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Transient response plays a key role in the evaluation of the performance of grounding systems and for the protection of electrical installations under lightning strikes. The frequency spectrum of the lightning impulse contains harmonics components up to the megahertz range. The measured transient response of grounding systems under test may be distorted by spurious high frequency interference in the...
High current lightning strikes into earthing systems can result in ionization in the soil surrounding the earthing electrode. Most of the published studies investigating this phenomenon have assumed uniform one-layer soil, but soil ionization propagation in a multilayered soil sample has not been extensively addressed. Practical soils may consist of several layers with different water contents, and...
In the present work, epoxy nano composite samples of different clay content are subjected to water droplet initiated discharge tests using controlled harmonic content high voltage supply. The effect of a clay additive up to 1% by weight is shown to increase droplet contact angle by 8% with a subsequent reduction beyond this content. Using a UHF technique to identify the corona inception voltage, it...
An evaluation of the impedance of ground electrodes under dc, ac or impulse conditions requires reliable and accurate measurement of the current and earth potential rise (EPR) at the point of injection. This is commonly achieved in wired systems by arranging current-injection and measurement circuits in quadrature, but such wide-area test arrangements are not always possible due to prohibitive environmental...
In this work, the results of an experimental study of the impulse characteristic of practical ground electrodes consisting of horizontal conductors of various lengths, a grounding grid and full-scale tower footings are reported. These electrodes are installed at an outdoor test site having nonuniform soil, with equipment facilities for generating low- and high-magnitude impulse currents. The tests...
In this paper, field experiments and computer simulations of a sectionalised 88 m length horizontal earth electrode under different energisations (dc, variable frequency ac and transients of different shapes) are reported. From measurements of the voltage and current at the injection point, and by incrementally increasing the length of the test electrode, the effective length of the horizontal earth...
The risk of breakdown in mineral insulating oil constitutes a critical part in the insulation of high voltage apparatus such as transformer. This paper presents an experimental investigation on transformer oil dynamic breakdown characteristics when subjected to AC voltage. Breakdown tests were carried out on mineral oil samples using a sphere-sphere electrode test cell for various gap lengths 1 mm,...
In this paper, we present an experimental study on the properties of mineral oils under AC breakdown conditions. Breakdown tests were carried out on mineral oil samples using a sphere-sphere electrode test cell for various gap lengths 1 mm, 2.5 mm and 5 mm and at different voltage speed ramps: 0.5 kV/s, 2 kV/s and 3.5 kV/s. The dynamic impedance of the mineral oil samples was determined from the instantaneous...
In this paper, the behaviour of a horizontal electrode under impulse conditions is investigated experimentally at the Cardiff University outdoor earthing test facility. The test electrode consists of 88.5 m long copper conductor buried to a depth of 30 cm, and is divided into sections with test pits located along the electrode to enable access for voltage and current measurements along its length...
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