Harmonic resonance in power systems - a documented case

Harmonic resonance occurs in a power system when the power system natural frequency corresponds to the frequency of a source of harmonic current. This paper studies a real case of power system harmonic resonance that resulted in failure of 20-kV capacitor bank fuses. The load current harmonics are measured and analyzed to investigate the individual harmonics of the current and then by using the system impedance frequency characteristic, the voltage harmonic distortion and the corresponding capacitor current are determined. Calculation of the power system natural frequencies are given for various configurations of system shunt capacitance and results of the power system harmonic current and voltage on the capacitor fuse blown is studied. The paper proposes a criterion for the proper size of capacitor to put in service according to system frequency characteristic and current harmonics.