A new method for the calculation of subtransmission and distribution system transients based on the FFT

A method is presented for the calculation of bus voltage transients in an electric power system. The method is specifically intended for application to distribution and subtransmission networks during the application of large industrial loads. In this sense, the calculation is a power quality assessment. In particular, the case of load currents that are electronically switched may be analyzed. The essence of the method is the Fourier transform of Ohm´s law. The fast Fourier transform is used for computational efficiency. An interesting method for obtaining the Fourier transform of the bus transfer impedance is developed from the theory of parallel n-port networks. Examples are used to illustrate the calculation of bus voltage transients harmonic content. Although the latter is not a transient, harmonic voltages may be calculated by the proposed method under certain circumstance. The main application illustrated is that a transient which has dynamics which occur in a time interval of similar order as the period of the power frequency (i.e. 1/60 s for 60 Hz system)