High Impedance Fault detection in Low Voltage Distribution Systems Using Wavelet and Harmonic Fault Indices

High Impedance Faults (HIF) are those faults which occur in a power system which will not produce enough fault current to operate conventional protection system or fuses. This paper proposes a decentralized protection system which can detect high impedance fault in low voltage distribution systems. Transformer neutral current is decomposed using discrete wavelet transform to detect disturbances in neutral current. Multi resolution wavelet analysis is used to detect the disturbances created in neutral current by a fault. The area under the plot of absolute value of detailed coefficients is used to develop a fault index. Harmonic analysis of the neutral current is also done to ensure the accuracy of the new technique. These techniques are applied in a test system and the results are validated for different possible load and load switching conditions in an LV distribution system.