Unique aspects of distribution system harmonics due to high impedance ground faults

The effects of the many sources of harmonics which occur on distribution systems are discussed and contrasted with the single source of harmonics from a high-impedance ground fault. Field data are presented which show the complexity of modeling the ambient harmonics and the simplicity of the change in the phasor value of the third harmonic which occurs due to a high-impedance ground fault. This phasor change is shown to be unique and predictable and hence suitable for use in detecting these faults. It is shown that variations in ambient harmonics may be greater than the change due to a high-impedance ground fault and must be considered in the fault detection system. Calculations of fault current harmonics are simpler than those for the ambient harmonics. >