Time-dependent power systems impedance-interpretation and measuring problems

Problems of interpretation and measurement of the time-local impedance of a single phase power system loaded with switched and nonlinear loads are discussed. Simulations and measurements are presented for an active method of system identification for which narrow current spikes serve as system testing signals. Two practical realizations of harmonic generating devices are discussed and compared. The fact that even a highly harmonics polluting user cannot disturb too much the system voltage waveforms, makes the time-local linear system model useful if switched or even nonlinear loads are installed in the system. The problem of linear model approximation of a real power system is considered.