Year

2008

Degree Name

Doctor of Philosophy

Department

School of Electrical, Computer and Telecommunications Engineering

Abstract

Harmonic distortion in power systems is increasing worldwide, due principally to increased penetration of power electronic equipment in both transmission and distribution networks. In Australia, the key regulatory bodies have included acceptable levels of harmonic distortion in the licence conditions for network operators. However, the standard AS/NZS 61000.3.6 limiting harmonic distortion requires modification in order to be applied to Australian transmission networks.

The aspects of harmonic management considered in this thesis combine two elements: harmonic allocation and compliance assessment. Allocation is the process of limiting harmonic distortion at buses throughout the network by restricting the harmonic injection to be permitted by individual connected customers. Compliance assessment, as the name suggests, is verification that those limits are not exceeded. Neither process is clearly defined by AS/NZS 61000.3.6, yet both are required to prevent unacceptable harmonic levels.

In principle, maximum acceptable harmonic distortion levels should be a trade–off between minimising the costs of compliance with requirements and minimising the costs imposed by harmonic distortion. To identify, in a comprehensive theoretical manner, maximum acceptable levels of harmonic distortion on a transmission network would require detailed study of all equipment to be connected to the network having the potential to be susceptible to harmonic problems. Such a study is beyond the scope of this thesis. However, AS/NZS 61000.3.6 proposes a compatibility level to act as a boundary between acceptable network distortion levels and levels which low–voltage equipment must be able to tolerate without maloperation. Planning levels are derived from compatibility levels and are intended as performance measures at individual buses. Compatibility and planning levels form the basis for the AS/NZS 61000.3.6 harmonic management philosophy. This thesis examines the setting of planning levels in transmission networks.

Methods of allocating harmonic injection rights between multiple customers on a transmission network are investigated and developed. The present methodology recommended by AS/NZS 61000.3.6 does not guarantee that the harmonic emission levels allocated to individual customer installations will ensure that planning level exceedances are avoided. A revised harmonic allocation method is proposed which overcomes this. Modifications to the harmonic allocation process based on practical considerations are also suggested.

Harmonic allocation is purposeless if installations cannot be checked for compliance with allocated emission levels. Many authors have examined questions similar to this, without specifically identifying compliance with allocation as the eventual aim. Desired properties of a satisfactory compliance test are identified and several superficially attractive solutions are dismissed as a result. The proposed solution requires the evaluation of the Norton–equivalent circuit of the installation from field measurements.

This thesis integrates the allocation and compliance assessment tasks into a framework for harmonic management in transmission networks. For both allocation and compliance assessment, new techniques are proposed.

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Unless otherwise indicated, the views expressed in this thesis are those of the author and do not necessarily represent the views of the University of Wollongong.