and the resulting voltage distortion due to harmonic-producing loads. In addition, the program also determines the value of the series inductor in the harmonic filter bank that would shift the parallel resonant frequency to a value less than the lowest-order harmonic term of the load. Also computed are the bus voltage distortion and filter harmonic duty. Work is in progress to extend the scope of the software from traditional passive filters to active filters