Islanding detection using impedance measurements techniques based on wavelet injection

Unintentional islanding phenomenon occurs when the distributed generator keeps injecting power to the grid after the power flow from the utility to the grid is interrupted. This event can result in serious injuries for the workers that are attempting to solve the problem of power failure. Several techniques have been proposed to avoid such an occurrence. This paper uses the measurement of the harmonic impedance of the electric system to detect the islanding event. The islanding condition will be detected through the harmonic impedance values of positive sequence, negative sequence and zero sequence, measured at the Point of Common Coupling (PCC) between the distributed generator and the grid. The simulations results shown that the negative sequence impedance had better performance in identifying the islanding, especially at the frequencies near to the fundamental frequency of the system.