Power quality assessment via physically based modeling and statistical methods

Power quality at the consumer site is affected by (a) temporary disturbances that may originate anywhere in the system and (b) waveform distortion from nonlinear loads. The sources of disturbances are multiple and with varying parameters. For example in many places of the world, the most frequent disturbances originate from lightning activity near electric installations. Lightning may result in flashover causing voltage sags to some portion of the distribution system, voltage swell to other areas, as well as interruption of power. The number of customers affected depends on the design of the system and placement of interruption devices, while the level of voltage sags or swells may depend on the grounding system, size of neutral, etc. To properly capture these effects, the system model should explicitly represent these design details of the system. This paper presents a model that quantifies the impact of grounding system design on the power quality. It is also pointed out that many of the causes are statistically distributed both in time and in space. Statistical methods represent the best way for meaningful assessment of their effects on power quality. When these methods are combined with physically based models of the system, they provide an excellent tool for correlating design options to power quality performance. Examples of this approach are presented in this paper using Monte Carlo simulation techniques. The approach is suitable for cost-benefit analysis.