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Very low frequency

About: Very low frequency is a research topic. Over the lifetime, 1540 publications have been published within this topic receiving 24233 citations. The topic is also known as: VLF.


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Proceedings ArticleDOI
01 Nov 2017
TL;DR: In this paper, a comparative analysis of the dielectric dissipation factor (DDF) or tanδ measurement is presented for 11kV cross-linked polyethylene (XLPE) cable at power frequency (50 Hz) and at very low frequency (VLF) diagnostic testing has emerged as a promising tool for insulation assessment of power cables.
Abstract: Very low frequency (VLF) high voltage testing had been used as a simple withstand test (go/no-go). Recently, VLF diagnostic testing has emerged as a promising tool for insulation assessment of power cables. The term VLF implies testing insulation with an excitation voltage at frequency of 0.1 Hz or lower. In this paper, a comparative analysis of the dielectric dissipation factor (DDF) or tanδ measurement is presented for 11-kV cross-linked polyethylene (XLPE) cable at power frequency (50 Hz) and at VLF. Here, the DDF response is measured from frequency 50 Hz to 0.1 Hz for four short cable sections where each sample has a capacitance lower than 300 pF. The experimental results show that the DDF value at 0.1 Hz is much higher than that at 50 Hz. Furthermore, differential tangent delta (DTD) and correlation of DDF values are calculated to incorporate with experimental results.

9 citations

Journal ArticleDOI
B Bleaney1

9 citations

27 Nov 2009
TL;DR: This paper presents the novel concept of OLFAR, the orbiting low frequency antennas for radio astronomy in space, and proposes an autonomous distributed sensor system in space to explore this new low-frequency band forRadio astronomy.
Abstract: New interesting astronomical science drivers for very low frequency radio astronomy have emerged, ranging from studies of the astronomical dark ages, the epoch of reionization, exoplanets, to ultra-high energy cosmic rays. Huge efforts are currently made to establish low frequency Earthbound instruments, since today’s technology is able to support this. However, astronomical observations with Earth-bound radio telescopes at very low frequencies are hampered by the ionospheric plasma, which scatters impinging celestial radio waves. This effect is larger at lower frequencies. Below about 5 MHz at night or about 10 MHz during daytime, the ionosphere is even opaque for radio waves. That means that Earth-bound radio astronomy observations in those bands would be severely limited in sensitivity and spatial resolution, or would be entirely impossible. A radio telescope in space would not be hampered by the Earths ionosphere, but up to now such a telescope was technologically and financially not feasible. However, extrapolation of current technological advancements in signal processing and small satellite systems imply that distributed low frequency radio telescopes in space could be feasible. We propose an autonomous distributed sensor system in space to explore this new low-frequency band for radio astronomy. The array will have identical elements (satellites), and ideally no central processing system. An advantage of such a system is that it is highly scalable and, due to the distributed nature, virtually insensitive to failure or non-availability of a fraction of its components. In this paper we present this novel concept of OLFAR, the orbiting low frequency antennas for radio astronomy in space.

9 citations

Journal ArticleDOI
TL;DR: In this article, the radio direction of these sources can be resolved if they are steady over the time of observation, unique in frequency and if the system consists of two or more stationary antennas possessing low side-lobe levels, positioned on the perimeter of a circle parallel to but above the ground plane, with their major lobes directed opposite to the center of the circle.
Abstract: Radio telescope sites require regular surveys of terrestrial radio information, viz. spectrum, flux density and radio direction. Terrestrial wireless radio sources may interfere in the radio telescope signals. Such signals received through wide band antennas in the VHF/UHF bands are amplified, integrated and spectrum-frame averaged. The radio direction of these sources can be resolved if they are steady over the time of observation, unique in frequency and if the system consists of two or more stationary antennas possessing low side-lobe levels, positioned on the perimeter of a circle parallel to but above the ground plane, with their major lobes directed opposite to the center of the circle. The maximum side-lobe level determines the maximum extent to which the antennas may be separated in angle in relation to the center of the circle. To resolve the sources, the signal is processed and then they are related to the radiation patterns with some algorithm. The overall observation angle can be made complete...

9 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
202320
202232
202156
202048
201942
201852