POWER-LINE IMPEDANCE AND THE ORIGIN OF THE LOW-FREQUENCY OSCILLATORY TRANSIENTS

Oscillatory transients represent a large portion of power-line disturbances, and among these, lower frequency oscillations (from about 1 to more than 20 kHz) appear particularly harmful to sensitive electronic equipment. This paper addresses three main issues: a) the origin and characterization of low-frequency transients, b) the determination of the impedance of power systems by deliberate switching of capacitors, and c) suggestions for remedies against these transients. The origin of low-frequency oscillatory transients is here attributed to the connection of large capacitances across live wires of the distribution systems. Measurements based on the connection of capacitors of known capacitance across the line are demonstrated to be a natural, accurate, and reproducible means of probing the power-line impedance. This turns out to be constituted by resistance and inductance in the frequency range explored. A physically significant equivalent circuit can be derived, based on the consideration that the three-wire distribution system (phase, neutral, safety wire) consists of three mutually coupled loops. The measurement technique (V-terminal data) permits derivation of both common-mode and differential-mode components. Several conclusions are drawn on the basis of the results of the time-domain transient analysis that allow the derivation of essential quantities of the phenomenon (peak voltage, duration, spectral content) and the suggestion of corrective measures. © 1990 IEEE