Power-mains transients from connection of resistive loads and a possible capacitive mitigation

The voltage transient disturbances produced in power mains by the connection of resistive loads are analyzed theoretically and experimentally. The effect of a series inductance is included in the circuit model. A fast unidirectional (exponential) waveshape that reduces the instantaneous phase-to-neutral voltage is demonstrated. Differential- and common-mode components are separated, and the basic quantitative formulas are given. The case of the switching of resistive loads when a capacitor is installed across the line on the mains side of the switch is analyzed. The presence of such a capacitor results in the appearance of double-exponential transients that are considerably smoothed with a maximum rate of change without the capacitor. Low capacitance values are shown to be adequate for giving substantial smoothing, and this technique appears to be suitable for mitigating the rate-of-change related effects of the resistive-load switching. The analytical derivations are based on a three-wire circuit representation of the power line described previously by the authors (1990). The reliability of that lumped-constant model for the analysis of the low-frequency disturbances is confirmed