Year

2003

Degree Name

Doctor of Philosophy (PhD)

Department

School of Electrical, Computer and Telecommunications Engineering - Faculty of Informatics

Abstract

With many distribution customer loads being sensitive to excessive harmonic voltage distortion, electricity distribution network service providers should now be looking towards preventative measures to ensure that voltage distortion levels remain within limits set by the appropriate standards. Measures will need to be taken at the planning stage to ensure distribution systems are able to meet harmonic limits recommended by standards as distortion due to loads increases. This thesis describes the development of harmonics planning and analysis tools that allow effective system modelling and comparison with standards, particularly in the planning phase where details of loads are usually not accessible. In this thesis development of statistical harmonic models of residential, commercial and industrial load types to simulate the global behaviour of distorting loads at distribution substations is presented. Both time and phase diversities are included in the representative load models. A method to estimate the 95(superscript th) percentile cumulative probability level of harmonic voltage distortion in an MV distribution system as required by the present Australian harmonic standard (AS/NZS 61000.3.6) is also developed. Results from a harmonic monitoring programme carried out on a typical MV distribution system are used to establish parameters for the load models and also to confirm the relative accuracy of the proposed distortion level prediction technique. A generalised method to extend the IEC 61000-3-6 approach of allocating allowable harmonic emissions to the case where customers are distributed along an MV distribution system feeder having significantly different fault levels is presented. The method involves the determination of an allocation constant using the agreed loading of all customers and the system harmonic impedances. This approach typically requires an extensive amount of data that may not always be available to distribution network service provider engineers. An extension to the method has thus been established to cater for the situation where only limited data is available. This is achieved by looking at several extreme cases that classify the most common MV distribution system feeder configurations and through the use of correction factors for the allocation constant. Several example systems have been studied to illustrate the harmonic management tools described above. These case studies include identification of the key indicators for harmonic performance of a distribution system.

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