Harmonic resonance at a medium sized industrial plant

Harmonic resonance is a concern at an industrial plant because approximately 50 percent of the normal electrical load consists of computer equipment, switch mode power supplies and AC induction motor adjustable speed controllers. Due to the nonlinear characteristics of these loads, significant harmonic voltages and currents are produced on the electrical distribution system. Measurements were made with an harmonic analyzer at several locations in the electrical distribution system to quantify harmonic currents and voltages. The system impedance diagram, prepared from the system one line diagram, was used to model the electrical system and calculate power system natural frequencies. Calculations indicated harmonic resonance occurs near the fifth and seventh harmonic frequency depending on the configuration of the electrical power system. The plant equivalent circuit was prepared for several harmonic frequencies to allow the amplification of currents and voltages due to the effects of harmonic resonance