Fault location and forewarning on transmission systems using travelling wave transients
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This thesis examines the main circuit modelling fundamentals and fault location techniques that may be applied to electricity transmission networks. Using a statistical comparison, it then investigates both impedance and travelling wave based fault location methods. This appears to be a novel comparison as no publications have been identified which draw conclusions on the accuracy of these fault location techniques. This work subsequently led TransGrid to install a new commercial travelling wave fault location system on the New South Wales 330kV transmission network. Following the commissioning of this system, there was an ongoing process to store data that was being observed by the travelling wave recorders. This data was later cross- referenced to determine the fault location, and the waveform interpreted to identify the source of the travelling wave transient. However, this analysis has revealed that the theoretical accuracy of this travelling wave system was not as good as previously expected from publication. The source of the degradation was tracked down and found to centre on the frequency response of the coupling transducers used by most conventional travelling wave recording hardware. These errors are not currently considered in publication but can result in several kilometres of uncertainty in a fault location calculation. Hence, it can be concluded that the use of conventional substation current transducers can introduce additional uncertainty into travelling wave fault location calculations. The source and nature of this uncertainty has subsequently led to the development of a novel unsynchronised fault location algorithm based on the continuous wavelet transform. This new technique also uses an assessment of waveform polarity to distinguish between signals generated by solid or incipient line faults. Several unusual events have also been observed which have led to a number of new developments in fault location and forewarning. These include specific requirements for impedance algorithms during unearthed inter-circuit faults on double circuit lines. Similarly, this thesis presents the development of a new method to forewarn of faults within oil impregnated current transformers. This has been based on the high frequency transients observed by the travelling wave system prior to the failure of a 330kV current transformer. This thesis also identifies significant potential for travelling wave techniques to forewarn of developing insulator faults on overhead circuits.
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