Computer Models for Complex Plant & System Based on Terminal Measurements

A method for obtaining models of complex plant and systems for use in transient voltage studies is described. The method is based upon determining the terminal impedance/ frequency characteristics of the plant or system under study over a wide frequency range. These characteristics are obtained from measurements performed at sampled frequencies with a programmable impedance meter and microcomputer. A method for correcting results for measuring lead length errors is also described. The method is shown to be applied to obtain models of single and three-phase transformers. These are validated comparing measured and calculated input impedances. The impedance/frequency characteristics are used to calculate the transfer functions across any two terminals of the system. The response to any excitation is calculated first in the frequency domain as the product of the frequency spectra and the transfer functions, and second in the time domain by the inverse Fourier transformation. This method is applied to calculate the second-pole-to-close switching transient generated in a breaker/cable/motor system. Again, measured and calculated results show excellent agreement. Although some limitations of this method appear at frequencies of up to 10 KHz, it is generally applicable to all items of system plant and to systems.