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Title: Impulse measurements in earthing systems
Author: Lathi, Deepak
ISNI:       0000 0004 2735 5266
Awarding Body: Cardiff University
Current Institution: Cardiff University
Date of Award: 2012
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The behaviour of earth electrodes at power frequency conditions is well known. Several studies are going on at present, to understand the behaviour of earthing systems at transient impulse and high frequency conditions. The study of impulse measurements in earthing systems was carried out during this project, to understand the soil electromagnetic behaviour towards high frequency and variable AC/DC/impulse current magnitudes. Several measurement techniques and instrumentation used for the measurement of the earthing systems were surveyed. The limitations and the advantages of each approach have been identified, and the range of application determined. Extensive experiments were performed on the practical earth electrodes at the Cardiff University test site at Llanrumney, and at the Dinorwig power station earthing facilities. These experiments have revealed that there is reduction of impedance of earth electrodes over the frequency range 20Hz to 120kHz. Moreover, a pronounced effect of DC current magnitude was observed on the earth resistance of the electrodes over the range of 1mA to 500mA. The numerical modelling of the test configurations did not show the reduction in earth impedance over the frequency range 20Hz to 120kHz. To understand the different trends shown by the experiments and simulation, and the effect of frequency and current magnitude, a geological literature survey was carried out. This survey revealed that when the soil water electrolyte solution is subjected to high frequency electrical currents, it exhibits conductivity dispersion phenomenon. Conductivity dispersion is a phenomenon where conductivity of the clay water electrolyte solution increases by about 30% over a frequency range 20Hz to 100kHz. The geological literature survey also revealed that the polarisation effect in the soil water electrolyte is responsible for the non-linear current effect. Moreover, during this project, a new technique of FFT from impulse, was proposed to measure the earth electrode impedance, over a frequency range which is an inherent component of the impulse signals. The FFT from impulse signals, showed a good agreement of the measured earth impedance of the earth electrodes, with the measured earth impedance using the variable frequency scan method. FFT from impulse technique has an advantage over the variable frequency scan method, from the point of view of the time required for the measurement and the simplicity of the test source, for the measurement of the earth electrode impedance. Such a technique, could have impact on the testing at high current magnitudes, where impulse generation is much easier. Finally, the future scope of work is presented to explore the measurement of earth electrode impedance above the frequency of 120kHz and current magnitudes above 5A.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: TA Engineering (General). Civil engineering (General)