The analysis and quantifiaction of uncertainty for least life-cost electrical low voltage distribution design

[摘要] ENGLISH ABSTRACT:The purpose of this dissertation is to provide methods for designing and managing lowvoltage residential feeders. These methods can be applied to the problem of planningresidential networks under uncertainty while ensuring least life-cycle costs. By analysingcollected load data from various communities in South Africa, a new probabilistic model forrepresenting the load uncertainty of residential consumers was derived.This model uses the beta probability distribution to describe individual consumer loads over aperiod of time. Methods for combining the loads in linear combinations were used to derive anew probabilistic voltage regulation calculation procedure. This new method is different frompreviously developed voltage calculation methods in that it can be used to estimate theprobable voltage performance of a feeder over a period of time. A simplification of themethod is proposed which allows it to be implemented in any commercial spreadsheetprogram.The new probabilistic load model was also applied to the problem of calculating resistivelosses in residential low voltage feeders. A new probabilistic method was formulated and thismethod can be used to estimate the probable range of resistive loss in a feeder for a period oftime. This method is simple enough to implement in a commercial spreadsheet program.Probabilistic information about network and load parameter uncertainty is seldom availableand these uncertainties are best modelled using fuzzy numbers. The probabilistic calculationmethods cannot represent these uncertainties and only after applying a fuzzy-probabilisticapproach can both types of uncertainties be used. This is a significant enhancement to thecurrent methods and ensures that the uncertainty about the calculated results is realisticallyrepresented.The specification of load parameters for the methods was significantly simplified following aregression analysis of collected load data from South African communities. By specifying thedistribution of the consumption of individual consumers in a community, the other loadparameters can be estimated using a set of fitted linear regression equations. This greatly reduces the burden of specifying the load parameters and makes it possible for the proposedcalculation methods to be applied to the design of new feeders in practice.The distribution of the consumption of individual consumers can be specified using theaverage and the standard deviation of the consumptions of individual consumers. Accurateestimates of these parameters can be obtained from sales information and can be used tomanage existing networks effectively. Using the sales information with the proposed methodsenables more cost-effective upgrades of existing feeders low voltage feeders. Theidentification of potential problems in existing low voltage networks is also possible if thelayout of the feeders in a community is known.The use of the proposed methods is illustrated in step-by-step fashion. Typical inputparameters are used and all the required calculations with intermediate results are presented.

[发布机构] Stellenbosch University