Modeling of electric apparatus for voltage sag investigation in customer power distribution system

This paper describes the measurement-based model of electric apparatus after a voltage sag occurrence. The terminal voltage and load current of a personal computer (PC), an inverter fluorescent light and an incandescent light were measured to find out the dependences of load characteristics on the voltage sag. The magnitude of the load current after a voltage sag depends on the duration of the voltage sag and residual voltage. In order to make it possible to take account of these transient load characteristics in the power quality estimation, a modified exponential load model is proposed. The current waveform is obtained by using the database on time variation in the parameters of the exponential model. The model of harmonic components of the load current is also developed. The proposed model enables us to estimate the load current in the large customer power distribution system when the voltage sag occurs